使用SpringBootApplication作为springboot启动类代码一般如下：
@SpringBootApplication
public class SpringBootApplicationDemo {
public static void main(String[] args) {
SpringApplication.run(SpringBootApplicationDemo.class,args);
}
}
先看启动时的SpringBootApplication
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(
excludeFilters = {@Filter(
type = FilterType.CUSTOM,
classes = {TypeExcludeFilter.class}
), @Filter(
type = FilterType.CUSTOM,
classes = {AutoConfigurationExcludeFilter.class}
)}
)
public @interface SpringBootApplication {
@AliasFor(
annotation = EnableAutoConfiguration.class
)
Class[] exclude() default {};
@AliasFor(
annotation = EnableAutoConfiguration.class
)
String[] excludeName() default {};
@AliasFor(
annotation = ComponentScan.class,
attribute = "basePackages"
)
String[] scanBasePackages() default {};
@AliasFor(
annotation = ComponentScan.class,
attribute = "basePackageClasses"
)
Class[] scanBasePackageClasses() default {};
}
除去元注解，包含了三个注解：@SpringBootConfiguration，@EnableAutoConfiguration和@ComponentScan。
SpringBootConfiguration
/**
* Indicates that a class provides Spring Boot application
* {@link Configuration @Configuration}. Can be used as an alternative to the Spring's
* standard {@code @Configuration} annotation so that configuration can be found
* automatically (for example in tests).
*
* Application should only ever include one {@code @SpringBootConfiguration} and
* most idiomatic Spring Boot applications will inherit it from
* {@code @SpringBootApplication}.
*
* @author Phillip Webb
* @since 1.4.0
*/
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration
public @interface SpringBootConfiguration {
}
根据注释@Configuration注解用允许在spring中倒入注册额外bean
第二个
@EnableAutoConfiguration，字面理解就是可以自动配置bean
第三个ComponentScan
/**
* Configures component scanning directives for use with @{@link Configuration} classes.
* Provides support parallel with Spring XML's {@code } element.
*
* Either {@link #basePackageClasses} or {@link #basePackages} (or its alias
* {@link #value}) may be specified to define specific packages to scan. If specific
* packages are not defined, scanning will occur from the package of the
* class that declares this annotation.
*
*
Note that the {@code } element has an
* {@code annotation-config} attribute; however, this annotation does not. This is because
* in almost all cases when using {@code @ComponentScan}, default annotation config
* processing (e.g. processing {@code @Autowired} and friends) is assumed. Furthermore,
* when using {@link AnnotationConfigApplicationContext}, annotation config processors are
* always registered, meaning that any attempt to disable them at the
* {@code @ComponentScan} level would be ignored.
*
* See {@link Configuration @Configuration}'s Javadoc for usage examples.
*
* @author Chris Beams
* @author Juergen Hoeller
* @author Sam Brannen
* @since 3.1
* @see Configuration
*/
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Repeatable(ComponentScans.class)
public @interface ComponentScan {
根据注释
Either {@link #basePackageClasses} or {@link #basePackages} (or its alias
- {@link #value}) may be specified to define specific packages to scan. If specific
- packages are not defined, scanning will occur from the package of the
- class that declares this annotation.
如果没有指定basePackageClasses或basePackages 只会扫描使用该注解修饰的类所在的包和改类以下的子包,如果要扫描其他包需要用basePackages来指定：如这样使用注解:@SpringBootApplication(scanBasePackages = {"com.test.**"})
所以默认使用方法：SpringBootApplication注解作用的主程序类需要在根包，spring对类的默认仅涵盖主程序所在包及子包.
conditionalOn解释：
@ConditionalOnBean（仅仅在当前上下文中存在某个对象时，才会实例化一个Bean）
@ConditionalOnClass（某个class位于类路径上，才会实例化一个Bean）
@ConditionalOnExpression（当表达式为true的时候，才会实例化一个Bean）
@ConditionalOnMissingBean（仅仅在当前上下文中不存在某个对象时，才会实例化一个Bean）
@ConditionalOnMissingClass（某个class类路径上不存在的时候，才会实例化一个Bean）
@ConditionalOnNotWebApplication（不是web应用）
@ConditionalOnClass：该注解的参数对应的类必须存在，否则不解析该注解修饰的配置类；
@ConditionalOnMissingBean：该注解表示，如果存在它修饰的类的bean，则不需要再创建这个bean；可以给该注解传入参数例如@ConditionOnMissingBean(name = "example")，这个表示如果name为“example”的bean存在，这该注解修饰的代码块不执行。
如下，没有加载redisTemplate的话，不会执行启动bean
@Bean
@ConditionalOnClass(name = "org.springframework.data.redis.core.RedisTemplate")
public ServiceBean getServiceBean(){
ServiceBean serviceBean = new ServiceBean();
serviceBean.setId("1");
serviceBean.setName("test");
System.out.println("我家在了serviceBean");
return serviceBean;
}
外部参数配置：
启动时使用命令行传参：java -jar app.jar --name="test"
springBoot配置信息中特殊值：SPRING_APPLICATION_JSON='{"name":"test"}'
如果是web应用，可以读取ServletConfig init参数
如果是web应用，可以读取SerletContext init参数
JNDI属性来自java:comp/env
java系统属性（System.getProperties()）
配置文件application.properties,application.yml,application-{profile}.properties,application-(profile).yml
@PropertiySource注解导入的配置：@PropertySource(value={"person.properties})
程序入口通过SpringApplication.setDefaultProperties方法设定的参数配置
@Component
@PropertySource(value = "serviceBean.properties")
public class PropertiesBean {
@Value("${id}")
private String id;
@Value("${name}")
private String name;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
profile机制：隔离环境，使配置仅在某个特定环境中使用
配置文件存放配置：
1.当前项目运行的盘符/config目录下：file:./config/
2.当前项目运行的目录下:file:./
3.classpath目录下config:classpath/config
4.classpath目录下:classpath:
以上按优先级顺序排列