服务器之家

服务器之家 > 正文

详解Spring中Bean的加载的方法

时间:2020-09-07 09:22     来源/作者:weknow

之前写过bean的解析,这篇来讲讲bean的加载,加载要比bean的解析复杂些,从之前的例子开始.

Spring中加载一个bean的方式:

?
1
TestBean bean = factory.getBean("testBean");

来看看getBean(String name)方法源码,

?
1
2
3
4
@Override
public Object getBean(String name) throws BeansException {
  return doGetBean(name, null, null, false);
}

该getBean(String name)方法位于AbstractBeanFactory抽象类中,AbstractBeanFactory与XmlBeanFactory类关系可以看下图:

详解Spring中Bean的加载的方法

接下去跟进doGetBean()方法源码:

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
protected <T> T doGetBean(
    final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
    throws BeansException {
  // 提取beanName
  final String beanName = transformedBeanName(name);
  Object bean;
 
  // 试着从缓存或实例工厂中获取
  Object sharedInstance = getSingleton(beanName);
  if (sharedInstance != null && args == null) {
    if (logger.isDebugEnabled()) {
      if (isSingletonCurrentlyInCreation(beanName)) {
        logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
            "' that is not fully initialized yet - a consequence of a circular reference");
      }
      else {
        logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
      }
    }
    // 返回实例,有时存在如BeanFactory这样情况时并不是直接返回实例本身而是返回指定方法返回的实例
    bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
  }
 
  else {
    // Fail if we're already creating this bean instance:
    // We're assumably within a circular reference.
    if (isPrototypeCurrentlyInCreation(beanName)) {
      throw new BeanCurrentlyInCreationException(beanName);
    }
 
    // Check if bean definition exists in this factory.
    BeanFactory parentBeanFactory = getParentBeanFactory();
    // 如果在所有已经加载的类中没有beanName则会尝试从parentBeanFactory中检测
    if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
      // Not found -> check parent.
      String nameToLookup = originalBeanName(name);
      // 到BeanFactory查找
      if (args != null) {
        // Delegation to parent with explicit args.
        return (T) parentBeanFactory.getBean(nameToLookup, args);
      }
      else {
        // No args -> delegate to standard getBean method.
        return parentBeanFactory.getBean(nameToLookup, requiredType);
      }
    }
    // 如果不是只做类型检查则是创建bean
    if (!typeCheckOnly) {
      markBeanAsCreated(beanName);
    }
 
    try {
      // 将存储XML配置文件的GernericBeanDefinition转换成RootBeanDefinition,如果BeanName是子Bean的话会合并父类的相关属性
      final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
      checkMergedBeanDefinition(mbd, beanName, args);
 
      // Guarantee initialization of beans that the current bean depends on.
      String[] dependsOn = mbd.getDependsOn();
      // 如果存在依赖的话要递归实例化依赖的bean
      if (dependsOn != null) {
        for (String dependsOnBean : dependsOn) {
          if (isDependent(beanName, dependsOnBean)) {
            throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                "Circular depends-on relationship between '" + beanName + "' and '" + dependsOnBean + "'");
          }
          registerDependentBean(dependsOnBean, beanName);
          getBean(dependsOnBean);
        }
      }
 
      // Create bean instance.
      // 依赖的bean实例化完后就可以实例化mbd了
      if (mbd.isSingleton()) {
        sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
          @Override
          public Object getObject() throws BeansException {
            try {
              return createBean(beanName, mbd, args);
            }
            catch (BeansException ex) {
              // Explicitly remove instance from singleton cache: It might have been put there
              // eagerly by the creation process, to allow for circular reference resolution.
              // Also remove any beans that received a temporary reference to the bean.
              destroySingleton(beanName);
              throw ex;
            }
          }
        });
        bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
      }
 
      else if (mbd.isPrototype()) {
        // It's a prototype -> create a new instance.
        Object prototypeInstance = null;
        try {
          beforePrototypeCreation(beanName);
          prototypeInstance = createBean(beanName, mbd, args);
        }
        finally {
          afterPrototypeCreation(beanName);
        }
        bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
      }
 
      else {
        // 在对应的scope上实例化bean
        String scopeName = mbd.getScope();
        final Scope scope = this.scopes.get(scopeName);
        if (scope == null) {
          throw new IllegalStateException("No Scope registered for scope '" + scopeName + "'");
        }
        try {
          Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {
            @Override
            public Object getObject() throws BeansException {
              beforePrototypeCreation(beanName);
              try {
                return createBean(beanName, mbd, args);
              }
              finally {
                afterPrototypeCreation(beanName);
              }
            }
          });
          bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
        }
        catch (IllegalStateException ex) {
          throw new BeanCreationException(beanName,
              "Scope '" + scopeName + "' is not active for the current thread; " +
              "consider defining a scoped proxy for this bean if you intend to refer to it from a singleton",
              ex);
        }
      }
    }
    catch (BeansException ex) {
      cleanupAfterBeanCreationFailure(beanName);
      throw ex;
    }
  }
 
  // 检查需要的类型是否符合实例bean的实际类型
  if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
    try {
      return getTypeConverter().convertIfNecessary(bean, requiredType);
    }
    catch (TypeMismatchException ex) {
      if (logger.isDebugEnabled()) {
        logger.debug("Failed to convert bean '" + name + "' to required type [" +
            ClassUtils.getQualifiedName(requiredType) + "]", ex);
      }
      throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
    }
  }
  return (T) bean;
}

整个bean加载的过程步骤相对繁琐,主要步骤有以下几点:

1、转换beanName

要知道平时开发中传入的参数name可能只是别名,也可能是FactoryBean,所以需要进行解析转换,一般会进行以下解析:

(1)消除修饰符,比如name="&test",会去除&使name="test";

(2)取alias表示的最后的beanName,比如别名test01指向名称为test02的bean则返回test02。

2、从缓存中加载实例

实例在Spring的同一个容器中只会被创建一次,后面再想获取该bean时,就会尝试从缓存中获取;如果获取不到的话再从singletonFactories中加载。

3、实例化bean

缓存中记录的bean一般只是最原始的bean状态,这时就需要对bean进行实例化。如果得到的是bean的原始状态,但又要对bean进行处理,这时真正需要的是工厂bean中定义的factory-method方法中返回的bean,上面源码中的getObjectForBeanInstance就是来完成这个工作的。

4、检测parentBeanFacotory

从源码可以看出如果缓存中没有数据会转到父类工厂去加载,源码中的!containsBeanDefinition(beanName)就是检测如果当前加载的xml配置文件中不包含beanName所对应的配置,就只能到parentBeanFacotory去尝试加载bean。

5、存储XML配置文件的GernericBeanDefinition转换成RootBeanDefinition之前的文章介绍过XML配置文件中读取到的bean信息是存储在GernericBeanDefinition中的,但Bean的后续处理是针对于RootBeanDefinition的,所以需要转换后才能进行后续操作。

6、初始化依赖的bean

这里应该比较好理解,就是bean中可能依赖了其他bean属性,在初始化bean之前会先初始化这个bean所依赖的bean属性。

7、创建bean

Spring容器根据不同scope创建bean实例。

整个流程就是如此,下面会讲解一些重要步骤的源码。

上面有提到,单例在Spring中的同一容器中只会被创建一次,后面再获取bean的话会直接从缓存中获取,这里是尝试加载,先从缓存中加载,再次就是从singletonFactories中加载;因为在bean中可能会在依赖注入,要避免循环依赖,Spring创建bean时会不等bean创建完成就会将创建该bean的ObjectFactory提前曝光加入到缓存中,但下一个bean创建时要依赖上个bean的话,就直接使用ObjectFacotry。

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
@Override
public Object getSingleton(String beanName) {
  return getSingleton(beanName, true); // true表示允许早期依赖
}
 
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
  // 尝试从缓存获取实例
  Object singletonObject = this.singletonObjects.get(beanName);
  if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
    synchronized (this.singletonObjects) {
      // 若该bean正在加载则不处理
      singletonObject = this.earlySingletonObjects.get(beanName);
      if (singletonObject == null && allowEarlyReference) {
        ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
        if (singletonFactory != null) {
          singletonObject = singletonFactory.getObject();
          // 存入到缓存中
          this.earlySingletonObjects.put(beanName, singletonObject);
          this.singletonFactories.remove(beanName);
        }
      }
    }
  }
  return (singletonObject != NULL_OBJECT ? singletonObject : null);
}
/* 这两个方法在DefaultSingletonBeanRegistry类中 */

从源码可以看出这个方法先尝试从singletonObjects中获取实例,如果获取不到值就从earlySingletonObject中去获取,如果再获取不到的话则到singletonFactories里获取beanName对应的ObjectFactory,再调用这个ObjectFactory的getObject来创建bean,并放到earlySingletonObject中,并且从singletonFactories里remove掉这个ObjectFactory。这里有几个存储bean的不同map:

  1. -singletonObjects:保存BeanName和创建bean实例之间的关系。
  2. -singletonFactories:保存BeanName和创建bean实例的工厂之间的关系。
  3. -earlySingletonObject:保存BeanName和创建bean实例之间的关系,与-singletonObjects不同的是当一个单例bean被放到里面后,那当bean在创建过程中,就可以通过getBean方法获取到,可以用来检测循环引用。
  4. -registeredSingletons:保存当前所有已注册的bean。

如果上面缓存中不存在已经加载的单例bean就要重新开始bean的加载过程了,Spring中使用getSingleton重载方法实现bean的加载过程。

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
  Assert.notNull(beanName, "'beanName' must not be null");
  synchronized (this.singletonObjects) {
    // 先检查bean是否已经加载
    Object singletonObject = this.singletonObjects.get(beanName);
    // 如果空才进行singleton的bean的初始化
    if (singletonObject == null) {
      if (this.singletonsCurrentlyInDestruction) {
        throw new BeanCreationNotAllowedException(beanName,
            "Singleton bean creation not allowed while the singletons of this factory are in destruction " +
            "(Do not request a bean from a BeanFactory in a destroy method implementation!)");
      }
      if (logger.isDebugEnabled()) {
        logger.debug("Creating shared instance of singleton bean '" + beanName + "'");
      }
      beforeSingletonCreation(beanName);
      boolean newSingleton = false;
      boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
      if (recordSuppressedExceptions) {
        this.suppressedExceptions = new LinkedHashSet<Exception>();
      }
      try {
        // 初始化bean
        singletonObject = singletonFactory.getObject();
        newSingleton = true;
      }
      catch (IllegalStateException ex) {
        // Has the singleton object implicitly appeared in the meantime ->
        // if yes, proceed with it since the exception indicates that state.
        singletonObject = this.singletonObjects.get(beanName);
        if (singletonObject == null) {
          throw ex;
        }
      }
      catch (BeanCreationException ex) {
        if (recordSuppressedExceptions) {
          for (Exception suppressedException : this.suppressedExceptions) {
            ex.addRelatedCause(suppressedException);
          }
        }
        throw ex;
      }
      finally {
        if (recordSuppressedExceptions) {
          this.suppressedExceptions = null;
        }
        afterSingletonCreation(beanName);
      }
      if (newSingleton) {
        // 存入缓存
        addSingleton(beanName, singletonObject);
      }
    }
    return (singletonObject != NULL_OBJECT ? singletonObject : null);
  }
}

这段代码使用了回调方法,使程序可以在单例创建的前后做一些准备及处理操作,真正的获取单例bean的方法其实并不是在这个方法实现的,而是在ObjectFactory类型的实例singletonFactory中实现的。

下面准备创建bean

看看createBean()方法源码(该方法在AbstractAutowireCapableBeanFactory类中):

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
protected Object createBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
    throws BeanCreationException {
 
  if (logger.isDebugEnabled()) {
    logger.debug("Creating instance of bean '" + beanName + "'");
  }
  // 锁定class,根据设置的class属性或根据className来解析Class
  resolveBeanClass(mbd, beanName);
 
  // 验证和准备覆盖的方法
  try {
    mbd.prepareMethodOverrides();
  }
  catch (BeanDefinitionValidationException ex) {
    throw new BeanDefinitionStoreException(mbd.getResourceDescription(),
        beanName, "Validation of method overrides failed", ex);
  }
 
  try {
    // 用BeanPostProcessors返回代理来替代真正的实例
    Object bean = resolveBeforeInstantiation(beanName, mbd);
    if (bean != null) {
      return bean;
    }
  }
  catch (Throwable ex) {
    throw new BeanCreationException(mbd.getResourceDescription(), beanName,
        "BeanPostProcessor before instantiation of bean failed", ex);
  }
 
  Object beanInstance = doCreateBean(beanName, mbd, args);
  if (logger.isDebugEnabled()) {
    logger.debug("Finished creating instance of bean '" + beanName + "'");
  }
  return beanInstance;
}

从createBean()方法源码可以看出主要做了以下操作:

  1. 根据设置的class属性或根据className来解析Class;
  2. 对覆盖进行标记并验证,在Spring配置中是存在lookup-mothod和replace-method的,这两个配置的加载其实就是将配置统一存放在BeanDefinition中的methodOverrides属性里,这个方法的操作也就是针对于这两个配置的;
  3. 应用初始化前的后处理器,最后创建bean。

在createBean()方法里执行完resolveBeforeInstantiation方法后,如果创建了代理且不为空的话就直接返回,否则需要进行常规bean的创建,这个创建过程是在doCreateBean中完成的,跟进源码:

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) {
  // Instantiate the bean.
  BeanWrapper instanceWrapper = null;
  if (mbd.isSingleton()) {
    instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
  }
  if (instanceWrapper == null) {
    // 根据指定bean使用相应策略创建实例
    instanceWrapper = createBeanInstance(beanName, mbd, args);
  }
  final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
  Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);
 
  // Allow post-processors to modify the merged bean definition.
  synchronized (mbd.postProcessingLock) {
    if (!mbd.postProcessed) {
      applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
      mbd.postProcessed = true;
    }
  }
 
  // 检测循环依赖,是否需要提早曝光
  boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
      isSingletonCurrentlyInCreation(beanName));
  if (earlySingletonExposure) {
    if (logger.isDebugEnabled()) {
      logger.debug("Eagerly caching bean '" + beanName +
          "' to allow for resolving potential circular references");
    }
    // 避免循环依赖,可以在bean初始化完成前将创建实例的ObjectFactory加入工厂
    addSingletonFactory(beanName, new ObjectFactory<Object>() {
      @Override
      public Object getObject() throws BeansException {
        // 对bean再次依赖引用
        // AOP也是在这里将advice动态织入bean中,若没有则直接返回bean,不做处理
        return getEarlyBeanReference(beanName, mbd, bean);
      }
    });
  }
 
  // Initialize the bean instance.
  Object exposedObject = bean;
  try {
    // 填充bean,注入属性值,如果存在依赖于其他bean的属性,会递归初始化
    populateBean(beanName, mbd, instanceWrapper);
    if (exposedObject != null) {
      // 调用初始化方法
      exposedObject = initializeBean(beanName, exposedObject, mbd);
    }
  }
  catch (Throwable ex) {
    if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
      throw (BeanCreationException) ex;
    }
    else {
      throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
    }
  }
 
  if (earlySingletonExposure) {
    Object earlySingletonReference = getSingleton(beanName, false);
    // earlySingletonReference只有在检测到有循环依赖的情况下才会不为空
    if (earlySingletonReference != null) {
      if (exposedObject == bean) {
        exposedObject = earlySingletonReference;
      }
      else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
        String[] dependentBeans = getDependentBeans(beanName);
        Set<String> actualDependentBeans = new LinkedHashSet<String>(dependentBeans.length);
        for (String dependentBean : dependentBeans) {
          // 检测依赖
          if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
            actualDependentBeans.add(dependentBean);
          }
        }
        if (!actualDependentBeans.isEmpty()) {
          throw new BeanCurrentlyInCreationException(beanName,
              "Bean with name '" + beanName + "' has been injected into other beans [" +
              StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
              "] in its raw version as part of a circular reference, but has eventually been " +
              "wrapped. This means that said other beans do not use the final version of the " +
              "bean. This is often the result of over-eager type matching - consider using " +
              "'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
        }
      }
    }
  }
 
  // Register bean as disposable.
  try {
    // 依据scopse注册bean
    registerDisposableBeanIfNecessary(beanName, bean, mbd);
  }
  catch (BeanDefinitionValidationException ex) {
    throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
  }
 
  return exposedObject;
}

上面源码完成的操作可以概括为以下几点:

  1. 开始是单例的话要先清除缓存;
  2. 实例化bean,将BeanDefinition转换为BeanWrapper;
  3. 使用MergedBeanDefinitionPostProcessor,Autowired注解就是通过此方法实现类型的预解析;
  4. 解决循环依赖问题;
  5. 填充属性,将属性填充到bean实例中;
  6. 注册DisposableBean;
  7. 创建完成并返回

接下来创建bean实例,看createBeanInstance()方法:

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, Object[] args) {
  // 解析class
  Class<?> beanClass = resolveBeanClass(mbd, beanName);
 
  if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {
    throw new BeanCreationException(mbd.getResourceDescription(), beanName,
        "Bean class isn't public, and non-public access not allowed: " + beanClass.getName());
  }
 
  // 若工厂方法不为空则使用工厂方法初始化
  if (mbd.getFactoryMethodName() != null) {
    return instantiateUsingFactoryMethod(beanName, mbd, args);
  }
 
  // Shortcut when re-creating the same bean...
  boolean resolved = false;
  boolean autowireNecessary = false;
  if (args == null) {
    synchronized (mbd.constructorArgumentLock) {
      if (mbd.resolvedConstructorOrFactoryMethod != null) {
        resolved = true;
        autowireNecessary = mbd.constructorArgumentsResolved;
      }
    }
  }
  // 如果已经解析过则使用解析好的构造方法不需要再次锁定
  if (resolved) {
    if (autowireNecessary) {
      // 构造方法自动注入
      return autowireConstructor(beanName, mbd, null, null);
    }
    else {
      // 使用默认构造方法
      return instantiateBean(beanName, mbd);
    }
  }
 
  // 根据参数解析构造方法
  Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
  if (ctors != null ||
      mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_CONSTRUCTOR ||
      mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
    return autowireConstructor(beanName, mbd, ctors, args);
  }
 
  // No special handling: simply use no-arg constructor.
  return instantiateBean(beanName, mbd);
}

可以看出如果在RootBeanDefinition中存在factoryMethodName属性,或者说配置文件中配置了factory-method,那么Spring会尝试使用instantiateUsingFactoryMethod(beanName, mbd, args)方法根据RootBeanDefinition中的配置生成bean实例。

再解析构造方法并进行实例化,Spring会根据参数及类型判断使用哪个构造方法再进行实例化。判断调用哪个构造方法的过程会采用缓存机制,如果已经解析过则不需要重复解析而是从RootBeanDefinition中的属性resolvedConstructorOrFactoryMethod缓存的值去取,不然则需要再次解析。

创建bean后接下来就进行属性注入,属性注入的操作在populateBean()方法中,跟进源码:

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
  PropertyValues pvs = mbd.getPropertyValues();
 
  if (bw == null) {
    if (!pvs.isEmpty()) {
      throw new BeanCreationException(
          mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
    }
    else {
      // Skip property population phase for null instance.
      return;
    }
  }
 
  // Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
  // state of the bean before properties are set. This can be used, for example,
  // to support styles of field injection.
  boolean continueWithPropertyPopulation = true;
 
  if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
    for (BeanPostProcessor bp : getBeanPostProcessors()) {
      if (bp instanceof InstantiationAwareBeanPostProcessor) {
        InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
        if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
          continueWithPropertyPopulation = false;
          break;
        }
      }
    }
  }
 
  if (!continueWithPropertyPopulation) {
    return;
  }
 
  if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
      mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
    MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
 
    // Add property values based on autowire by name if applicable.
    if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
      autowireByName(beanName, mbd, bw, newPvs);
    }
 
    // Add property values based on autowire by type if applicable.
    if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
      autowireByType(beanName, mbd, bw, newPvs);
    }
 
    pvs = newPvs;
  }
 
  boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
  boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE);
 
  if (hasInstAwareBpps || needsDepCheck) {
    PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
    if (hasInstAwareBpps) {
      for (BeanPostProcessor bp : getBeanPostProcessors()) {
        if (bp instanceof InstantiationAwareBeanPostProcessor) {
          InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
          pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
          if (pvs == null) {
            return;
          }
        }
      }
    }
    if (needsDepCheck) {
      checkDependencies(beanName, mbd, filteredPds, pvs);
    }
  }
 
  applyPropertyValues(beanName, mbd, bw, pvs);
}

在populateBean方法的中的主要处理流程:

  1. InstantiationAwareBeanPostProcessor处理器的postProcessAfterInstantiation方法控制程序是否继续填充属性;
  2. 根据注入类型提取依赖的bean,并存入PropertyValues中;
  3. 应用InstantiationAwareBeanPostProcessor处理器的postProcessPropertyValues方法对属性在填充前再次处理,主要还是验证属性;
  4. 将所有PropertyValues中的属性填充到BeanWrapper中。

最后初始化bean

学过Spring的都知道bean配置时有一个init-method属性,这个属性的作用是在bean实例化前调用init-method指定的方法进行需要的实例化操作,现在就进入这个方法了;Spring中程序已经执行过bean的实例化,并且进行了属性的填充,而就在这时将会调用用户设定的初始化方法。

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
  if (System.getSecurityManager() != null) {
    AccessController.doPrivileged(new PrivilegedAction<Object>() {
      @Override
      public Object run() {
        invokeAwareMethods(beanName, bean);
        return null;
      }
    }, getAccessControlContext());
  }
  else {
    // 特殊bean处理
    invokeAwareMethods(beanName, bean);
  }
 
  Object wrappedBean = bean;
  if (mbd == null || !mbd.isSynthetic()) {
    wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
  }
 
  try {
    invokeInitMethods(beanName, wrappedBean, mbd);
  }
  catch (Throwable ex) {
    throw new BeanCreationException(
        (mbd != null ? mbd.getResourceDescription() : null),
        beanName, "Invocation of init method failed", ex);
  }
 
  if (mbd == null || !mbd.isSynthetic()) {
    wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
  }
  return wrappedBean;
}

最后加载完Bean并执行完初始化操作后,一个bean的加载基本就结束了。

以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持服务器之家。

原文链接:http://www.jianshu.com/p/5fd1922ccab1

标签:

相关文章

热门资讯

2020微信伤感网名听哭了 让对方看到心疼的伤感网名大全
2020微信伤感网名听哭了 让对方看到心疼的伤感网名大全 2019-12-26
Intellij idea2020永久破解,亲测可用!!!
Intellij idea2020永久破解,亲测可用!!! 2020-07-29
歪歪漫画vip账号共享2020_yy漫画免费账号密码共享
歪歪漫画vip账号共享2020_yy漫画免费账号密码共享 2020-04-07
最新idea2020注册码永久激活(激活到2100年)
最新idea2020注册码永久激活(激活到2100年) 2020-07-29
电视剧《琉璃》全集在线观看 琉璃美人煞1-59集免费观看地址
电视剧《琉璃》全集在线观看 琉璃美人煞1-59集免费观看地址 2020-08-12
返回顶部