使用 Java 反射访问嵌套字段

Question

假设我有几个class这种风格的：

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.....
}

我想遍历所有包含的子classes（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 something here' 这一步，我想访问 myField 的子字段，但我在字段 api 中看不到任何东西可以直接让我这样做。我试过：

myField.getDeclaringClass().getDeclaredFields() -> 这似乎 return 我们已经看到的相同元素，而不是子元素

和

myField.getClass().getDeclaredFields() -> 这似乎 return 'Field' class 的字段而不是我的 class A 或B

那么我如何从反射中访问嵌套字段 api？

谢谢。

Answer 1

我添加了以下语句来退出递归方法。你可以随心所欲地改变它。

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

主要思想是您需要通过键入以下行将字段转换为 class。

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

只是递归了一点：

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： 那只会考虑叶子class。包括超级 classes.

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 ...
        }
    }
}

使用 Java 反射访问嵌套字段

Access Nested Field using Java Reflection

java

reflection

field