聊聊Spring中的数据绑定 --- BeanWrapper以及Java内省Introspector和PropertyDescriptor【享学Spring】（上）

//@since 13 April 2001  很清晰的看到，它也是个`PropertyAccessor`属性访问器
public interface BeanWrapper extends ConfigurablePropertyAccessor {
  // @since 4.1
  void setAutoGrowCollectionLimit(int autoGrowCollectionLimit);
  int getAutoGrowCollectionLimit();
  Object getWrappedInstance();
  Class<?> getWrappedClass();
  // 获取属性们的PropertyDescriptor  获取属性们
  PropertyDescriptor[] getPropertyDescriptors();
  // 获取具体某一个属性~
  PropertyDescriptor getPropertyDescriptor(String propertyName) throws InvalidPropertyException;
}

public class BeanWrapperImpl extends AbstractNestablePropertyAccessor implements BeanWrapper {
  // 缓存内省结果~
  @Nullable
  private CachedIntrospectionResults cachedIntrospectionResults;
  // The security context used for invoking the property methods.
  @Nullable
  private AccessControlContext acc;
  // 构造方法都是沿用父类的~
  public BeanWrapperImpl() {
    this(true);
  }
  ... 
  private BeanWrapperImpl(Object object, String nestedPath, BeanWrapperImpl parent) {
    super(object, nestedPath, parent);
    setSecurityContext(parent.acc);
  }
  // @since 4.3  设置目标对象~~~
  public void setBeanInstance(Object object) {
    this.wrappedObject = object;
    this.rootObject = object;
    this.typeConverterDelegate = new TypeConverterDelegate(this, this.wrappedObject);
    // 设置内省的clazz
    setIntrospectionClass(object.getClass());
  }
  // 复写父类的方法  增加内省逻辑
  @Override
  public void setWrappedInstance(Object object, @Nullable String nestedPath, @Nullable Object rootObject) {
    super.setWrappedInstance(object, nestedPath, rootObject);
    setIntrospectionClass(getWrappedClass());
  }
  // 如果cachedIntrospectionResults它持有的BeanClass并不是传入的clazz 那就清空缓存 重新来~~~
  protected void setIntrospectionClass(Class<?> clazz) {
    if (this.cachedIntrospectionResults != null && this.cachedIntrospectionResults.getBeanClass() != clazz) {
      this.cachedIntrospectionResults = null;
    }
  }
  private CachedIntrospectionResults getCachedIntrospectionResults() {
    if (this.cachedIntrospectionResults == null) {
      // forClass此方法：生成此clazz的类型结果，并且缓存了起来~~
      this.cachedIntrospectionResults = CachedIntrospectionResults.forClass(getWrappedClass());
    }
    return this.cachedIntrospectionResults;
  }
  ...
  // 获取到此属性的处理器。此处是个BeanPropertyHandler 内部类~
  @Override
  @Nullable
  protected BeanPropertyHandler getLocalPropertyHandler(String propertyName) {
    PropertyDescriptor pd = getCachedIntrospectionResults().getPropertyDescriptor(propertyName);
    return (pd != null ? new BeanPropertyHandler(pd) : null);
  }
  @Override
  protected BeanWrapperImpl newNestedPropertyAccessor(Object object, String nestedPath) {
    return new BeanWrapperImpl(object, nestedPath, this);
  }
  @Override
  public PropertyDescriptor[] getPropertyDescriptors() {
    return getCachedIntrospectionResults().getPropertyDescriptors();
  }
  // 获取具体某一个属性的PropertyDescriptor 
  @Override
  public PropertyDescriptor getPropertyDescriptor(String propertyName) throws InvalidPropertyException {
    BeanWrapperImpl nestedBw = (BeanWrapperImpl) getPropertyAccessorForPropertyPath(propertyName);
    String finalPath = getFinalPath(nestedBw, propertyName);
    PropertyDescriptor pd = nestedBw.getCachedIntrospectionResults().getPropertyDescriptor(finalPath);
    if (pd == null) {
      throw new InvalidPropertyException(getRootClass(), getNestedPath() + propertyName, "No property '" + propertyName + "' found");
    }
    return pd;
  }
  ...
  // 此处理器处理的是PropertyDescriptor 
  private class BeanPropertyHandler extends PropertyHandler {
    private final PropertyDescriptor pd;
    // 是否可读、可写  都是由PropertyDescriptor 去决定了~
    // java.beans.PropertyDescriptor~~
    public BeanPropertyHandler(PropertyDescriptor pd) {
      super(pd.getPropertyType(), pd.getReadMethod() != null, pd.getWriteMethod() != null);
      this.pd = pd;
    }
    ...
    @Override
    @Nullable
    public Object getValue() throws Exception {
      ...
      ReflectionUtils.makeAccessible(readMethod);
      return readMethod.invoke(getWrappedInstance(), (Object[]) null);
    }
    ...
  }
}

  // 就这样简单几步，就完成了表单到User对象的封装~
    public void insertUser(HttpServletRequest request) throws Exception {
        User user = new User();
        // 遍历：根据字段名去拿值即可（此处省略判空、类型转换等细节，不在本文讨论范围）
        PropertyDescriptor[] pds = Introspector.getBeanInfo(User.class).getPropertyDescriptors();
        for (PropertyDescriptor pd : pds) {
            pd.getWriteMethod().invoke(user, request.getParameter(pd.getName()));
        }
    }

@Getter
@Setter
@ToString
public class Child {
    private String name;
    private Integer age;
}

    public static void main(String[] args) throws IntrospectionException {
        BeanInfo beanInfo = Introspector.getBeanInfo(Child.class);
        BeanDescriptor beanDescriptor = beanInfo.getBeanDescriptor();
        MethodDescriptor[] methodDescriptors = beanInfo.getMethodDescriptors();
        PropertyDescriptor[] propertyDescriptors = beanInfo.getPropertyDescriptors();
        // 打印
        System.out.println(beanDescriptor);
        System.out.println("------------------------------");
        Arrays.stream(methodDescriptors).forEach(x -> System.out.println(x));
        System.out.println("------------------------------");
        Arrays.stream(propertyDescriptors).forEach(x -> System.out.println(x));
        System.out.println("------------------------------");
    }

java.beans.BeanDescriptor[name=Child; beanClass=class com.fsx.bean.Child]
------------------------------
java.beans.MethodDescriptor[name=getClass; method=public final native java.lang.Class java.lang.Object.getClass()]
java.beans.MethodDescriptor[name=getName; method=public java.lang.String com.fsx.bean.Child.getName()]
java.beans.MethodDescriptor[name=setAge; method=public void com.fsx.bean.Child.setAge(java.lang.Integer)]
java.beans.MethodDescriptor[name=setName; method=public void com.fsx.bean.Child.setName(java.lang.String)]
java.beans.MethodDescriptor[name=getAge; method=public java.lang.Integer com.fsx.bean.Child.getAge()]
java.beans.MethodDescriptor[name=wait; method=public final void java.lang.Object.wait() throws java.lang.InterruptedException]
java.beans.MethodDescriptor[name=notifyAll; method=public final native void java.lang.Object.notifyAll()]
java.beans.MethodDescriptor[name=notify; method=public final native void java.lang.Object.notify()]
java.beans.MethodDescriptor[name=wait; method=public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException]
java.beans.MethodDescriptor[name=hashCode; method=public native int java.lang.Object.hashCode()]
java.beans.MethodDescriptor[name=wait; method=public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException]
java.beans.MethodDescriptor[name=equals; method=public boolean java.lang.Object.equals(java.lang.Object)]
java.beans.MethodDescriptor[name=toString; method=public java.lang.String com.fsx.bean.Child.toString()]
------------------------------
java.beans.PropertyDescriptor[name=age; propertyType=class java.lang.Integer; readMethod=public java.lang.Integer com.fsx.bean.Child.getAge(); writeMethod=public void com.fsx.bean.Child.setAge(java.lang.Integer)]
java.beans.PropertyDescriptor[name=class; propertyType=class java.lang.Class; readMethod=public final native java.lang.Class java.lang.Object.getClass()]
java.beans.PropertyDescriptor[name=name; propertyType=class java.lang.String; readMethod=public java.lang.String com.fsx.bean.Child.getName(); writeMethod=public void com.fsx.bean.Child.setName(java.lang.String)]
------------------------------