笔记：setAccessible方法启用/禁用权限控制检查

class A {

    private int i;

    public int getI(){

       return i;

    }

    private void setI(int i) {

       this.i = i;

    }

}

 Class<?> clazz= Class.forName("hadoopclient.A");

       

       Field iField =clazz.getDeclaredField("i");

       System.out.println("i: "+iField);

       Method getI = clazz.getMethod("getI", newClass[]{});

       System.out.println("getI: "+getI);

       Method setI = clazz.getDeclaredMethod("setI", newClass[]{int.class});

       System.out.println("setI: "+setI);

       

       Object newInstance = clazz.newInstance();

       

       Object returnValue = getI.invoke(newInstance,newClass<?>[]{});

       System.out.println("init: "+returnValue);

       

       setI.setAccessible(true); //若无此句将抛异常

       setI.invoke(newInstance, newObject[]{100});

       returnValue = getI.invoke(newInstance, newClass<?>[]{});

       System.out.println("invokesetI(100): "+returnValue);

        

    }

}

注意：

setAccessible(true)并不是将方法的访问权限改成了public，而是取消java的权限控制检查。所以即使是public方法，其accessible属相默认也是false

JDK 文档：

setAccessible

public void setAccessible(boolean flag)
                   throws SecurityException

Setthe accessible flag forthis object to the indicated boolean value. A valueof true indicates thatthe reflected object should suppress Java language access checkingwhen it is used. A valueof false indicates thatthe reflected object should enforce Java language access checks.

First, if there is a security manager,its checkPermission methodis called witha ReflectPermission("suppressAccessChecks") permission.

A SecurityException israisedif flag is true butaccessibility of this object may not be changed (for example, ifthis element object is a Constructor objectfor the class Class).

A SecurityException israised if this object is a Constructor objectfor the class java.lang.Class,and flag istrue.

Parameters:

flag - the new value forthe accessible flag

Throws:

SecurityException -if the request is denied.

See Also:

SecurityManager.checkPermission(java.security.Permission), RuntimePermission