java反射 - getXXX 与 getDeclaredXXX

Posted 2020-11-17 Mr.yang.localhost

1、getXXX 和 getDeclaredXXX

java 里 Class<?> 有下面这些方法：

类似的方法有：

2、getMethod(s) 和 getDeclaredMethod(s)

getDeclaredMethods只获取当前对象申明的方法，不包含继承过来的方法

* Returns an array containing {@code Method} objects reflecting all the
* declared methods of the class or interface represented by this {@code
* Class} object, including public, protected, default (package)
* access, and private methods, but excluding inherited methods.

getMethods获取public方法

* Returns an array containing {@code Method} objects reflecting all the
* public methods of the class or interface represented by this {@code
* Class} object, including those declared by the class or interface and
* those inherited from superclasses and superinterfaces.

以常用的getMethod和getDeclaredMethod为例：

public class DemoService {
    public String showDemoPublic(String methodName) {
        return "show demo " + methodName;
    }

    protected String showDemoProtected(String methodName) {
        return "show demo " + methodName;
    }

    private String showDemoPrivate(String methodName) {
        return "show demo " + methodName;
    }
}

getMethods与getDeclaredMethods：

System.out.println("========================getMethods=========================");
Method[] methods_1 = demoService.getClass().getMethods();
for (Method m : methods_1) {
    System.out.println(m);
}

System.out.println("========================getDeclaredMethods=========================");
Method[] methods_2 = demoService.getClass().getDeclaredMethods();
for (Method m : methods_2) {
    System.out.println(m);
}

========================getMethods=========================
public java.lang.String com.logback.demo.service.DemoService.showDemoPublic(java.lang.String)
public final void java.lang.Object.wait() throws java.lang.InterruptedException
public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException
public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException
public boolean java.lang.Object.equals(java.lang.Object)
public java.lang.String java.lang.Object.toString()
public native int java.lang.Object.hashCode()
public final native java.lang.Class java.lang.Object.getClass()
public final native void java.lang.Object.notify()
public final native void java.lang.Object.notifyAll()
========================getDeclaredMethods=========================
public java.lang.String com.logback.demo.service.DemoService.showDemoPublic(java.lang.String)
private java.lang.String com.logback.demo.service.DemoService.showDemoPrivate(java.lang.String)
protected java.lang.String com.logback.demo.service.DemoService.showDemoProtected(java.lang.String)

getMethod与getDeclaredMethod

public void getMethodByName(@RequestParam("method") String method) throws NoSuchMethodException {try {
       System.out.println("========================getMethod=========================");
       Method method1 = demoService.getClass().getMethod("showDemo" + method, String.class);
       System.out.println(method1);
    } catch (Exception ex) {
       System.out.println(ex);
    }
    try {
    　　System.out.println("========================getDeclaredMethod=========================");
    　　Method method2 = demoService.getClass().getDeclaredMethod("showDemo" + method, String.class);
    　　System.out.println(method2);
    } catch (Exception ex) {
    　　System.out.println(ex);
    }
}

http://localhost:8088/getMethod?method=Public

========================getMethod=========================
public java.lang.String com.logback.demo.service.DemoService.showDemoPublic(java.lang.String)
========================getDeclaredMethod=========================
public java.lang.String com.logback.demo.service.DemoService.showDemoPublic(java.lang.String)

http://localhost:8088/getMethod?method=Protected

========================getMethod=========================
java.lang.NoSuchMethodException: com.logback.demo.service.DemoService.showDemoProtected(java.lang.String)
========================getDeclaredMethod=========================
protected java.lang.String com.logback.demo.service.DemoService.showDemoProtected(java.lang.String)

http://localhost:8088/getMethod?method=Private

========================getMethod=========================
java.lang.NoSuchMethodException: com.logback.demo.service.DemoService.showDemoPrivate(java.lang.String)
========================getDeclaredMethod=========================
private java.lang.String com.logback.demo.service.DemoService.showDemoPrivate(java.lang.String)

2、getField(s) 和 getDeclaredField(s)

public class Demo {
　　private Integer id;
　　private String name;
　　public String desc;
}

public class StudentDemo extends Demo {
　　private Integer age;
　　private Integer sex;
}

验证getField和getDeclareField

        for (Field field : demo.getClass().getDeclaredFields()) {
            System.out.println(field);
        }
        System.out.println(">>>>>>>>");
        for (Field field : demo.getClass().getFields()) {
            System.out.println(field);
        }
        System.out.println("===========================================");

        for (Field field : student.getClass().getDeclaredFields()) {
            System.out.println(field);
        }
        System.out.println(">>>>>>>>");
        for (Field field : student.getClass().getFields()) {
            System.out.println(field);
        }

getDeclaredField获取所有申明的属性，不包含继承来的属性。

getFields获取所有public的属性，包含继承来的属性。

private java.lang.Integer com.logback.demo.common.Demo.id

private java.lang.String com.logback.demo.common.Demo.name

public java.lang.String com.logback.demo.common.Demo.desc

>>>>>>>>

public java.lang.String com.logback.demo.common.Demo.desc

===========================================

private java.lang.Integer com.logback.demo.common.StudentDemo.age

private java.lang.Integer com.logback.demo.common.StudentDemo.sex

>>>>>>>>

 

public java.lang.String com.logback.demo.common.Demo.desc