一、本文目录
- spring的简单使用方法
- spring初级容器XmlBeanFactory简单介绍
- spring初级容器XmlBeanFactory初始化
二、spring的简单使用
- 我们首先新建一个Student类，作为我们的示例bean
- spring的初衷，就是装载一个一个的bean，这些bean，其实就是简单的Java对象
public class Student {
private String name="JHXY";
private int age;
// 省略getter、setter、toString方法
- spring对应的applicationContext.xml文件中配置student实例bean
- 测试代码
public static void main(String[] args) {
XmlBeanFactory xmlBeanFactory =
new XmlBeanFactory(new ClassPathResource("applicationContext.xml"));
// 从XmlBeanFactory即：spring容器中，获取student bean
Student student = (Student) xmlBeanFactory.getBean("student");
System.out.println(student.getName());
}
-
测试结果
image.png XmlBeanFactory基本工作原理
- spring最基本的容器:XmlBeanFactory,我们熟知的ApplicationContent相当于spring的高级容器
- ApplicationContenxt高级容器在XmlBeanFactory基础上，添加了很多扩展功能和特性
- ClassPathResource封装了applicationContext.xml文件,作为XmlBeanFactory构造方法参数，创建XmlBeanFactory
三、spring初级容器XmlBeanFactory简单介绍
- 通过下载Spring源码,使用Intellij进行代码调试,我们已经将spring的源码下载到了本地，通过Intellij进行源码阅读，通过上面的简单使用，我们知道,spring的初级容器XmlBeanFactory在初始化的时候，其实就是通过简单的new XmlBeanFactory(new ClassPathResource("applicationContext.xml"));创建spring的初级容器
- 首先，我们来看下构造函数的参数，ClassPathResource对应的Resource是什么
-
我们先来看下ClassPathResource对应的类继承关系
Resource类继承图 - 我们可以看到
- ClassPathResource实现了Resource接口
- Resource接口继承了InputStreamSource
- 和ClassPathResource相似的还有InputStreamResource,ByteArrayResource,FileSystemResource
- 其实spring将所有的资源都抽象成一个InputStreamSource,这样，不同的来源使用不同的实现类。
-
Resource 接口中的方法
Resource接口中的方法
- exists():对资源状态的判断，资源是否存在
- isReadable():对资源状态的判断，是否是可读状态
- isOpen():对资源状态的判断，资源是否打开状态
- isFile():对资源状态的判断，判断是否是文件类型
- 通过类继承图可以知道，Resource接口继承了InputStreamSource，这就意味着所有的资源只要封装了Resource接口，就可以通过调用InputStreamSource的getInputStream方法来获取资源对应的InputStream输入流了
- 而资源是多种多样的，我们平时项目中的applicationContext.xml其实就是项目的classpath下的xml,ClassPathResource就是用来加载classpath路径下的资源文件
- 所以，各种Resource是如何加载资源的,我们通过示例中的ClassPathResource的getInputStream方法可以看出，ClasspathResource就是通过class或者classLoader的底层方法来加载的
/**
* This implementation opens an InputStream for the given class path resource.
* @see java.lang.ClassLoader#getResourceAsStream(String)
* @see java.lang.Class#getResourceAsStream(String)
*/
@Override
public InputStream getInputStream() throws IOException {
InputStream is;
if (this.clazz != null) {
is = this.clazz.getResourceAsStream(this.path);
}
else if (this.classLoader != null) {
is = this.classLoader.getResourceAsStream(this.path);
}
else {
is = ClassLoader.getSystemResourceAsStream(this.path);
}
if (is == null) {
throw new FileNotFoundException(getDescription() + " cannot be opened because it does not exist");
}
return is;
}
- 综上，我们可以得出结论：Resource就是spring内部资源的一个抽象，而InputStreamResource的接口实现，使我们对各种来源的资源都可以轻松的获取对应的输入流InputStream
四、spring初级容器XmlBeanFactory的初始化
- 我们知道，创建spring初级容器XmlBeanFactory，通过XmlBeanFactory构造函数直接创建，先来看下XmlBeanFactory的构造函数
public class XmlBeanFactory extends DefaultListableBeanFactory {
//XmlBeanDefinitionReader用于读取资源的reader组件
private final XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(this);
/**
* Create a new XmlBeanFactory with the given resource,
* which must be parsable using DOM.
* @param resource the XML resource to load bean definitions from
* @throws BeansException in case of loading or parsing errors
*/
public XmlBeanFactory(Resource resource) throws BeansException {
this(resource, null);
}
/**
* Create a new XmlBeanFactory with the given input stream,
* which must be parsable using DOM.
* @param resource the XML resource to load bean definitions from
* @param parentBeanFactory parent bean factory
* @throws BeansException in case of loading or parsing errors
*/
public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {
//我们再去父类的构造方法中看看，构造方法中实现了哪些功能
super(parentBeanFactory);
//通过 XmlBeanDefinitionReader进行加载资源
this.reader.loadBeanDefinitions(resource);
}
}
- XmlBeanFactory构造函数中，首先要调用父类的构造方法，我们一路走下去，最终走到AbstractAutowireCapableBeanFactory中
- 在AbstractAutowireCapableBeanFactory中，ignoreDependencyInterface方法设置了一些类，分别是BeanNameAware、BeanFactoryAware、BeanClassLoaderAware
2.ignoreDependencyInterface方法，就是将参数中的类添加到集合ignoredDependencyInterfaces中
public AbstractAutowireCapableBeanFactory() {
super();
ignoreDependencyInterface(BeanNameAware.class);
ignoreDependencyInterface(BeanFactoryAware.class);
ignoreDependencyInterface(BeanClassLoaderAware.class);
}
-
我们再来看下这三个感知接口的类继承关系图
感知接口Aware类继承图 - 通过接口名字Aware，应该能猜到，这些都是感知相关的接口，当bean实现了这些接口，在spring实例化bean的时候，就可以通过感知接口中的方法注入相应的数据
- 我们首先通过一个例子来看下，BeanNameAware的作用
public class Student implements BeanNameAware{
private String name="JHXY";
private int age;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "Student{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
@Override
public void setBeanName(String name) {
System.out.println("beanName:" + name);
}
}
applicationContext和之前的配置一样，测试代码
public static void main(String[] args) {
XmlBeanFactory xmlBeanFactory =
new XmlBeanFactory(new ClassPathResource("applicationContext.xml"));
// 从XmlBeanFactory即：spring容器中，获取student bean
Student student = (Student) xmlBeanFactory.getBean("student");
System.out.println(student.getName());
}
测试结果
BeanNameAware感知接口测试结果
- 通过测试结果可以看到，BeanNameAware中的setBeanName方法被调用，并且bean name就是我们在zpplicationContext中配置的Student 的id的属性值，student
- 那现在有个疑问，为什么Student实现了BeanNameAware接口之后，setBeanName方法就会被调用？setBeanName什么时候被调用，调用之后为什么就能拿到beanName？不着急，我们继续看
- ignoreDependencyInterface方法是干什么的？通过注释我们可以知道,在自动装配的时候，忽略指定的接口依赖
/**
* Ignore the given dependency interface for autowiring.
* This will typically be used by application contexts to register
* dependencies that are resolved in other ways, like BeanFactory through
* BeanFactoryAware or ApplicationContext through ApplicationContextAware.
*
By default, only the BeanFactoryAware interface is ignored.
* For further types to ignore, invoke this method for each type.
* @see org.springframework.beans.factory.BeanFactoryAware
* @see org.springframework.context.ApplicationContextAware
*/
public void ignoreDependencyInterface(Class ifc) {
this.ignoredDependencyInterfaces.add(ifc);
}
- 我们顺藤摸瓜，看看ignoredDependencyInterfaces集合在哪里被调用，如下代码
根据注释，一个bean的属性，是否要从依赖排查中剔除，这句话什么意思呢？
也就是说，我们一个bean的某个属性，是否要被注入对应的依赖，还要看一下你这个属性对应的类是否实现了BeanNameAware、BeanFactoryAware、BeanClassLoaderAware这些接口
/**
* Determine whether the given bean property is excluded from dependency checks.
* This implementation excludes properties defined by CGLIB and
* properties whose type matches an ignored dependency type or which
* are defined by an ignored dependency interface.
* @param pd the PropertyDescriptor of the bean property
* @return whether the bean property is excluded
* @see #ignoreDependencyType(Class)
* @see #ignoreDependencyInterface(Class)
*/
protected boolean isExcludedFromDependencyCheck(PropertyDescriptor pd) {
return (AutowireUtils.isExcludedFromDependencyCheck(pd) ||
this.ignoredDependencyTypes.contains(pd.getPropertyType()) ||
AutowireUtils.isSetterDefinedInInterface(pd, this.ignoredDependencyInterfaces));
}
我们继续向下看AutowireUtils.isSetterDefinedInInterface()
在isSetterDefinedInInterface方法中
1.bean对应的属性，是否实现了BeanNameAware、BeanFactoryAware、BeanClassLoaderAware
2.bean属性对应的setter方法，在这三个感知接口中是否也有相同的方法
如果满足以上两种情况，isSetterDefinedInInterface就会返回true,spring在自动装配这个bean时，就不会为这个属性注入值
image.png
- 我们还是通过一个案例来看下
public class BeanNameAwareTest implements BeanNameAware {
private String beanName;
public String getBeanName() {
return beanName;
}
@Override
public void setBeanName(String beanName) {
this.beanName = beanName;
}
}
我们将属性设置为beanName,且该类实现了BeanNameAware接口，这样，setBeanName方法即是beanName的setter方法，且在感知接口中也有setBeanName方法
满足了这两个条件之后，spring就不会为bean beanNameAwareTest的属性beanName注入任何值
我们为属性beanName设置了属性值“beanName”,我们通过测试结果来看下“beanName”这个值能否注入到bean beanNameAwareTest对应的beanName属性中
public static void main(String[] args) {
XmlBeanFactory xmlBeanFactory =
new XmlBeanFactory(new ClassPathResource("applicationContext.xml"));
BeanNameAwareTest beanNameAwareTest = (BeanNameAwareTest) xmlBeanFactory.getBean("beanNameAwareTest");
System.out.println(beanNameAwareTest.getBeanName());
}
测试结果
可以看到，我们设置的beanName的属性并没有变成"beanName"，拿到的依旧是beanNameAwareTest，所以说，如果一个bean实现了BeanNameAware、BeanFactoryAware、BeanClassLoaderAware的话，并且想通过spring自动装配给属性赋值，那么属性的setter方法，就不能和感知接口中的setter方法相同。
spring这样设计，主要是想，如果实现了BeanNameAware,对应的beanName属性值,就应该是这个bean在spring容器中的名字，此时，如果我们从外部xml或者注解中，注入一个新的bean的名称，spring默认就会忽略掉外部注入的名称，确保bean的名称唯一
image.png
OK
我们接着向下看初始化spring容器的逻辑
- XmlBeanDefinitionReader如何加载资源,这里我们可以看到，会将Resource封装成EncodedResource
/**
* Load bean definitions from the specified XML file.
* @param resource the resource descriptor for the XML file
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
*/
@Override
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
//将Resource封装太EncodedResource
return loadBeanDefinitions(new EncodedResource(resource));
}
- 我们看下EncodedResource部分关键源码
public class EncodedResource implements InputStreamSource {
//这里的resource是跟资源有关的
private final Resource resource;
//编码
@Nullable
private final String encoding;
//字符集
@Nullable
private final Charset charset;
/**
* Create a new {@code EncodedResource} for the given {@code Resource},
* not specifying an explicit encoding or {@code Charset}.
* @param resource the {@code Resource} to hold (never {@code null})
*/
//构造方法中，除了资源resource不为空，编码和字符集都为空
public EncodedResource(Resource resource) {
this(resource, null, null);
}
/**
* Open a {@code java.io.Reader} for the specified resource, using the specified
* {@link #getCharset() Charset} or {@linkplain #getEncoding() encoding}
* (if any).
* @throws IOException if opening the Reader failed
* @see #requiresReader()
* @see #getInputStream()
*/
//通过上面的构造方法可知，默认charset和encoding为null，所以getReader(),根据资源获取resource的输入流
public Reader getReader() throws IOException {
if (this.charset != null) {
return new InputStreamReader(this.resource.getInputStream(), this.charset);
}
else if (this.encoding != null) {
return new InputStreamReader(this.resource.getInputStream(), this.encoding);
}
else {
return new InputStreamReader(this.resource.getInputStream());
}
}
// 省略部分代码.....
- 接着loadBeanDefinitions继续向下看
/**
* Load bean definitions from the specified XML file.
* @param encodedResource the resource descriptor for the XML file,
* allowing to specify an encoding to use for parsing the file
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
*/
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
Assert.notNull(encodedResource, "EncodedResource must not be null");
if (logger.isTraceEnabled()) {
logger.trace("Loading XML bean definitions from " + encodedResource);
}
Set currentResources = this.resourcesCurrentlyBeingLoaded.get();
if (!currentResources.add(encodedResource)) {
throw new BeanDefinitionStoreException(
"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
}
//获取EncodedResource的输入流
try (InputStream inputStream = encodedResource.getResource().getInputStream()) {
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
//正式开始加载资源
return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"IOException parsing XML document from " + encodedResource.getResource(), ex);
}
finally {
currentResources.remove(encodedResource);
if (currentResources.isEmpty()) {
this.resourcesCurrentlyBeingLoaded.remove();
}
}
}
/**
* Actually load bean definitions from the specified XML file.
* @param inputSource the SAX InputSource to read from
* @param resource the resource descriptor for the XML file
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
* @see #doLoadDocument
* @see #registerBeanDefinitions
*/
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
//将传进来的inputSource和resource，封装成Document对象
Document doc = doLoadDocument(inputSource, resource);
//解析document对象，并将解析的bean注入到spring中
int count = registerBeanDefinitions(doc, resource);
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + count + " bean definitions from " + resource);
}
return count;
}
catch (BeanDefinitionStoreException ex) {
throw ex;
}
catch (SAXParseException ex) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(),
"Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex);
}
catch (SAXException ex) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(),
"XML document from " + resource + " is invalid", ex);
}
catch (ParserConfigurationException ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"Parser configuration exception parsing XML from " + resource, ex);
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"IOException parsing XML document from " + resource, ex);
}
catch (Throwable ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"Unexpected exception parsing XML document from " + resource, ex);
}
}
/**
* Actually load the specified document using the configured DocumentLoader.
* @param inputSource the SAX InputSource to read from
* @param resource the resource descriptor for the XML file
* @return the DOM Document
* @throws Exception when thrown from the DocumentLoader
* @see #setDocumentLoader
* @see DocumentLoader#loadDocument
*/
protected Document doLoadDocument(InputSource inputSource, Resource resource) throws Exception {
return this.documentLoader.loadDocument(inputSource, getEntityResolver(), this.errorHandler,
getValidationModeForResource(resource), isNamespaceAware());
}
spring在加载的过程中，将XmlBeanDefinitionReader委托给DocumentLoader进行加载
加载xml时，将会按照xml规范和格式进行加载xml中 的bean
结尾
-
受限于篇幅问题，我们下一篇笔记接着学习spring加载XmlBeadFactory
02_spring基础数据准备.jpg