使用Java反射访问嵌套字段

Question

假设我有几个这样的类：

public class A {
     public B element;
}

public class B {
     public C anotherElement; // where C refers to another type which contains types D, E, F, etc.....
}

我想迭代所有包含的子类（不是继承的），并获得嵌套对象树中所有字段的列表。但是，当我使用这样的反射代码时：

    Field[] myFields = providedObject.getClass().getDeclaredFields();
    for (Field myField : myFields) {
        // do something here?? to access the sub-fields of the class
        // if I print out myField.getName(), I get the element of class A, but I also want to access the anotherElement of class B (without hard-coding the name 'anotherElement', I want a full traversal of all nested fields)
    }

在“do somethine here”步骤中，我想访问myField的子字段，但在Field api中没有看到任何直接允许我这样做的内容。我试过：

MyField.getDeclaringClass（）. getDeclaredFields（）-

和

MyField.get类

那么如何从反射api访问嵌套字段呢？

谢谢。

Answer 1

我添加了以下语句以退出递归方法。你可以随心所欲地改变它。

        if (clazz == null || clazz.isPrimitive() || !clazz.getPackage().getName().startsWith("com.vvv.stack02")) {
            return;
        }

其主要思想是，您需要通过键入以下行将字段转换为类。

Class<?> fieldClass = myField.getType();

public class Main {

    public static void main(String[] args) {
        printFields(A.class);
    }

    public static void printFields(Class<?> clazz) {

        if (clazz == null || clazz.isPrimitive() || !clazz.getPackage().getName().startsWith("com.vvv.stack02")) {
            return;
        }

        Field[] myFields = clazz.getDeclaredFields();
        for (Field myField : myFields) {
            System.out.println(clazz.getSimpleName() + "->" + myField.getType().getSimpleName() + ":" + myField.getName());
            Class<?> fieldClass = myField.getType();
            printField(fieldClass);
        }

    }

    public static class A {
        public B element;
    }

    public static class B {
        public C anotherElement; // where C refers to another type which contains types D, E, F, etc.....
    }

    public static class C {
        public Integer a;
    }

}

Answer 2

这只是一点递归：

public static void traverseDepthFirst(Object obj) { // May need throws/catch!
    if (obj == null) {
        // ... do something for null ...
        return;
    }
    // ... perhaps do something different for arrays, primitives, String, etc.
    for (Field field : obj.getClass().getDeclaredFields()) {
        field.setAccessible(true);
        // ... pre-traversal code ...
        traverseDepthFirst(field.get(obj));
        // ... post-traversal code ...
    }
}

编辑：这将只考虑叶类。包括超级班。

public static void traverseDepthFirst(Object obj) { // May need throws/catch!
    if (obj == null) {
        // ... do something for null ...
        return;
    }
    // ... perhaps do something different for arrays, primitives, String, etc.
    for (
        Class<?> clazz = obj.getClass();
        clazz != null;
        clazz = clazz.getSuperclass()
    ) {
        for (Field field : clazz.getDeclaredFields()) {
            field.setAccessible(true);
            // ... pre-traversal code ...
            traverseDepthFirst(field.get(obj));
            // ... post-traversal code ...
        }
    }
}