JDK源码/*分析 ：反射包 java.lang.reflect③ 之 Field 获取类的属性字段信息

    今天的主角：java.lang.reflect.Field

    继前面说的，一个类有它的抽象，构造方法有它的抽象，当然我们类中的字段也可以有它的抽象。

Field 也就是我们说的字段，类中的属性。一般地我们在类中看到的样子是这样的：

private String privateStr ;

public static final  String publicStr ;

         String protectStr ;

public static final String finalStr = "110" ;

    从上面可以看出，一个字段对象应该有5部份：字段的权限（private、public、protect）,是否静态是否不可变，字段的类型（String、Date等），字段名，字段值。

获取Field 对象

    Class 对象中获取Field 对象的方法有：

     获取所有权限的字段

    Field    getDeclaredField(String name)

    Field[]    getDeclaredFields()

获取公共权限的字段

    Field    getField(String name)

    Field[]    getFields()

    首先贴上我们的测试pojo类

package com.hlmtest.java.reflect;

public class TestFieldClass {

      private String privateStr ;

      public   String publicStr ;

                String protectStr ;

      public static final String finalStr = "110" ;

     

      public TestFieldClass(){}

     

      public TestFieldClass(String privateStr ,String publicStr ,String protectStr ){

            this . privateStr = privateStr ;

            this . publicStr = publicStr ;

            this . protectStr = protectStr ;

           

     }

      public String getPrivateStr() {

            return privateStr ;

     }

      public void setPrivateStr(String privateStr ) {

            this . privateStr = privateStr ;

     }

      public String getPublicStr() {

            return publicStr ;

     }

      public void setPublicStr(String publicStr ) {

            this . publicStr = publicStr ;

     }

      public String getProtectStr() {

            return protectStr ;

     }

      public void setProtectStr(String protectStr ) {

            this . protectStr = protectStr ;

     }

      public String toString(){

            return "privateStr:" + privateStr + ";publicStr:" + publicStr + ";protectStr:" + protectStr + ";finalStr:" + finalStr ;          

     }

           

}

package com.hlmtest.java.reflect;

import java.lang.reflect.Field;

public class TestFieldObject {

      public static void main(String[] args ) {

            getFieldInfo ();

     }

     

      public static void getFieldInfo(){

            //先获取Class 对象实例

           Class<TestFieldClass> clzz = TestFieldClass. class ;

           Field[] DeclFieldList =  clzz .getDeclaredFields();

            for (Field field : DeclFieldList ){

                System. out .println( field .toString()+ ";" );

           }

           System. out .println( "<--我是华丽的分割线-->" );

           

           Field[] PublFieldList =  clzz .getFields();

            for (Field field : PublFieldList ){

                System. out .println( field .toString()+ ";" );

           }

           

     }

}

    运行结果为：

private java.lang.String com.hlmtest.java.reflect.TestFieldClass.privateStr;

public java.lang.String com.hlmtest.java.reflect.TestFieldClass.publicStr;

java.lang.String com.hlmtest.java.reflect.TestFieldClass.protectStr;

public static final java.lang.String com.hlmtest.java.reflect.TestFieldClass.finalStr;

<--我是华丽的分割线-->

public java.lang.String com.hlmtest.java.reflect.TestFieldClass.publicStr;

public static final java.lang.String com.hlmtest.java.reflect.TestFieldClass.finalStr;

取字段值

    根据字段名取得字段

package com.hlmtest.java.reflect;

import java.lang.reflect.Field;

public class TestFieldObject {

      public static void main(String[] args ) throws NoSuchFieldException, SecurityException {

            getFieldInfo ();

     }

     

      public static void getFieldInfo() throws NoSuchFieldException, SecurityException{

            //先获取Class 对象实例

           Class<TestFieldClass> clzz = TestFieldClass. class ;

           Field field =  clzz .getDeclaredField( "publicStr" );

           System. out .println( field .toString()+ ";" );

           

     }

     

}     

运行结果：

public java.lang.String com.hlmtest.java.reflect.TestFieldClass.publicStr;

通过Field 对象获取某实例的字段值： Object    get(Object obj)

import java.lang.reflect.InvocationTargetException;

public class TestFieldObject {

      public static void main(String[] args ) throws NoSuchFieldException, SecurityException, NoSuchMethodException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {

            getFieldInfo ();

     }

     

      public static void getFieldInfo() throws NoSuchFieldException, SecurityException, NoSuchMethodException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException{

            //先获取Class 对象实例

           Class<TestFieldClass> clzz = TestFieldClass. class ;

           

            //获取有参的构造方法对象

            @SuppressWarnings ( "rawtypes" )

           Class[] paramstr = {String. class ,String. class ,String. class };

           Constructor<TestFieldClass> instance = clzz .getConstructor( paramstr );

            //调用Constructor 的newInstance(Object... initargs ) 方法获得主对象实例

           TestFieldClass obj = instance .newInstance( "我是私有属性" , "我是公共属性" , "我是默认属性" );

           

           Field field =  clzz .getDeclaredField( "publicStr" );

           Object valueObj = field .get( obj );

           System. out .println( valueObj .toString()+ "" );

           

           Field[] fieldList =  clzz .getFields();

            for (Field f : fieldList ){

                Object value = f .get( obj );

                System. out .println( f .toString()+ "-->" + value .toString()+ ";" );

           }

     }

}

运行结果

我是公共属性

public java.lang.String com.hlmtest.java.reflect.TestFieldClass.publicStr-->我是公共属性;

public static final java.lang.String com.hlmtest.java.reflect.TestFieldClass.finalStr-->110;

要注意的是，这个方法只能获取公共字段的值，私有字段的值是无法获取 的，硬来要获取则会报：java.lang.IllegalAccessException

并且会告诉你 你这个Class  can not access a member of 某类 with modifiers "private"。道理很简单，私有的属性本来就是供人家自己用的，你不可能在外面直接操作人家的。

设置字段值

可以获取字段值自然就可以设置字段值，方法是：void    set(Object obj, Object value)

package com.hlmtest.java.reflect;

import java.lang.reflect.Constructor;

import java.lang.reflect.Field;

import java.lang.reflect.InvocationTargetException;

public class TestFieldObject {

      public static void main(String[] args ) throws NoSuchFieldException, SecurityException, NoSuchMethodException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {

            getFieldInfo ();

     }

     

      public static void getFieldInfo() throws NoSuchFieldException, SecurityException, NoSuchMethodException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException{

            //先获取Class 对象实例

           Class<TestFieldClass> clzz = TestFieldClass. class ;

           

            //获取有参的构造方法对象

            @SuppressWarnings ( "rawtypes" )

           Class[] paramstr = {String. class ,String. class ,String. class };

           Constructor<TestFieldClass> instance = clzz .getConstructor( paramstr );

            //调用Constructor 的newInstance(Object... initargs ) 方法获得主对象实例

           TestFieldClass obj = instance .newInstance( "我是私有属性" , "我是公共属性" , "我是默认属性" );

           

            //与取值一样，私有的字段也是不可以直接设值的，所以此处只取公共字段    

           Field[] fieldList =  clzz .getFields();

            for (Field f : fieldList ){

                 //final 修饰的字段是不可设值的，否则会报错，这里得排除

                 if ( f .toString().indexOf( "final" )>-1){

                      continue ;

                }

                 f .set( obj , f .getName()+ "我给你设值了哈" );

                Object value = f .get( obj );

                System. out .println( f .toString()+ "-->" + value .toString()+ ";" );

           }

     }

}

    运行结果：

public java.lang.String com.hlmtest.java.reflect.TestFieldClass.publicStr-->publicStr我给你设值了哈;

    到此也就差不多了，大家想要了解更多的使用方法的话当然还是文档啦。

Field 的更多API可以查询：

     中文网址：http://tool.oschina.net/apidocs/apidoc?api=jdk-zh

     英文网址：http://tool.oschina.net/apidocs/apidoc?api=jdk_7u4

其他

其他反射相关博客：

    JDK源码/*分析 ：反射包 java.lang.reflect② 之 Constructor 获取类的实例对象；

    JDK源码/*分析 ：反射包 java.lang.reflect ①之 Class 探秘；

    201800602