getDeclaredFields()应用

淩亂°似流年 2022-08-21 13:44 77阅读 0赞

## **调用private类型的变量及方法** ##

BeanUtils.java

package com.lmb.util;
    
    import org.apache.commons.lang.StringUtils;
    import org.apache.commons.logging.Log;
    import org.apache.commons.logging.LogFactory;
    import org.springframework.util.Assert;
    import org.springframework.util.ReflectionUtils;
    
    import java.lang.reflect.Field;
    import java.lang.reflect.Method;
    import java.util.ArrayList;
    import java.util.List;
    
    /**
     * 扩展Apache Commons BeanUtils, 提供一些反射方面缺失功能的封装.
     */
    public class BeanUtils extends org.apache.commons.beanutils.BeanUtils {
        
    
        protected static final Log logger = LogFactory.getLog(BeanUtils.class);
    
        private BeanUtils() {
        }
    
        /**
         * 循环向上转型,获取对象的DeclaredField.
         *
         * @throws NoSuchFieldException 如果没有该Field时抛出.
         */
        public static Field getDeclaredField(Object object, String propertyName) throws NoSuchFieldException {
            Assert.notNull(object);
            Assert.hasText(propertyName);
            return getDeclaredField(object.getClass(), propertyName);
        }
    
        /**
         * 循环向上转型,获取对象的DeclaredField.
         *
         * @throws NoSuchFieldException 如果没有该Field时抛出.
         */
        public static Field getDeclaredField(Class clazz, String propertyName) throws NoSuchFieldException {
            Assert.notNull(clazz);
            Assert.hasText(propertyName);
            for (Class superClass = clazz; superClass != Object.class; superClass = superClass.getSuperclass()) {
                try {
                    return superClass.getDeclaredField(propertyName);
                } catch (NoSuchFieldException e) {
                    // Field不在当前类定义,继续向上转型 
                }
            }
            throw new NoSuchFieldException("No such field: " + clazz.getName() + '.' + propertyName);
        }
    
        /**
         * 暴力获取对象变量值,忽略private,protected修饰符的限制.
         *
         * @throws NoSuchFieldException 如果没有该Field时抛出.
         */
        public static Object forceGetProperty(Object object, String propertyName) throws NoSuchFieldException {
            Assert.notNull(object);
            Assert.hasText(propertyName);
    
            Field field = getDeclaredField(object, propertyName);
    
            boolean accessible = field.isAccessible();
            field.setAccessible(true);
    
            Object result = null;
            try {
                result = field.get(object);
            } catch (IllegalAccessException e) {
                logger.info("error wont' happen");
            }
            field.setAccessible(accessible);
            return result;
        }
    
        /**
         * 暴力设置对象变量值,忽略private,protected修饰符的限制.
         *
         * @throws NoSuchFieldException 如果没有该Field时抛出.
         */
        public static void forceSetProperty(Object object, String propertyName, Object newValue)
                throws NoSuchFieldException {
            Assert.notNull(object);
            Assert.hasText(propertyName);
    
            Field field = getDeclaredField(object, propertyName);
            boolean accessible = field.isAccessible();
            field.setAccessible(true);
            try {
                field.set(object, newValue);
            } catch (IllegalAccessException e) {
                logger.info("Error won't happen");
            }
            field.setAccessible(accessible);
        }
    
        /**
         * 暴力调用对象函数,忽略private,protected修饰符的限制.
         *
         * @throws NoSuchMethodException 如果没有该Method时抛出.
         */
        @SuppressWarnings("unchecked")
        public static Object invokePrivateMethod(Object object, String methodName, Object... params)
                throws NoSuchMethodException {
            Assert.notNull(object);//object对象不为空，否则抛出异常
            Assert.hasText(methodName);//methodName 不能为 null 且必须至少包含一个非空格的字符，否则抛出异常
            Class[] types = new Class[params.length];
            for (int i = 0; i < params.length; i++) {
                types[i] = params[i].getClass();
            }
    
            Class clazz = object.getClass();
            Method method = null;
            for (Class superClass = clazz; superClass != Object.class; superClass = superClass.getSuperclass()) {
                try {
                    //获取superClass类自身声明的符合入参要求的所有方法，包含public、protected和private方法
                    method = superClass.getDeclaredMethod(methodName, types);
                    break;
                } catch (NoSuchMethodException e) {
                    // 方法不在当前类定义,继续向上转型
                }
            }
    
            if (method == null)
                throw new NoSuchMethodException("No Such Method:" + clazz.getSimpleName() + methodName);
    
            boolean accessible = method.isAccessible();//获取方法的可用性情况
            method.setAccessible(true);
            Object result = null;
            try {
                result = method.invoke(object, params);//调用该方法
            } catch (Exception e) {
                ReflectionUtils.handleReflectionException(e);
            }
            method.setAccessible(accessible);//还原方法的可用性情况
            return result;
        }
    
        /**
         * 按Filed的类型取得Field列表.
         */
        public static List<Field> getFieldsByType(Object object, Class type) {
            List<Field> list = new ArrayList<Field>();
            Field[] fields = object.getClass().getDeclaredFields();
            for (Field field : fields) {
                if (field.getType().isAssignableFrom(type)) {
                    list.add(field);
                }
            }
            return list;
        }
    
        /**
         * 按FiledName获得Field的类型.
         */
        public static Class getPropertyType(Class type, String name) throws NoSuchFieldException {
            return getDeclaredField(type, name).getType();
        }
    
        /**
         * 获得field的getter函数名称.
         */
        public static String getGetterName(Class type, String fieldName) {
            Assert.notNull(type, "Type required");
            Assert.hasText(fieldName, "FieldName required");
    
            if (type.getName().equals("boolean")) {
                return "is" + StringUtils.capitalize(fieldName);
            } else {
                return "get" + StringUtils.capitalize(fieldName);
            }
        }
    
        /**
         * 获得field的getter函数,如果找不到该方法,返回null.
         */
        public static Method getGetterMethod(Class type, String fieldName) {
            try {
                return type.getMethod(getGetterName(type, fieldName));
            } catch (NoSuchMethodException e) {
                logger.error(e.getMessage(), e);
            }
            return null;
        }
    }

## **实现java反射调用别的类** ##

### 写一个类Simple.java ###

public class Simple {
     private void displayMessage(String strMsg) {
      System.out.println("message is:" + strMsg);
     }
    }

### 反射调用 ###

import java.lang.reflect.*;
    
    public class Test {
        
    
     /**
      * @param args
      * @throws ClassNotFoundException
      * @throws NoSuchMethodException
      * @throws SecurityException
      * @throws IllegalAccessException
      * @throws InstantiationException
      * @throws InvocationTargetException
      * @throws IllegalArgumentException
      */
     public static void main(String[] args) throws ClassNotFoundException,
       SecurityException, NoSuchMethodException, InstantiationException,
       IllegalAccessException, IllegalArgumentException,
       InvocationTargetException {
    
      Class simpleClass = Class.forName("Simple");
      Object simpelObject = simpleClass.newInstance();//获取simple类的实例对象
      Class[] args1 = new Class[1];
      args1[0] = String.class;
    
      Method simpleMethod = simpleClass.getDeclaredMethod("displayMessage",
        args1);
    //得到方法名为displayMessage，参数类型为args1内的参数类型的方法（private 
    
    public protected）
    
      simpleMethod.setAccessible(true);//设置方法可用
    
      String[] argments = new String[1];
      argments[0] = "Hello,world";
      simpleMethod.invoke(simpelObject, argments);//调用该方法
    
     }
    }