学习Java的反射机制和Annotation

1、创建一个Annotation类JavaAnnotation.java。

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface JavaAnnotation {
    String value();
}

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface JavaAnnotation {
	String value(); 
}

2、创建测试类。

import java.lang.reflect.Field;
import java.lang.reflect.Method;

/**
 * 学习java的反射机制
 *
 * @author sunny
 *
 */
public class ReflectTest {

    @JavaAnnotation("字段注释")
    public String field1;

    private String filed2;

    public String getFiled2() {
        return filed2;
    }

    public void setFiled2(String filed2) {
        this.filed2 = filed2;
    }

    public String getField1() {
        return field1;
    }

    public void setField1(String field1) {
        this.field1 = field1;
    }

    private void act() {
        System.out.println("do nothing here......");
    }

    public static void main(String[] args) {
        try {
            Class a = Class.forName("ReflectTest");

            // 列举该类的所有字段
            Field[] fileds = a.getDeclaredFields();
            for (int i = 0; i < fileds.length; i++) {
                System.out.println(i + " - " + fileds[i].toString());
            }
            System.out.println("////////////////////字段列举完毕");

            // 列举该类的所有方法
            Method[] methods = a.getDeclaredMethods();
            for (int i = 0; i < methods.length; i++) {
                System.out.println(i + " - " + methods[i].toString());
            }
            System.out.println("////////////////////方法列举完毕");

            // 调用类方法
            try {
                // 通过默认构造方法创建一个新的实例对象
                Object instance = a.getConstructor(new Class[] {}).newInstance(
                        new Object[] {});
                Method m = a.getDeclaredMethod("act");
                m.invoke(instance, new Object[] {});
                System.out.println("////////////////////方法调用完毕");

            } catch (Exception e) {
                e.printStackTrace();
            }

            // 操作Annotation
            try {
                Field f = a.getDeclaredField("field1");
                if (f.isAnnotationPresent(JavaAnnotation.class))
                    System.out.println("JavaAnnotation of field1 is '"
                            + f.getAnnotation(JavaAnnotation.class).value()
                            + "'");

            } catch (Exception e) {
                e.printStackTrace();
            }
        } catch (ClassNotFoundException e2) {
            e2.printStackTrace();
        }
    }
}