java - 拉取所有带有注解的字段(包括一个对象中的字段在另一个对象中和内部类中的字段)

Question

您好，我正在创建一个自定义 Excel 解析编码器工具，您可以引用这个: How can I call getter/setter for property marked with custom annotation?

我现在需要的是能够找到所有的注解，特别是如何找到嵌套对象或内部类的注解，然后调用那个 setter/getter。

例如:

public class MyOuterClass {
    private InnerClass innerObject;

    public void setInnerObject (InnerClass innerObject) {
        this.innerObject = innerObject;
    }

    public InnerClass getInnerObject() {
        return innerObject;
    }
}

和；

public class InnerClass {

    // I need to get this field and call its setter from the class passed in, so something like:
    // MyOuterClass outClass; outClass.getInnerObject.setFieldIWant("field")
    // OR outClass.getInnerObject.getFieldIWant
    // But have to be able to do at run time, having no knowledge of the class inside
    // This must also work for a nested class

    @ExcelColumn
    private String fieldIWant;

    public void setFieldIWant(String fieldIWant) {
        this.fieldIWant = fieldIWant;
    }

    public String getFieldIWant() {
        return fieldIWant;
    }
}

Answer 1

以下类实现了 AnnotatedElement 接口(interface):

• AccessibleObject
• 类
• 构造函数
• 字段
• 方法
• 包

然后您可以在所述类的对象实例上调用:

<object>.isAnnotationPresent(Class<? extends Annotation> annotationClass)

指定要检查的注释的方法。

因此在您的情况下，@ExcelColumn 的方法调用如下所示:

<object>.isAnnotationPresent(ExcelColumn.class)

然后你可以只使用反射来迭代你想检查的对象的字段/方法等，并在每个对象上调用 .isAnnotationPresent 方法来检查它们是否具有所述注释或不是。

所以如果你想对字段(和嵌套字段)做一些魔术，你可以创建一个像这样的方法:

public void doMagicToFields(Object someObject){
    // Get all declared fields.
    Field[] fields = someObject.getClass().getDeclaredFields();
    for(Field field: fields){
        // If the field is annotated by @ExcelColumn
        if(field.isAnnotationPresent(ExcelColumn.class){
            // If the field is a String (add more checks as needed)
            if(String.class.equals(field.getType()){
                // Set the fields value to "myValue" in case of String.
                field.set(someObject, "myValue");
            }
            // Recursive call to check the nested fields of this field object.
            doMagicToFields(
                // We actually get the field object here.
                field.get(someObject)
            );
        }

    }
}