反射及利用反射复制对象的demo

落日映苍穹つ 2024-02-19 12:19 53阅读 0赞

反射是java编程的灵魂，在用反射之前有几个类需要了解：Class，Method，Feild，Constructor，在demo中演示这些类中比较常用的方法，然后用反射实现copy对象的封装类来说明反射的微妙。

1、常用方法：

public class ReflectDemo {
    
        /** Class */
        @Test
        public void testClass() throws Exception{
            Class<?> claz = People.class;
            // 1、getMethods(), 获取所有方法，包括notify等从Object继承的方法
            Method[] methods = claz.getMethods();
            Arrays.asList(methods).forEach(method -> System.out.println(method.getName()));
    
            // 2、getMethod(String name, Class<?>... parameterTypes), 方法名及参数列表
            Method method = claz.getMethod("setName", String.class);
            System.out.println(method.getName());
    
            // 3、getClassLoader(), 加载器
            System.out.println(claz.getClassLoader());
    
            // 4、newInstance(), 获取实例
            Object instance = claz.newInstance();
            if (instance instanceof People) {
                People people = (People) instance;
                people.setAddress("广东深圳");
                System.out.println(people);
            }
    
            System.out.println("------------Field-------------");
            // 5、getFields(), 获取共有属性字段
            Field[] fields = claz.getFields();
            Arrays.asList(fields).stream().forEach(field -> System.out.println(field.getName()));
    
            // 6、getDeclaredFields(), 获取所有字段，包括私有
            Field[] declaredFields = claz.getDeclaredFields();
            Arrays.asList(declaredFields).stream().forEach(field -> System.out.println(field.getName()));
    
            System.out.println("------------Constructor-------------");
            // 7、getConstructors(), 获取构造方法
            Constructor<?>[] constructors = claz.getConstructors();
            Arrays.asList(constructors).stream().forEach(constructor -> System.out.println(constructor.getParameterCount()));
        }
    
        /** Method */
        @Test
        public void testMethod() throws Exception{
            People people = new People("11001", "张三", "广东深圳", "程序员");
            Class<?> clazz = people.getClass();
            Constructor<?> constructor = clazz.getConstructor(String.class, String.class, String.class, String.class);
            System.out.println(constructor.getName());
    
            Method action = clazz.getMethod("action", String.class, String.class, String.class);
    
            // 1、getName(), 方法名称
            String name = action.getName();
            System.out.println(name);
    
            // 2、getParameterCount(), 参数数量
            int parameterCount = action.getParameterCount();
            System.out.println(parameterCount);
    
            // 3、getParameterTypes(), 参数类型
            Class<?>[] parameterTypes = action.getParameterTypes();
            Arrays.asList(parameterTypes).stream().forEach(para -> System.out.println(para.getName()));
    
            // 4、getReturnType(), 获取返回类型
            Class<?> returnType = action.getReturnType();
            System.out.println(returnType.getName());
    
            // 5、getDeclaredAnnotations(), 获取使用的注解
            Annotation[] declaredAnnotations = action.getDeclaredAnnotations();
            System.out.println(declaredAnnotations.length);
    
            // 6、改变对象的值
            Method setAddress = clazz.getMethod("setAddress", String.class);
            setAddress.invoke(people, "北京市海淀区");
            System.out.println(people);
    
            System.out.println("***** and so on *****");
        }
    
        /** Field */
        @Test
        public void testField() throws Exception{
            People people = new People("11001", "张三", "广东深圳", "程序员");
            Class<?> clazz = people.getClass();
    
            // 1、getField(), 只能获取共有字段
            Field field = clazz.getField("work");
            Object work = field.get(people);
            System.out.println(work);
    
            // 2、getDeclaredField(), 可以获取包括私有字段
            Field address = clazz.getDeclaredField("address");
            // 设置访问权限
            address.setAccessible(true);
            Object o = address.get(people);
            System.out.println(o);  // out -> 广东深圳
        }
    }

2、很多情况下，在java编程中可能会遇到VO,DO对象相互转换的情况，同时两个实体类的字段比较相似，当然可以通过写setter方法来手动设置（试想有几十个字段的时候呢），这里通过反射实现一个封装，简化冗余的set赋值:

public class CopyDemo {
    
        @Test
        public void testCopy() throws Exception{
            StudentDO studentDO = new StudentDO(1101, "张三", "2015018", 98.5, "man", "football", 25);
            StudentVO studentVO = new StudentVO();
    
            // studentDO -> studentVO
            copyUtils(studentDO, studentVO);
    
            System.out.println(studentVO);
        }
    
        private void copyUtils( StudentDO studentDO, StudentVO studentVO) throws Exception{
            Class<?> clazzVO = studentVO.getClass();
            Class<?> clazzDO = studentDO.getClass();
    
            Method[] methodsVO = clazzVO.getMethods();
            for (Method methodVO : methodsVO) {
                // VO的set方法
                String nameVO = methodVO.getName();
                if (!nameVO.startsWith("set")) {
                    continue;
                }
                // 获取VO参数类型
                Class<?>[] parameterTypes = methodVO.getParameterTypes();
                if (parameterTypes.length < 1) {
                    continue;
                }
                Class<?> paraType = parameterTypes[0];
    
                // DO的get方法
                String nameDO = "get" + StringUtils.toUpperCase(nameVO.charAt(3) + "") + nameVO.substring(4);
                Method methodDO = clazzDO.getMethod(nameDO);
                // 获取DO返回类型
                Class<?> returnType = methodDO.getReturnType();
                // 通过get获取值
                Object invokeValue = methodDO.invoke(studentDO);
    
                // 按理说returnType和paraType类型一致, 如果不一致判断后转换即可
                if (returnType.getName().equals(paraType.getName())) {
                    methodVO.invoke(studentVO, invokeValue);
                }
            }
        }
    }

两个实体类（除了雷名不同，其他先设定为相同）

StudentVO.java:

public class StudentVO {
        private Integer id;
        private String name;
        private String sno;
        private Double score;
        private String sex;
        private String hobby;
        private Integer age;
    
        public StudentVO() {
    
        }
        public StudentVO(Integer id, String name, String sno, Double score, String sex, String hobby, Integer age) {
            this.id = id;
            this.name = name;
            this.sno = sno;
            this.score = score;
            this.sex = sex;
            this.hobby = hobby;
            this.age = age;
        }
    
        public Integer getId() {
            return id;
        }
    
        public void setId(Integer id) {
            this.id = id;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public String getSno() {
            return sno;
        }
    
        public void setSno(String sno) {
            this.sno = sno;
        }
    
        public Double getScore() {
            return score;
        }
    
        public void setScore(Double score) {
            this.score = score;
        }
    
        public String getSex() {
            return sex;
        }
    
        public void setSex(String sex) {
            this.sex = sex;
        }
    
        public String getHobby() {
            return hobby;
        }
    
        public void setHobby(String hobby) {
            this.hobby = hobby;
        }
    
        public Integer getAge() {
            return age;
        }
    
        public void setAge(Integer age) {
            this.age = age;
        }
    
        @Override
        public String toString() {
            return "StudentVO{" +
                    "id=" + id +
                    ", name='" + name + '\'' +
                    ", sno='" + sno + '\'' +
                    ", score=" + score +
                    ", sex='" + sex + '\'' +
                    ", hobby='" + hobby + '\'' +
                    ", age=" + age +
                    '}';
        }
    }

StudentDO.java

public class StudentDO {
        private Integer id;
        private String name;
        private String sno;
        private Double score;
        private String sex;
        private String hobby;
        private Integer age;
    
        public StudentDO() {
    
        }
        public StudentDO(Integer id, String name, String sno, Double score, String sex, String hobby, Integer age) {
            this.id = id;
            this.name = name;
            this.sno = sno;
            this.score = score;
            this.sex = sex;
            this.hobby = hobby;
            this.age = age;
        }
    
        public Integer getId() {
            return id;
        }
    
        public void setId(Integer id) {
            this.id = id;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public String getSno() {
            return sno;
        }
    
        public void setSno(String sno) {
            this.sno = sno;
        }
    
        public Double getScore() {
            return score;
        }
    
        public void setScore(Double score) {
            this.score = score;
        }
    
        public String getSex() {
            return sex;
        }
    
        public void setSex(String sex) {
            this.sex = sex;
        }
    
        public String getHobby() {
            return hobby;
        }
    
        public void setHobby(String hobby) {
            this.hobby = hobby;
        }
    
        public Integer getAge() {
            return age;
        }
    
        public void setAge(Integer age) {
            this.age = age;
        }
    
        @Override
        public String toString() {
            return "StudentDO{" +
                    "id=" + id +
                    ", name='" + name + '\'' +
                    ", sno='" + sno + '\'' +
                    ", score=" + score +
                    ", sex='" + sex + '\'' +
                    ", hobby='" + hobby + '\'' +
                    ", age=" + age +
                    '}';
        }
    }