1.9. Annotation-based Container Configuration
上一节 1.8. Container Extension Points
目录
下一节 1.10. Classpath Scanning and Managed
文章目录
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- 1.9. Annotation-based Container Configuration
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- Are annotations better than XML for configuring Spring?
- 1.9.1. @Required
- 1.9.2. Using @Autowired
- 1.9.3. Fine-tuning Annotation-based Autowiring with @Primary
- 1.9.4. Fine-tuning Annotation-based Autowiring with Qualifiers
- 1.9.5. Using Generics as Autowiring Qualifiers
- 1.9.6. Using CustomAutowireConfigurer
- 1.9.7. Injection with @Resource
- 1.9.8. Using @Value
- 1.9.9. Using @PostConstruct and @PreDestroy
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1.9. Annotation-based Container Configuration
1.9. 基于注解的容器配置
Are annotations better than XML for configuring Spring?
配置Spring，注释比XML更好吗?
The introduction of annotation-based configuration raised the question of whether this approach is “better” than XML. The short answer is “it depends.” The long answer is that each approach has its pros and cons, and, usually, it is up to the developer to decide which strategy suits them better. Due to the way they are defined, annotations provide a lot of context in their declaration, leading to shorter and more concise configuration. However, XML excels at wiring up components without touching their source code or recompiling them. Some developers prefer having the wiring close to the source while others argue that annotated classes are no longer POJOs and, furthermore, that the configuration becomes decentralized and harder to control.
基于注释的配置的引入引出了这样一个问题:这种方法是否比XML“更好”。
简短的回答是“视情况而定”。长话短说，每种方法都有其优缺点，
通常由开发人员决定哪种策略更适合他们。
由于其定义方式，注释在其声明中提供了大量上下文，从而使配置更短、更简洁。
但是，XML擅长在不修改源代码或重新编译组件的情况下连接组件。
一些开发人员更喜欢连接到接近源代码的地方，而另一些人则认为带注释的类
不再是pojo，而且配置变得分散且更难控制。
No matter the choice, Spring can accommodate both styles and even mix them together. It is worth pointing out that through its JavaConfig option, Spring lets annotations be used in a non-invasive way, without touching the target components source code and that, in terms of tooling, all configuration styles are supported by the Spring Tools for Eclipse.
无论选择什么，Spring都可以提供这两种风格，甚至可以将它们混合在一起。
值得指出的是，通过它的JavaConfig选项，Spring允许以非侵入性的方式使用注释，
而不涉及目标组件的源代码，
而且，就工具而言，Eclipse的Spring工具支持所有配置样式。
An alternative to XML setup is provided by annotation-based configuration, which relies on the bytecode metadata for wiring up components instead of angle-bracket declarations. Instead of using XML to describe a bean wiring, the developer moves the configuration into the component class itself by using annotations on the relevant class, method, or field declaration. As mentioned in Example: The RequiredAnnotationBeanPostProcessor, using a BeanPostProcessor in conjunction with annotations is a common means of extending the Spring IoC container. For example, Spring 2.0 introduced the possibility of enforcing required properties with the @Required annotation. Spring 2.5 made it possible to follow that same general approach to drive Spring’s dependency injection. Essentially, the @Autowired annotation provides the same capabilities as described in Autowiring Collaborators but with more fine-grained control and wider applicability. Spring 2.5 also added support for JSR-250 annotations, such as @PostConstruct and @PreDestroy. Spring 3.0 added support for JSR-330 (Dependency Injection for Java) annotations contained in the javax.inject package such as @Inject and @Named. Details about those annotations can be found in the relevant section.
基于注释的配置提供了XML设置的另一种选择，它依赖字节码元数据来连接组件，
而不是使用尖括号声明。
开发人员没有使用XML来描述bean连接，而是通过在相关类、方法或字段声明上
使用注释，将配置转移到组件类本身。
如示例中所述:RequiredAnnotationBeanPostProcessor使用
BeanPostProcessor与注释结合是扩展Spring IoC容器的常见方法。
例如，Spring 2.0引入了使用@Required注释强制执行必需属性的可能性。
Spring 2.5使遵循相同的通用方法来驱动Spring的依赖项注入成为可能。
从本质上讲，@Autowired注解提供了与Autowiring协作器中描述的相同的功能，
但是拥有更细粒度的控制和更广泛的适用性。
Spring 2.5还增加了对JSR-250注释的支持，比如@PostConstruct和@PreDestroy。
Spring 3.0增加了包含的JSR-330 (Java依赖注入)注释的 javax.inject 包支持，
如@Inject和@Named。
有关这些注释的详细信息可以在相关部分找到。
Annotation injection is performed before XML injection. Thus, the XML configuration overrides the annotations for properties wired through both approaches.
注释注入在XML注入之前执行。
因此，XML配置覆盖了通过这两种方法连接的属性的注释。
As always, you can register them as individual bean definitions, but they can also be implicitly registered by including the following tag in an XML-based Spring configuration (notice the inclusion of the context namespace):
和往常一样，你可以将它们注册为单独的bean definitions，
但是也可以通过在基于xml的Spring配置中包含以下标签
(注意包含上下文名称空间)来隐式地注册它们:
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
https://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
https://www.springframework.org/schema/context/spring-context.xsd">
<context:annotation-config/>
beans>
(The implicitly registered post-processors include AutowiredAnnotationBeanPostProcessor, CommonAnnotationBeanPostProcessor, PersistenceAnnotationBeanPostProcessor, and the aforementioned RequiredAnnotationBeanPostProcessor.)
(隐式注册的post-processors包括AutowiredAnnotationBeanPostProcessor, CommonAnnotationBeanPostProcessor, PersistenceAnnotationBeanPostProcessor，
和前面提到的RequiredAnnotationBeanPostProcessor。)
context:annotation-config/ only looks for annotations on beans in the same application context in which it is defined. This means that, if you put context:annotation-config/ in a WebApplicationContext for a DispatcherServlet, it only checks for @Autowired beans in your controllers, and not your services. See The DispatcherServlet for more information.
1.9.1. @Required
The @Required annotation applies to bean property setter methods, as in the following example:
@Required注释适用于bean属性setter方法，如下面的例子所示:
public class SimpleMovieLister {
private MovieFinder movieFinder;
@Required
public void setMovieFinder(MovieFinder movieFinder) {
this.movieFinder = movieFinder;
}
// ...
}
This annotation indicates that the affected bean property must be populated at configuration time, through an explicit property value in a bean definition or through autowiring. The container throws an exception if the affected bean property has not been populated. This allows for eager and explicit failure, avoiding NullPointerException instances or the like later on. We still recommend that you put assertions into the bean class itself (for example, into an init method). Doing so enforces those required references and values even when you use the class outside of a container.
这个注释表示，必须在配置时通过bean定义中的显式属性值或自动装配来
填充受影响的bean属性。
如果未填充受影响的bean属性，容器将抛出异常。
这允许出现迫切的和显式的失败，避免了NullPointerException实例
或以后类似的情况。
我们仍然建议将assertions放到bean类本身中(例如，放到init方法中)。
这样做会强制执行那些必需的引用和值，即使您在容器之外使用该类。
（assertions怎么理解，怎样的形式put到bean里面？）
The @Required annotation is formally deprecated as of Spring Framework 5.1, in favor of using constructor injection for required settings (or a custom implementation of InitializingBean.afterPropertiesSet() along with bean property setter methods).
从Spring Framework 5.1开始，@Required注释正式被弃用，支持使用
构造方法注入来进行必需的设置
(或者使用InitializingBean.afterPropertiesSet()的自定义实现以及
bean属性setter方法)。
1.9.2. Using @Autowired
JSR 330’s @Inject annotation can be used in place of Spring’s @Autowired annotation in the examples included in this section. See here for more details.
在本节包含的示例中，JSR 330的@Inject注释可以用来替代Spring
的@Autowired注释。
更多细节请看这里。
You can apply the @Autowired annotation to constructors, as the following example shows:
你可以对构造方法应用@Autowired注解，如下面的例子所示:
public class MovieRecommender {
private final CustomerPreferenceDao customerPreferenceDao;
@Autowired
public MovieRecommender(CustomerPreferenceDao customerPreferenceDao) {
this.customerPreferenceDao = customerPreferenceDao;
}
// ...
}
As of Spring Framework 4.3, an @Autowired annotation on such a constructor is no longer necessary if the target bean defines only one constructor to begin with. However, if several constructors are available and there is no primary/default constructor, at least one of the constructors must be annotated with @Autowired in order to instruct the container which one to use. See the discussion on constructor resolution for details.
从Spring Framework 4.3开始，如果目标bean只定义了一个构造函数，
就不再需要在构造函数上使用@Autowired注解。
但是，如果有几个构造函数可用，并且没有主/默认构造函数，
那么至少有一个构造函数必须用@Autowired注解，以指示容器使用哪一个。
有关构造函数解析的详细信息，请参见讨论。
You can also apply the @Autowired annotation to traditional setter methods, as the following example shows:
你也可以对传统的setter方法应用@Autowired注解，如下例所示:
public class SimpleMovieLister {
private MovieFinder movieFinder;
@Autowired
public void setMovieFinder(MovieFinder movieFinder) {
this.movieFinder = movieFinder;
}
// ...
}
You can also apply the annotation to methods with arbitrary names and multiple arguments, as the following example shows:
你也可以将注释应用到具有任意名称和多个参数的方法上，如下面的例子所示:
public class MovieRecommender {
private MovieCatalog movieCatalog;
private CustomerPreferenceDao customerPreferenceDao;
@Autowired
public void prepare(MovieCatalog movieCatalog,
CustomerPreferenceDao customerPreferenceDao) {
this.movieCatalog = movieCatalog;
this.customerPreferenceDao = customerPreferenceDao;
}
// ...
}
You can apply @Autowired to fields as well and even mix it with constructors, as the following example shows:
你也可以在字段上应用@Autowired表格，甚至可以和构造器混合使用，
如下面的例子所示:
public class MovieRecommender {
private final CustomerPreferenceDao customerPreferenceDao;
@Autowired
private MovieCatalog movieCatalog;
@Autowired
public MovieRecommender(CustomerPreferenceDao customerPreferenceDao) {
this.customerPreferenceDao = customerPreferenceDao;
}
// ...
}
Make sure that your target components (for example, MovieCatalog or CustomerPreferenceDao) are consistently declared by the type that you use for your @Autowired-annotated injection points. Otherwise, injection may fail due to a “no type match found” error at runtime.
确保您的目标组件(例如，MovieCatalog或CustomerPreferenceDao)
由您为@Autowire注释的注入点使用的类型一致地声明。
否则，注入可能会由于运行时出现“没有找到类型匹配”错误而失败。
For XML-defined beans or component classes found via classpath scanning, the container usually knows the concrete type up front. However, for @Bean factory methods, you need to make sure that the declared return type is sufficiently expressive. For components that implement several interfaces or for components potentially referred to by their implementation type, consider declaring the most specific return type on your factory method (at least as specific as required by the injection points referring to your bean).
对于通过类路径扫描找到的xml定义的bean或组件类，
容器通常预先知道具体的类型。
但是，对于@Bean工厂方法，您需要确保声明的返回类型具有足够的表达能力。
对于实现多个接口的组件，或者对于可能由其实现类型引用的组件，
考虑在您的工厂方法上声明最特定的返回类型
(至少与引用bean的注入点所要求的那样特定)。
You can also instruct Spring to provide all beans of a particular type from the ApplicationContext by adding the @Autowired annotation to a field or method that expects an array of that type, as the following example shows:
您还可以通过向需要该类型数组的字段或方法添加@Autowired注解
来要求Spring从ApplicationContext中提供所有特定类型的bean，
如下面的例子所示:
public class MovieRecommender {
@Autowired
private MovieCatalog[] movieCatalogs;
// ...
}
The same applies for typed collections, as the following example shows:
这同样适用于类型化集合，如下面的示例所示:
public class MovieRecommender {
private Set movieCatalogs;
@Autowired
public void setMovieCatalogs(Set movieCatalogs) {
this.movieCatalogs = movieCatalogs;
}
// ...
}
Your target beans can implement the org.springframework.core.Ordered interface or use the @Order or standard @Priority annotation if you want items in the array or list to be sorted in a specific order. Otherwise, their order follows the registration order of the corresponding target bean definitions in the container.
如果希望数组或列表中的项按特定顺序排序，您的目标bean可以实现org.springframework.core.Ordered接口，
或使用@Order或标准@Priority注释。
否则，它们的顺序遵循容器中相应目标bean定义的注册顺序。
You can declare the @Order annotation at the target class level and on @Bean methods, potentially for individual bean definitions (in case of multiple definitions that use the same bean class). @Order values may influence priorities at injection points, but be aware that they do not influence singleton startup order, which is an orthogonal concern determined by dependency relationships and @DependsOn declarations.
您可以在目标类级别和@Bean方法上声明@Order注释，
可能是针对单个bean definitions(在使用相同bean类的多个定义的情况下)。
@Order值可能会影响注入点的优先级，但是要注意它们不会影响
singleton 启动顺序， singleton 启动顺序是由依赖关系和
@DependsOn声明正相关决定的。
Note that the standard javax.annotation.Priority annotation is not available at the @Bean level, since it cannot be declared on methods. Its semantics can be modeled through @Order values in combination with @Primary on a single bean for each type.
注意标准的javax.annotation.Priority 注释在@Bean级别不可用，
因为它不能在方法上声明。
它的语义可以通过在每种类型的单个bean上结合@Order值和
@Primary来建模。
Even typed Map instances can be autowired as long as the expected key type is String. The map values contain all beans of the expected type, and the keys contain the corresponding bean names, as the following example shows:
即使是类型化的Map实例也可以自动实现，只要期望的key 类型是String。
map的value包含所有期望类型的bean，key包含相应的bean名称，
如下面的示例所示:
public class MovieRecommender {
private Map movieCatalogs;
@Autowired
public void setMovieCatalogs(Map movieCatalogs) {
this.movieCatalogs = movieCatalogs;
}
// ...
}
By default, autowiring fails when no matching candidate beans are available for a given injection point. In the case of a declared array, collection, or map, at least one matching element is expected.
默认情况下，当给定注入点没有匹配的候选bean可用时，自动装配将失败。
对于声明的数组、集合或映射，至少需要一个匹配元素。
The default behavior is to treat annotated methods and fields as indicating required dependencies. You can change this behavior as demonstrated in the following example, enabling the framework to skip a non-satisfiable injection point through marking it as non-required (i.e., by setting the required attribute in @Autowired to false):
默认行为是将带注释的方法和字段视为指示所需的依赖项。
您可以像下面的示例中所演示的那样更改此行为，从而使框架可以通过将
不可满足的注入点标记为非必需的
(即，通过将@Autowired中的 required 属性设置为false):
public class SimpleMovieLister {
private MovieFinder movieFinder;
@Autowired(required = false)
public void setMovieFinder(MovieFinder movieFinder) {
this.movieFinder = movieFinder;
}
// ...
}
A non-required method will not be called at all if its dependency (or one of its dependencies, in case of multiple arguments) is not available. A non-required field will not get populated at all in such cases, leaving its default value in place.
如果一个非必需的方法的依赖项(或者它的一个依赖项，在有多个参数的情况下)
不可用，那么它将根本不会被调用。
在这种情况下，将不会填充非必需字段，保留其默认值。
Injected constructor and factory method arguments are a special case since the required attribute in @Autowired has a somewhat different meaning due to Spring’s constructor resolution algorithm that may potentially deal with multiple constructors. Constructor and factory method arguments are effectively required by default but with a few special rules in a single-constructor scenario, such as multi-element injection points (arrays, collections, maps) resolving to empty instances if no matching beans are available. This allows for a common implementation pattern where all dependencies can be declared in a unique multi-argument constructor — for example, declared as a single public constructor without an @Autowired annotation.
构造方法和工厂方法参数注入是一种特殊情况，因为由于Spring的构造方法
解析算法可能会处理多个构造方法，@Autowired中的required属性有不同的含义。
默认情况下，构造方法和工厂方法参数是有效的，但在单构造函数场景中
有一些特殊规则，比如如果没有匹配的bean可用，则多元素注入点
(数组、集合、映射)解析为空实例。
这允许一种常见的实现模式，在这种模式中，所有依赖项都可以在一个唯一的
多参数构造函数中声明
——例如，在没有@Autowired注解的情况下，声明为一个单一的公共构造方法。
（这一大段没太看明白，@Autowired中的required有什么特例情况）
Only one constructor of any given bean class may declare @Autowired with the required attribute set to true, indicating the constructor to autowire when used as a Spring bean. As a consequence, if the required attribute is left at its default value true, only a single constructor may be annotated with @Autowired. If multiple constructors declare the annotation, they will all have to declare required=false in order to be considered as candidates for autowiring (analogous to autowire=constructor in XML). The constructor with the greatest number of dependencies that can be satisfied by matching beans in the Spring container will be chosen. If none of the candidates can be satisfied, then a primary/default constructor (if present) will be used. Similarly, if a class declares multiple constructors but none of them is annotated with @Autowired, then a primary/default constructor (if present) will be used. If a class only declares a single constructor to begin with, it will always be used, even if not annotated. Note that an annotated constructor does not have to be public.
在任何给定bean类中，只有一个构造函数可以声明@Autowired，
并将required属性设置为true，以指示当作为Spring bean使用时要
自动装配的构造函数。
因此，如果required属性的默认值为true，那么只有一个构造函数可以
使用@Autowired注解。
如果有多个构造函数声明注释，那么它们都必须声明required=false，
才能被认为是自动装配的候选者(类似于XML中的autowire=constructor)。
通过在Spring容器中匹配bean可以满足的依赖关系最多的构造函数将被选择。
如果没有一个候选函数可以满足，那么将使用主/默认构造函数(如果存在)。
类似地，如果一个类声明了多个构造函数，但是没有一个是用@Autowired注解的，
那么一个primary/default 构造函数(如果有的话)将会被使用。
如果一个类只声明了一个构造函数，那么它将始终被使用，即使没有注释。
请注意，带注释的构造函数不必是公共的。
The required attribute of @Autowired is recommended over the deprecated @Required annotation on setter methods. Setting the required attribute to false indicates that the property is not required for autowiring purposes, and the property is ignored if it cannot be autowired. @Required, on the other hand, is stronger in that it enforces the property to be set by any means supported by the container, and if no value is defined, a corresponding exception is raised.
建议在setter方法上使用@Autowired required属性来替换已弃用的@Required注释。
将required属性设置为false表示该属性对于自动装配目的是不需要的，
并且如果该属性不能自动装配，则忽略它。
另一方面，@Required更强，因为它强制通过容器支持的任何方式设置属性，
如果没有定义值，则会引发相应的异常。
Alternatively, you can express the non-required nature of a particular dependency through Java 8’s java.util.Optional, as the following example shows:
或者，您可以通过Java 8的Java .util.Optional 表示特定依赖，如下例所示:
public class SimpleMovieLister {
@Autowired
public void setMovieFinder(Optional movieFinder) {
...
}
}
As of Spring Framework 5.0, you can also use a @Nullable annotation (of any kind in any package — for example, javax.annotation.Nullable from JSR-305) or just leverage Kotlin builtin null-safety support:
在Spring Framework 5.0中，还可以使用@Nullable注释(任何包中的任何类型
——例如javax.annotation.Nullable) 或者只是利用Kotlin内置的
null-safety 支持:
leverage
英 /ˈliːvərɪdʒ/ 美 /ˈlevərɪdʒ/
n. 手段，影响力；杠杆作用；杠杆效率
v. 利用；举债经营
public class SimpleMovieLister {
@Autowired
public void setMovieFinder(@Nullable MovieFinder movieFinder) {
...
}
}
You can also use @Autowired for interfaces that are well-known resolvable dependencies: BeanFactory, ApplicationContext, Environment, ResourceLoader, ApplicationEventPublisher, and MessageSource. These interfaces and their extended interfaces, such as ConfigurableApplicationContext or ResourcePatternResolver, are automatically resolved, with no special setup necessary. The following example autowires an ApplicationContext object:
你也可以使用@Autowired的接口是众所周知的可解析依赖:
BeanFactory, ApplicationContext, Environment, ResourceLoader,
ApplicationEventPublisher，和MessageSource。
这些接口及其扩展接口，如ConfigurableApplicationContext或
ResourcePatternResolver，会自动解析，不需要特殊设置。
下面的例子自动生成一个ApplicationContext对象:
public class MovieRecommender {
@Autowired
private ApplicationContext context;
public MovieRecommender() {
}
// ...
}
The @Autowired, @Inject, @Value, and @Resource annotations are handled by Spring BeanPostProcessor implementations. This means that you cannot apply these annotations within your own BeanPostProcessor or BeanFactoryPostProcessor types (if any). These types must be ‘wired up’ explicitly by using XML or a Spring @Bean method.
@Autowired， @Inject， @Value，和@Resource注解是由
Spring BeanPostProcessor实现处理的。
这意味着您不能在自己的BeanPostProcessor或
BeanFactoryPostProcessor类型(如果有的话)中应用这些注释。
这些类型必须通过使用XML或Spring @Bean方法显式地“连接起来”。
1.9.3. Fine-tuning Annotation-based Autowiring with @Primary
1.9.3. 使用@Primary调整基于注释的自动装配
Because autowiring by type may lead to multiple candidates, it is often necessary to have more control over the selection process. One way to accomplish this is with Spring’s @Primary annotation. @Primary indicates that a particular bean should be given preference when multiple beans are candidates to be autowired to a single-valued dependency. If exactly one primary bean exists among the candidates, it becomes the autowired value.
由于按类型自动装配可能会导致多个候选，因此通常有必要对选择过程
进行更多的控制。
实现这一点的一种方法是使用Spring的@Primary注释。
@Primary表示当多个bean是要自动传递到单值依赖项的候选bean时，
应该优先给予特定bean。
如果候选对象中恰好有一个主bean，它就成为自动生成的值。
Consider the following configuration that defines firstMovieCatalog as the primary MovieCatalog:
考虑以下配置，它将firstMovieCatalog定义为主要的MovieCatalog:
@Configuration
public class MovieConfiguration {
@Bean
@Primary
public MovieCatalog firstMovieCatalog() { ... }
@Bean
public MovieCatalog secondMovieCatalog() { ... }
// ...
}
With the preceding configuration, the following MovieRecommender is autowired with the firstMovieCatalog:
通过以上配置，下面的MovieRecommender是使用firstMovieCatalog自动生成的:
public class MovieRecommender {
@Autowired
private MovieCatalog movieCatalog;
// ...
}
The corresponding bean definitions follow:
对应的bean definitions如下:
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
https://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
https://www.springframework.org/schema/context/spring-context.xsd">
<context:annotation-config/>
<bean class="example.SimpleMovieCatalog" primary="true">
bean>
<bean class="example.SimpleMovieCatalog">
bean>
<bean id="movieRecommender" class="example.MovieRecommender"/>
beans>
1.9.4. Fine-tuning Annotation-based Autowiring with Qualifiers
1.9.4. 使用限定符调整基于注释的自动装配
@Primary is an effective way to use autowiring by type with several instances when one primary candidate can be determined. When you need more control over the selection process, you can use Spring’s @Qualifier annotation. You can associate qualifier values with specific arguments, narrowing the set of type matches so that a specific bean is chosen for each argument. In the simplest case, this can be a plain descriptive value, as shown in the following example:
当一个主要候选对象可以被确定时，@Primary是一种通过类型使用多个
实例的自动装配的有效方法。
当需要对选择过程进行更多控制时，可以使用Spring的@Qualifier注释。
您可以将 qualifier 与特定的参数相关联，从而缩小类型匹配的范围，
以便为每个参数选择特定的bean。
在最简单的情况下，这可以是一个简单的描述性值，如下面的例子所示:
public class MovieRecommender {
@Autowired
@Qualifier("main")
private MovieCatalog movieCatalog;
// ...
}
You can also specify the @Qualifier annotation on individual constructor arguments or method parameters, as shown in the following example:
您还可以在单独的构造函数参数或方法参数上指定@Qualifier注释，如下面的例子所示:
```Java
public class MovieRecommender {
private MovieCatalog movieCatalog;
private CustomerPreferenceDao customerPreferenceDao;
@Autowired
public void prepare(
@Qualifier("main") MovieCatalog movieCatalog,
CustomerPreferenceDao customerPreferenceDao
) {
this.movieCatalog = movieCatalog;
this.customerPreferenceDao = customerPreferenceDao;
}
// ...
}
The following example shows corresponding bean definitions.
下面的示例显示了相应的bean definitions。
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
https://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
https://www.springframework.org/schema/context/spring-context.xsd">
<context:annotation-config/>
<bean class="example.SimpleMovieCatalog">
<qualifier value="main"/> 1
bean>
<bean class="example.SimpleMovieCatalog">
<qualifier value="action"/> 2
bean>
<bean id="movieRecommender" class="example.MovieRecommender"/>
beans>
1 The bean with the main qualifier value is wired with the constructor argument that is qualified with the same value.
2 The bean with the action qualifier value is wired with the constructor argument that is qualified with the same value.
1. 具有qualifier=main 值的bean与具有相同限定符值的构造函数参数连接。
2. 具有qualifier=action 值的bean与具有相同限定符值的构造函数参数连接。
For a fallback match, the bean name is considered a default qualifier value. Thus, you can define the bean with an id of main instead of the nested qualifier element, leading to the same matching result. However, although you can use this convention to refer to specific beans by name, @Autowired is fundamentally about type-driven injection with optional semantic qualifiers. This means that qualifier values, even with the bean name fallback, always have narrowing semantics within the set of type matches. They do not semantically express a reference to a unique bean id. Good qualifier values are main or EMEA or persistent, expressing characteristics of a specific component that are independent from the bean id, which may be auto-generated in case of an anonymous bean definition such as the one in the preceding example.
对于回退匹配，bean名称被视为默认的限定符值。
因此，您可以使用id为main而不是嵌套的qualifier元素来定义bean，
从而得到相同的匹配结果。
然而，尽管您可以使用这种约定来按名称引用特定的bean，
但@Autowired基本上是关于类型驱动的注入，带有可选的语义限定符。
这意味着，即使使用bean名称回退，限定符值也总是在类型匹配集中具有收缩语义。
他们没有语义表达独特的bean的引用id。
良好的qualifier值是 main 或EMEA或 persistent,
表达某个特定组件的特点是独立于bean id,这可能是在前面的一个例子中
匿名的情况下自动生成的bean definition。
Qualifiers also apply to typed collections, as discussed earlier — for example, to Set. In this case, all matching beans, according to the declared qualifiers, are injected as a collection. This implies that qualifiers do not have to be unique. Rather, they constitute filtering criteria. For example, you can define multiple MovieCatalog beans with the same qualifier value “action”, all of which are injected into a Set annotated with @Qualifier(“action”).
Qualifiers 也适用于类型化的集合，如前面所讨论的—例如，Set 。
在这种情况下，根据声明的Qualifiers，所有匹配的bean都作为一个集合注入。
这意味着限定符不必是惟一的。相反，它们构成了过滤标准。
例如，您可以用相同的qualifier 值“action”定义多个MovieCatalog bean，
所有这些bean都被注入到一个注解为 @qualifier(“action”) 的
Set 。
Letting qualifier values select against target bean names, within the type-matching candidates, does not require a @Qualifier annotation at the injection point. If there is no other resolution indicator (such as a qualifier or a primary marker), for a non-unique dependency situation, Spring matches the injection point name (that is, the field name or parameter name) against the target bean names and choose the same-named candidate, if any.
让 qualifier 值在类型匹配候选中针对目标bean名称进行选择，
不需要在注入点使用@Qualifier注释。
如果没有其他解析指示器(例如 qualifier 或 primary)，对于非唯一依赖情况，
Spring将注入点名称(即字段名或参数名)与目标bean名称匹配，
并选择同名的候选对象(如果有的话)。
That said, if you intend to express annotation-driven injection by name, do not primarily use @Autowired, even if it is capable of selecting by bean name among type-matching candidates. Instead, use the JSR-250 @Resource annotation, which is semantically defined to identify a specific target component by its unique name, with the declared type being irrelevant for the matching process. @Autowired has rather different semantics: After selecting candidate beans by type, the specified String qualifier value is considered within those type-selected candidates only (for example, matching an account qualifier against beans marked with the same qualifier label).
也就是说，如果您打算通过名称表示注释驱动的注入，请不要主要使用@Autowired，
即使它能够通过bean名称在类型匹配的候选者中进行选择。
相反，使用JSR-250 @Resource注释，它在语义上定义为通过惟一名称标识
特定的目标组件，声明的类型与匹配过程无关。
@Autowired有相当不同的语义:在按类型选择候选bean之后，指定的字符串
qualifier 值只在那些类型选择的候选者中被考虑
(例如，将一个帐户 qualifier 与用相同 qualifier label 标记的bean相匹配)。
For beans that are themselves defined as a collection, Map, or array type, @Resource is a fine solution, referring to the specific collection or array bean by unique name. That said, as of 4.3, collection, you can match Map, and array types through Spring’s @Autowired type matching algorithm as well, as long as the element type information is preserved in @Bean return type signatures or collection inheritance hierarchies. In this case, you can use qualifier values to select among same-typed collections, as outlined in the previous paragraph.
对于本身定义为collection、Map或array类型的bean，
@Resource是一个很好的解决方案，它通过惟一的名称引用特定的集合或数组bean。
也就是说，在4.3，collection中，您也可以通过Spring的@Autowired类型
匹配算法来匹配Map和array类型，只要元素类型信息在@Bean返回类型签名
或集合继承层次结构中保留。
在这种情况下，您可以使用qualifier 值在相同类型的集合中进行选择，
如前一段所述。
As of 4.3, @Autowired also considers self references for injection (that is, references back to the bean that is currently injected). Note that self injection is a fallback. Regular dependencies on other components always have precedence. In that sense, self references do not participate in regular candidate selection and are therefore in particular never primary. On the contrary, they always end up as lowest precedence. In practice, you should use self references as a last resort only (for example, for calling other methods on the same instance through the bean’s transactional proxy). Consider factoring out the affected methods to a separate delegate bean in such a scenario. Alternatively, you can use @Resource, which may obtain a proxy back to the current bean by its unique name.
在4.3中，@Autowired也考虑注入的自我引用(也就是说，对当前注入的bean的引用)。
注意，self注入是一种退路。对其他组件的常规依赖始终具有优先级。
从这个意义上说，自我参照不参与候选人的定期选择，因此，尤其从来没有初选。
相反，它们总是优先级最低的。在实践中，您应该仅将self引用用作最后的手段
(例如，通过bean的事务代理调用同一实例上的其他方法)。
在这种情况下，考虑将受影响的方法分解为单独的委托bean。
或者，您可以使用@Resource，它可以通过当前bean的唯一名称获得回它的代理。
Trying to inject the results from @Bean methods on the same configuration class is effectively a self-reference scenario as well. Either lazily resolve such references in the method signature where it is actually needed (as opposed to an autowired field in the configuration class) or declare the affected @Bean methods as static, decoupling them from the containing configuration class instance and its lifecycle. Otherwise, such beans are only considered in the fallback phase, with matching beans on other configuration classes selected as primary candidates instead (if available).
尝试在同一个配置类上注入来自@Bean方法的结果实际上也是一个自引用场景。
要么在实际需要的方法签名中惰性地解析这些引用(与配置类中的自动生成字段相反)，
要么将受影响的@Bean方法声明为静态方法，将它们与包含的配置类实例及其生命
周期解耦。
否则，只在回退阶段考虑这样的bean，而选择其他配置类上的匹配bean作为主要
候选对象(如果可用)。
@Autowired applies to fields, constructors, and multi-argument methods, allowing for narrowing through qualifier annotations at the parameter level. In contrast, @Resource is supported only for fields and bean property setter methods with a single argument. As a consequence, you should stick with qualifiers if your injection target is a constructor or a multi-argument method.
@Autowired适用于 字段，构造方法，和多参数方法，允许通过 qualifier
注解在参数级别上缩小范围。
相比之下，@Resource只支持具有单个参数的字段和bean属性设置器方法。
因此，如果注入目标是构造方法或多参数方法，则应该坚持使用 qualifiers。
You can create your own custom qualifier annotations. To do so, define an annotation and provide the @Qualifier annotation within your definition, as the following example shows:
您可以创建自己的自定义 qualifier 注释。
为此，定义一个注释并在定义中提供@Qualifier注释，如下例所示:
@Target({ElementType.FIELD, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@Qualifier
public @interface Genre {
String value();
}
Then you can provide the custom qualifier on autowired fields and parameters, as the following example shows:
然后你可以在autowired字段和参数上提供自定义 qualifier，如下面的例子所示:
public class MovieRecommender {
@Autowired
@Genre("Action")
private MovieCatalog actionCatalog;
private MovieCatalog comedyCatalog;
@Autowired
public void setComedyCatalog(@Genre("Comedy") MovieCatalog comedyCatalog) {
this.comedyCatalog = comedyCatalog;
}
// ...
}
Next, you can provide the information for the candidate bean definitions. You can add tags as sub-elements of the tag and then specify the type and value to match your custom qualifier annotations. The type is matched against the fully-qualified class name of the annotation. Alternately, as a convenience if no risk of conflicting names exists, you can use the short class name. The following example demonstrates both approaches:
接下来，您可以为候选bean definition 提供信息。
你可以添加
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
https://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
https://www.springframework.org/schema/context/spring-context.xsd">
<context:annotation-config/>
<bean class="example.SimpleMovieCatalog">
<qualifier type="Genre" value="Action"/>
bean>
<bean class="example.SimpleMovieCatalog">
<qualifier type="example.Genre" value="Comedy"/>
bean>
<bean id="movieRecommender" class="example.MovieRecommender"/>
beans>
In Classpath Scanning and Managed Components, you can see an annotation-based alternative to providing the qualifier metadata in XML. Specifically, see Providing Qualifier Metadata with Annotations.
在类路径扫描和托管组件中，可以看到以XML提供限定符元数据的基于注释的替代方法。
具体地说，请参见章节 - Providing Qualifier Metadata with Annotations。
In some cases, using an annotation without a value may suffice. This can be useful when the annotation serves a more generic purpose and can be applied across several different types of dependencies. For example, you may provide an offline catalog that can be searched when no Internet connection is available. First, define the simple annotation, as the following example shows:
在某些情况下，使用没有值的注释就足够了。
当注释用于更通用的目的，并且可以跨几种不同类型的依赖项应用时，这一点很有用。
例如，您可以提供一个脱机目录，当没有可用的Internet连接时可以搜索该目录。
首先，定义简单注释，如下例所示:
@Target({ElementType.FIELD, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@Qualifier
public @interface Offline {
}
Then add the annotation to the field or property to be autowired, as shown in the following example:
然后将注释添加到要自动实现的字段或属性，如下面的例子所示:
public class MovieRecommender {
@Autowired
@Offline 1
private MovieCatalog offlineCatalog;
// ...
}
1 This line adds the @Offline annotation.
这一行增加了 @Offline 标签
Now the bean definition only needs a qualifier type, as shown in the following example:
现在，bean definition只需要一个 qualifier 类型，如下面的示例所示:
<bean class="example.SimpleMovieCatalog">
<qualifier type="Offline"/> 1
bean>
1 This element specifies the qualifier.
此元素指定 qualifier。
You can also define custom qualifier annotations that accept named attributes in addition to or instead of the simple value attribute. If multiple attribute values are then specified on a field or parameter to be autowired, a bean definition must match all such attribute values to be considered an autowire candidate. As an example, consider the following annotation definition:
您还可以定义自定义的 qualifier 注释，这些注释除了简单的value属性外，
还接受指定的属性。
如果在要自动装配的字段或参数上指定了多个属性值，
那么bean定义必须匹配所有这些属性值，才能被认为是自动装配的候选者。
作为一个例子，考虑下面的注释定义:
@Target({ElementType.FIELD, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@Qualifier
public @interface MovieQualifier {
String genre();
Format format();
}
In this case Format is an enum, defined as follows:
在本例中，格式是枚举，定义如下:
public enum Format {
VHS, DVD, BLURAY
}
The fields to be autowired are annotated with the custom qualifier and include values for both attributes: genre and format, as the following example shows:
要自动生成的字段用自定义 qualifier 进行注释，并包括两个属性的值:genre和format，
如下面的例子所示:
public class MovieRecommender {
@Autowired
@MovieQualifier(format=Format.VHS, genre="Action")
private MovieCatalog actionVhsCatalog;
@Autowired
@MovieQualifier(format=Format.VHS, genre="Comedy")
private MovieCatalog comedyVhsCatalog;
@Autowired
@MovieQualifier(format=Format.DVD, genre="Action")
private MovieCatalog actionDvdCatalog;
@Autowired
@MovieQualifier(format=Format.BLURAY, genre="Comedy")
private MovieCatalog comedyBluRayCatalog;
// ...
}
Finally, the bean definitions should contain matching qualifier values. This example also demonstrates that you can use bean meta attributes instead of the elements. If available, the element and its attributes take precedence, but the autowiring mechanism falls back on the values provided within the tags if no such qualifier is present, as in the last two bean definitions in the following example:
最后，bean definition 应该包含匹配的 qualifier 值。
这个示例还演示了您可以使用bean 的meta属性来代替
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
https://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
https://www.springframework.org/schema/context/spring-context.xsd">
<context:annotation-config/>
<bean class="example.SimpleMovieCatalog">
<qualifier type="MovieQualifier">
<attribute key="format" value="VHS"/>
<attribute key="genre" value="Action"/>
qualifier>
bean>
<bean class="example.SimpleMovieCatalog">
<qualifier type="MovieQualifier">
<attribute key="format" value="VHS"/>
<attribute key="genre" value="Comedy"/>
qualifier>
bean>
<bean class="example.SimpleMovieCatalog">
<meta key="format" value="DVD"/>
<meta key="genre" value="Action"/>
bean>
<bean class="example.SimpleMovieCatalog">
<meta key="format" value="BLURAY"/>
<meta key="genre" value="Comedy"/>
bean>
beans>
1.9.5. Using Generics as Autowiring Qualifiers
1.9.5. 使用泛型作为自动装配限定符
In addition to the @Qualifier annotation, you can use Java generic types as an implicit form of qualification. For example, suppose you have the following configuration:
除了@Qualifier注释之外，您还可以使用Java泛型类型作为一种隐式的限定形式。
例如，假设您有以下配置:
@Configuration
public class MyConfiguration {
@Bean
public StringStore stringStore() {
return new StringStore();
}
@Bean
public IntegerStore integerStore() {
return new IntegerStore();
}
}
Assuming that the preceding beans implement a generic interface, (that is, Store and Store), you can @Autowire the Store interface and the generic is used as a qualifier, as the following example shows:
假设前面的bean实现了一个通用接口（Store和 Store)，
你可以@Autowire Store接口，泛化的类被用作一个qualifier，如下面的例子所示:
@Autowired
private Store s1; // qualifier, injects the stringStore bean
@Autowired
private Store s2; //
qualifier, injects the integerStore bean
Generic qualifiers also apply when autowiring lists, Map instances and arrays. The following example autowires a generic List:
qualifier，注入integerStore bean泛型 qualifier 在自动装配列表、
映射实例和数组时也适用。
下面的例子自动生成一个通用列表:
// Inject all Store beans as long as they have an generic
// Store beans will not appear in this list
@Autowired
private List> s;
1.9.6. Using CustomAutowireConfigurer
1.9.6. 使用 CustomAutowireConfigurer
CustomAutowireConfigurer is a BeanFactoryPostProcessor that lets you register your own custom qualifier annotation types, even if they are not annotated with Spring’s @Qualifier annotation. The following example shows how to use CustomAutowireConfigurer:
customautowiresfigurer是一个BeanFactoryPostProcessor，
它允许您注册自己的自定义 qualifier 注释类型，即使它们没有
使用Spring的@Qualifier注释。
下面的例子展示了如何使用customautowiresfigurer:
<bean id="customAutowireConfigurer"
class="org.springframework.beans.factory.annotation.CustomAutowireConfigurer">
<property name="customQualifierTypes">
<set>
<value>example.CustomQualifiervalue>
set>
property>
bean>
The AutowireCandidateResolver determines autowire candidates by:
- The autowire-candidate value of each bean definition
- Any default-autowire-candidates patterns available on the element
- The presence of @Qualifier annotations and any custom annotations registered with the CustomAutowireConfigurer
AutowireCandidateResolver通过以下方式确定autowire候选者:
* 每个bean定义的自动候选值
* When multiple beans qualify as autowire candidates, the determination of a “primary” is as follows: If exactly one bean definition among the candidates has a primary attribute set to true, it is selected.
当多个bean符合自动装配候选时，确定“primary”的方法如下:
如果候选中恰好有一个bean定义的primary属性设置为true，则选择它。
1.9.7. Injection with @Resource
1.9.7. @Resource的注入标签
Spring also supports injection by using the JSR-250 @Resource annotation (javax.annotation.Resource) on fields or bean property setter methods. This is a common pattern in Java EE: for example, in JSF-managed beans and JAX-WS endpoints. Spring supports this pattern for Spring-managed objects as well.
Spring还通过在字段或bean属性setter方法上使用JSR-250 @Resource
注释来支持注入。
这是Java EE中的常见模式:例如，在 JSF 管理的bean和JAX-WS端点中。
Spring也为Spring管理的对象支持此模式。
@Resource takes a name attribute. By default, Spring interprets that value as the bean name to be injected. In other words, it follows by-name semantics, as demonstrated in the following example:
@Resource具有name属性。默认情况下，Spring将该值解释为要注入的bean名。
换句话说，它遵循了名称语义，如下面的示例所示:
public class SimpleMovieLister {
private MovieFinder movieFinder;
@Resource(name="myMovieFinder") 1
public void setMovieFinder(MovieFinder movieFinder) {
this.movieFinder = movieFinder;
}
}
1 This line injects a @Resource.
这一行通过@Resource注入
If no name is explicitly specified, the default name is derived from the field name or setter method. In case of a field, it takes the field name. In case of a setter method, it takes the bean property name. The following example is going to have the bean named movieFinder injected into its setter method:
如果没有显式指定名称，则默认名称派生自字段名称或setter方法。
对于字段，它采用字段名。
对于setter方法，它采用bean属性名。
下面的例子将把名为movieFinder的bean注入到它的setter方法中:
public class SimpleMovieLister {
private MovieFinder movieFinder;
@Resource
public void setMovieFinder(MovieFinder movieFinder) {
this.movieFinder = movieFinder;
}
}
The name provided with the annotation is resolved as a bean name by the ApplicationContext of which the CommonAnnotationBeanPostProcessor is aware. The names can be resolved through JNDI if you configure Spring’s SimpleJndiBeanFactory explicitly. However, we recommend that you rely on the default behavior and use Spring’s JNDI lookup capabilities to preserve the level of indirection.
随注释提供的名称由CommonAnnotationBeanPostProcessor感知的
ApplicationContext解析为一个bean名称。
如果显式配置Spring的SimpleJndiBeanFactory，则可以通过JNDI解析名称。
但是，我们建议您依赖于默认行为并使用Spring的JNDI查找功能来保持间接级别。
In the exclusive case of @Resource usage with no explicit name specified, and similar to @Autowired, @Resource finds a primary type match instead of a specific named bean and resolves well known resolvable dependencies: the BeanFactory, ApplicationContext, ResourceLoader, ApplicationEventPublisher, and MessageSource interfaces.
在使用@Resource没有指定显式名称的独占情况下，类似于@Autowired，
@Resource找到一个 primary 类型匹配而不是一个特定的命名bean，
并解析众所周知的可解析依赖项:BeanFactory, ApplicationContext,
ResourceLoader, ApplicationEventPublisher和MessageSource接口。
Thus, in the following example, the customerPreferenceDao field first looks for a bean named “customerPreferenceDao” and then falls back to a primary type match for the type CustomerPreferenceDao:
因此，在下例中，customerPreferenceDao字段首先查找名
为“customerPreferenceDao”的bean，然后返回到与类型
customerPreferenceDao匹配的primary类型:
public class MovieRecommender {
@Resource
private CustomerPreferenceDao customerPreferenceDao;
@Resource
private ApplicationContext context; 1
public MovieRecommender() {
}
// ...
}
1 The context field is injected based on the known resolvable dependency type:
ApplicationContext.
上下文字段是基于已知的可解析依赖类型注入的:ApplicationContext。
1.9.8. Using @Value
@Value is typically used to inject externalized properties:
@Value通常用于注入外部属性:
@Component
public class MovieRecommender {
private final String catalog;
public MovieRecommender(@Value("${catalog.name}") String catalog) {
this.catalog = catalog;
}
}
With the following configuration:
配置如下:
@Configuration
@PropertySource("classpath:application.properties")
public class AppConfig { }
And the following application.properties file:
和下面的 application.properties 文件:
catalog.name=MovieCatalog
In that case, the catalog parameter and field will be equal to the MovieCatalog value.
在这种情况下，目录参数和字段将等于MovieCatalog值。
A default lenient embedded value resolver is provided by Spring. It will try to resolve the property value and if it cannot be resolved, the property name (for example ${catalog.name}) will be injected as the value. If you want to maintain strict control over nonexistent values, you should declare a PropertySourcesPlaceholderConfigurer bean, as the following example shows:
Spring提供了缺省的宽松嵌入式值解析器。它将尝试解析属性值，
如果无法解析，属性名(例如${catalog.name})将作为值注入。
如果你想严格控制不存在的值，你应该声明一个
PropertySourcesPlaceholderConfigurer bean，如下面的例子所示:
@Configuration
public class AppConfig {
@Bean
public static PropertySourcesPlaceholderConfigurer propertyPlaceholderConfigurer() {
return new PropertySourcesPlaceholderConfigurer();
}
}
When configuring a PropertySourcesPlaceholderConfigurer using JavaConfig, the @Bean method must be static.
当使用JavaConfig配置PropertySourcesPlaceholderConfigurer时，
@Bean方法必须是静态的。
Using the above configuration ensures Spring initialization failure if any ${} placeholder could not be resolved. It is also possible to use methods like setPlaceholderPrefix, setPlaceholderSuffix, or setValueSeparator to customize placeholders.
如果任何一个${}占位符无法正确处理，使用上述配置将确保Spring在初始化过程中失败。
也可以使用setPlaceholderPrefix、setPlaceholderSuffix或setValueSeparator等
方法来定制占位符。
Spring Boot configures by default a PropertySourcesPlaceholderConfigurer bean that will get properties from application.properties and application.yml files.
Spring引导默认配置一个PropertySourcesPlaceholderConfigurer bean，
该bean将从application.properties 和 application.yml 文件获取属性。
Built-in converter support provided by Spring allows simple type conversion (to Integer or int for example) to be automatically handled. Multiple comma-separated values can be automatically converted to String array without extra effort.
Spring提供的内置转换器支持允许自动处理简单类型转换(例如到Integer或int)。
多个逗号分隔的值可以自动转换为字符串数组，而不需要额外的努力。
It is possible to provide a default value as following:
可以提供如下默认值:
@Component
public class MovieRecommender {
private final String catalog;
public MovieRecommender(@Value("${catalog.name:defaultCatalog}") String catalog) {
this.catalog = catalog;
}
}
A Spring BeanPostProcessor uses a ConversionService behind the scene to handle the process for converting the String value in @Value to the target type. If you want to provide conversion support for your own custom type, you can provide your own ConversionService bean instance as the following example shows:
Spring BeanPostProcessor在后台使用ConversionService来处理将
@Value中的字符串值转换为目标类型的过程。
如果你想为自己的自定义类型提供转换支持，你可以提供自己的
ConversionService bean实例，如下面的例子所示:
@Configuration
public class AppConfig {
@Bean
public ConversionService conversionService() {
DefaultFormattingConversionService conversionService = new DefaultFormattingConversionService();
conversionService.addConverter(new MyCustomConverter());
return conversionService;
}
}
When @Value contains a SpEL expression the value will be dynamically computed at runtime as the following example shows:
当@Value包含SpEL表达式时，该值将在运行时动态计算，如下例所示:
@Component
public class MovieRecommender {
private final String catalog;
public MovieRecommender(@Value("#{systemProperties['user.catalog'] + 'Catalog' }") String catalog) {
this.catalog = catalog;
}
}
SpEL also enables the use of more complex data structures:
SpEL还允许使用更复杂的数据结构:
@Component
public class MovieRecommender {
private final Map countOfMoviesPerCatalog;
public MovieRecommender(
@Value("#{{'Thriller': 100, 'Comedy': 300}}") Map countOfMoviesPerCatalog) {
this.countOfMoviesPerCatalog = countOfMoviesPerCatalog;
}
}
1.9.9. Using @PostConstruct and @PreDestroy
1.9.9. 使用@PostConstruct and @PreDestroy
The CommonAnnotationBeanPostProcessor not only recognizes the @Resource annotation but also the JSR-250 lifecycle annotations: javax.annotation.PostConstruct and javax.annotation.PreDestroy. Introduced in Spring 2.5, the support for these annotations offers an alternative to the lifecycle callback mechanism described in initialization callbacks and destruction callbacks. Provided that the CommonAnnotationBeanPostProcessor is registered within the Spring ApplicationContext, a method carrying one of these annotations is invoked at the same point in the lifecycle as the corresponding Spring lifecycle interface method or explicitly declared callback method. In the following example, the cache is pre-populated upon initialization and cleared upon destruction:
CommonAnnotationBeanPostProcessor不仅识别@Resource注释，
还识别JSR-250生命周期注释:javax.annotation.PostConstruct和
javax.annotation.PreDestroy。
在spring2.5中引入的对这些注释的支持为初始化回调和销毁回调中
描述的生命周期回调机制提供了另一种选择。
如果在Spring ApplicationContext中注册了
CommonAnnotationBeanPostProcessor，那么在生命周期中与对应的
Spring生命周期接口方法或显式声明的回调方法在同一点调用携带这些注释之一的方法。
在下面的例子中，缓存在初始化时被预填充，在销毁时被清除:
public class CachingMovieLister {
@PostConstruct
public void populateMovieCache() {
// populates the movie cache upon initialization...
}
@PreDestroy
public void clearMovieCache() {
// clears the movie cache upon destruction...
}
}
For details about the effects of combining various lifecycle mechanisms, see Combining Lifecycle Mechanisms.
有关组合各种生命周期机制的效果的详细信息，请参见组合生命周期机制。
Like @Resource, the @PostConstruct and @PreDestroy annotation types were a part of the standard Java libraries from JDK 6 to 8. However, the entire javax.annotation package got separated from the core Java modules in JDK 9 and eventually removed in JDK 11. If needed, the javax.annotation-api artifact needs to be obtained via Maven Central now, simply to be added to the application’s classpath like any other library.
与@Resource一样，@PostConstruct和@PreDestroy注释类型也是
JDK 6到8中标准Java库的一部分。
但是，整个javax.annotation包在JDK 9中的注释包与核心Java模块分离，
最终在JDK 11中被删除。
如果需要，可以使用 javax.annotation-api 构件 现在需要通过
Maven Central获得，只需像其他库一样将其添加到应用程序的类路径。