反射机制（java）

反射机制

反射机制可通过在运行时加载类名而获取类，并对其进行操作。工厂模式，动态代理中较常用到。

在实际场景中：由于有好多类具有共同的接口样式，而他们又用的不是很频繁，如果在服务器中保有这些类会占用资源空间，如果通过接口指定的方式去加载，用完之后就销毁掉，可节省资源空间，且实现接口编程，扩展性好，代码量也少。打个比方：哺乳动物Animal为接口，里面包括获取乳头数，获取腿，获取头，获取尾巴等，像这种都具有一定共性，实现类为老虎，狮子，兔子，羊等等等。

1.获取className,常用的形式将需要反射的类放在属性文件*.properties或数据库字段中，通过key获取类名及路径。

 private static final String CLASS_NAME_PATH = "pattern/classname.properties";

     /**
      * 获取类名称
      * @return
      */
     private static String getClassName(String name) {
         Properties pro = new Properties();
         try {
             String url = ProxyFactory.class.getClassLoader().getResource("").getPath() + CLASS_NAME_PATH;
             pro.load(new FileInputStream(url));
         } catch (FileNotFoundException e) {
             e.printStackTrace();
         } catch (IOException e) {
             e.printStackTrace();
         }
         return (String)pro.get(name);
     }

getClassName

 # animal
 lion = pattern.creation.factory.animal.Lion
 sheep = pattern.creation.factory.animal.Sheep
 rabit = pattern.creation.factory.animal.Rabit
 # plant
 apple = pattern.creation.factory.plant.Apple
 pear = pattern.creation.factory.plant.Pear
 plum = pattern.creation.factory.plant.Plum

classPath.properties

>>> String strClass = getClassName("rabit");//获取兔子类

2.获取类，创建类实例

Class<?> clazz = Class.forName(strClass);  //获取类

Object obj = clazz.newInstance()；            //构建实例对象

Class<?> superClazz = clazz.getSuperclass(); //获取父类
Class<?>[] interfaceArray = clazz.getInterfaces();//获取接口

     /**
      * 根据classname获取类名
      * @param strName
      * @return
      * @throws ClassNotFoundException
      * @throws InstantiationException
      * @throws IllegalAccessException
      */
     @SuppressWarnings("unchecked")
     public <T> T getClassByName(String strName) throws ClassNotFoundException, InstantiationException, IllegalAccessException {
         String strClass = getClassName(strName);
         Class<?> clazz = Class.forName(strClass);
         Class<?> superClazz = clazz.getSuperclass();
         Class<?>[] interfaceArray = clazz.getInterfaces();
         System.out.println("className--: " + clazz.getName());//当前类名
         System.out.println("superClassName--: " + superClazz.getName());//父类
         for(Class<?> interfaces: interfaceArray){
             System.out.println("interface--: " + interfaces.getName());//接口
         }
         return (T)clazz.newInstance();
     }

getClass

>>> AnimalFactory animal = reflectFactory.getClassByName("rabit");

运行结果：

className--: pattern.creation.factory.animal.Rabit
superClassName--: pattern.creation.factory.animal.Animals
interface--: pattern.creation.factory.animal.AnimalFactory

3. 获取类属性及信息

Field[] fieldArray = clazz.getDeclaredFields(); // 显示所有的属性
Field[] publicFieldArray = clazz.getFields(); //显示public属性的元素

String name = field.getName();    //获取方法名

String modify = Modifier.toString(field.getModifiers());   // 修饰词
String classType = field.getType().getSimpleName();    // 类型
Annotation[] annoArray = field.getAnnotations();        // 注解

field.setAccessible(true);        //获取value要赋予权限

Object obj = clazz.newInstance();    //对象实例
Object value = field.get(obj);// 私有属性需要获取权限才可以

field.set(obj, value + "-----changed..");// 修改私有属性的值

     /**
      * 通过反射机制获取类 的属性名及其内容
      * @param strName
      * @throws ClassNotFoundException
      * @throws InstantiationException
      * @throws IllegalAccessException
      */
     public void getClassFieldByName(String strName) throws ClassNotFoundException, InstantiationException, IllegalAccessException {
         String strClass = getClassName(strName);
         Class<?> clazz = Class.forName(strClass);
         Object obj = clazz.newInstance();
         Field[] fieldArray = clazz.getDeclaredFields(); // 显示所有的属性
         Field[] publicFieldArray = clazz.getFields();  //显示public属性的元素
         Field[] newFieldArray = (Field[])ArrayUtils.addAll(fieldArray, publicFieldArray);
         for(Field field : newFieldArray){
             String name = field.getName();
             String modify = Modifier.toString(field.getModifiers());
             String classType = field.getType().getSimpleName();
             Annotation[] annoArray = field.getAnnotations();
             String strAnno = "";
             for(Annotation anno : annoArray){
                 strAnno += "@"+anno.annotationType().getSimpleName();
             }
             field.setAccessible(true);
             Object value = field.get(obj);// 私有属性需要获取权限才可以
             System.out.println("propertyName:  " + strAnno + "  " + modify+ " " + classType + " " + name + "=" + value);
             if(!StringUtils.contains(modify, "final")){
                 field.set(obj, value + "-----changed..");// 修改私有属性的值
                 System.out.println("propertyName:  " + strAnno + "  " + modify+ " " + classType + " " + name + "=" + value);
             }
         }

         Field[] fieldsArray = clazz.getSuperclass().getDeclaredFields();//父类的属性名
         for(Field field : fieldsArray){
             String name = field.getName();
             String modify = Modifier.toString(field.getModifiers());
             String classType = field.getType().getSimpleName();
             field.setAccessible(true);
             Object value = field.get(obj);// 私有属性需要获取权限才可以
             System.out.println("superPropertyName: " + modify+ " " + classType + " " + name + "=" + value);
         }
     }

getClassFieldByName

>>> reflectFactory.getClassFieldByName("rabit");

运行结果:

propertyName: private String rabitName=I am rabit
propertyName: private String rabitName=I am rabit
propertyName: private String header=
propertyName: private String header=
propertyName: private static final int LEGS=4
propertyName: @Resource public String tails=1tails
propertyName: @Resource public String tails=1tails
propertyName: @Resource public String tails=1tails-----changed..
propertyName: @Resource public String tails=1tails-----changed..
superPropertyName: private static final long serialVersionUID=8482086762730882629
superPropertyName: private int slegs=0
superPropertyName: private int shands=0
superPropertyName: private int sheader=0

4. 获取方法，及方法调用

String modifier = Modifier.toString(method.getModifiers()); //修饰词
String returnType = method.getReturnType().getSimpleName();//返回类型
String name = method.getName();//方法名
Parameter[] parameters = method.getParameters();//参数列表
Annotation[] annoArray = method.getAnnotations();//注解列表

Method method = clazz.getMethod(methodName, classes); //根据方法名，获取方法

method.invoke(obj, orgs)； //方法调用  注意invoke的第一个参数为方法对应的类的实例。

UserDTO dto = new UserDTO();
dto.setId("");
System.out.println(dto.getClass().getMethod("getId").invoke(dto));

     /**
      * 获取方法并调用方法
      * @param strName
      * @param methodName
      * @param orgs
      * @param classes
      * @throws ClassNotFoundException
      * @throws InstantiationException
      * @throws IllegalAccessException
      * @throws NoSuchMethodException
      * @throws SecurityException
      * @throws IllegalArgumentException
      * @throws InvocationTargetException
      */
     public void getRunMethodByMethodName(String strName, String methodName, Object[] orgs, Class<?>[] classes) throws ClassNotFoundException, InstantiationException, IllegalAccessException, NoSuchMethodException, SecurityException, IllegalArgumentException, InvocationTargetException {
         String strClass = getClassName(strName);
         Class<?> clazz = Class.forName(strClass);
         Class<?> superClazz = clazz.getSuperclass();
         Object obj = clazz.newInstance();
         Method[] methodArray = clazz.getDeclaredMethods();
         Method[] supeMethodArray = superClazz.getDeclaredMethods();
         Method[] sumMethodArray = (Method[])ArrayUtils.addAll(methodArray, supeMethodArray);
         for(Method method : sumMethodArray){
             String modifier = Modifier.toString(method.getModifiers());
             String returnType = method.getReturnType().getSimpleName();
             String name = method.getName();
             Parameter[] parameters = method.getParameters();
             Annotation[] annoArray = method.getAnnotations();
             String strAnno = "";
             for(Annotation anno : annoArray){
                 strAnno += "@"+anno.annotationType().getSimpleName();
             }
             String strPara = "";
             for(Parameter para : parameters){
                 strPara+=para.getType().getSimpleName() + "  " + para.getName() + ",";
             }
             System.out.println("method:----"+strAnno + "  " + modifier + " " + returnType + " " + name + "(" + strPara +")");
         }
         Method method = clazz.getMethod(methodName, classes);
         System.out.println("header:  " + method.invoke(obj, orgs));
     }

getRunMethodByMethodName

>>> Class<?>[] classArray = {String.class,int.class,String.class};
>>> Object[] paramsArray = {"兔子只有",1,"头"};
>>> reflectFactory.getRunMethodByMethodName("rabit", "getHeader",paramsArray, classArray);

运行结果：

method:---- public String getHeader()
method:---- public String getHeader(String arg0,int arg1,String arg2,)
method:---- public int getLegs()
method:---- public int getLegs()

header:  兔子只有$$$$1@@@@@@头

5. 构造体方法

clazz.getConstructors()  // 获取所有的构造体

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以上，为个人总结，如有写的不当之处，还望指正。

-----------DennyZhao