聊聊Spring中的数据绑定 --- WebDataBinder、ServletRequestDataBinder、WebBindingInitializer...【享学Spring】（下）

// @since 3.1   注意：WebDataBinder 可是1.2就有了~
public interface WebDataBinderFactory {
  // 此处使用的是Spring自己的NativeWebRequest   后面两个参数就不解释了
  WebDataBinder createBinder(NativeWebRequest webRequest, @Nullable Object target, String objectName) throws Exception;
}

public class DefaultDataBinderFactory implements WebDataBinderFactory {
  @Nullable
  private final WebBindingInitializer initializer;
  // 注意：这是唯一构造函数
  public DefaultDataBinderFactory(@Nullable WebBindingInitializer initializer) {
    this.initializer = initializer;
  }
  // 实现接口的方法
  @Override
  @SuppressWarnings("deprecation")
  public final WebDataBinder createBinder(NativeWebRequest webRequest, @Nullable Object target, String objectName) throws Exception {
    WebDataBinder dataBinder = createBinderInstance(target, objectName, webRequest);
    // 可见WebDataBinder 创建好后，此处就会回调（只有一个）
    if (this.initializer != null) {
      this.initializer.initBinder(dataBinder, webRequest);
    }
    // 空方法 子类去实现，比如InitBinderDataBinderFactory实现了词方法
    initBinder(dataBinder, webRequest);
    return dataBinder;
  }
  //  子类可以复写，默认实现是WebRequestDataBinder
  // 比如子类ServletRequestDataBinderFactory就复写了，使用的new ExtendedServletRequestDataBinder(target, objectName)
  protected WebDataBinder createBinderInstance(@Nullable Object target, String objectName, NativeWebRequest webRequest) throws Exception 
    return new WebRequestDataBinder(target, objectName);
  }
}

// @since 3.1
public class InitBinderDataBinderFactory extends DefaultDataBinderFactory {
  // 需要注意的是：`@InitBinder`可以标注N多个方法~  所以此处是List
  private final List<InvocableHandlerMethod> binderMethods;
  // 此子类的唯一构造函数
  public InitBinderDataBinderFactory(@Nullable List<InvocableHandlerMethod> binderMethods, @Nullable WebBindingInitializer initializer) {
    super(initializer);
    this.binderMethods = (binderMethods != null ? binderMethods : Collections.emptyList());
  }
  // 上面知道此方法的调用方法生initializer.initBinder之后
  // 所以使用注解它生效的时机是在直接实现接口的后面的~
  @Override
  public void initBinder(WebDataBinder dataBinder, NativeWebRequest request) throws Exception {
    for (InvocableHandlerMethod binderMethod : this.binderMethods) {
      // 判断@InitBinder是否对dataBinder持有的target对象生效~~~（根据name来匹配的）
      if (isBinderMethodApplicable(binderMethod, dataBinder)) {
        // 关于目标方法执行这块，可以参考另外一篇@InitBinder的原理说明~
        Object returnValue = binderMethod.invokeForRequest(request, null, dataBinder);
        // 标注@InitBinder的方法不能有返回值
        if (returnValue != null) {
          throw new IllegalStateException("@InitBinder methods must not return a value (should be void): " + binderMethod);
        }
      }
    }
  }
  //@InitBinder有个Value值，它是个数组。它是用来匹配dataBinder.getObjectName()是否匹配的   若匹配上了，现在此注解方法就会生效
  // 若value为空，那就对所有生效~~~
  protected boolean isBinderMethodApplicable(HandlerMethod initBinderMethod, WebDataBinder dataBinder) {
    InitBinder ann = initBinderMethod.getMethodAnnotation(InitBinder.class);
    Assert.state(ann != null, "No InitBinder annotation");
    String[] names = ann.value();
    return (ObjectUtils.isEmpty(names) || ObjectUtils.containsElement(names, dataBinder.getObjectName()));
  }
}

// @since 3.1
public class ServletRequestDataBinderFactory extends InitBinderDataBinderFactory {
  public ServletRequestDataBinderFactory(@Nullable List<InvocableHandlerMethod> binderMethods, @Nullable WebBindingInitializer initializer) {
    super(binderMethods, initializer);
  }
  @Override
  protected ServletRequestDataBinder createBinderInstance(
      @Nullable Object target, String objectName, NativeWebRequest request) throws Exception  {
    return new ExtendedServletRequestDataBinder(target, objectName);
  }
}