自定义annotation 实现注入功能（笔记,以备后查）

1.Annotation  class

package com.test;

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

@Retention(RetentionPolicy.RUNTIME)
@Target( { ElementType.FIELD,ElementType.METHOD })//允许在method 和 field 使用annotation
public @interface ServiceInject {
   Class name();
}

2. service 接口，及2个实现方法

package com.test;

public interface ITestService {
        public String save();
}

package com.test;

public class TestService_1 implements ITestService {

	public String save() {
		return this.getClass().getSimpleName() +" class was invoked";
	}

}

package com.test;

public class TestService_2 implements ITestService {

	public String save() {
		return this.getClass().getSimpleName()+" class was invoked";
	}

}

3. 模拟的拦截器

package com.test;

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

public class SimilarToTheInterceptor {
	public static void scanAllFieldsAndMethods(Object obj) {
		Field[] fields = obj.getClass().getDeclaredFields();// 获取所有类型的field
		Method[] methods = obj.getClass().getMethods(); // 方法一般是public 
		for (Field f : fields) {
			if (f.isAnnotationPresent(ServiceInject.class)) {
				ServiceInject ie = f.getAnnotation(ServiceInject.class);
				Class name = ie.name();
				boolean flag = f.isAccessible();//保存当前field的修饰类型
				try {
					f.setAccessible(true);//强制field 可以访问
					f.set(obj, f.getType().cast(name.newInstance()));//使用cast 强制转换类型
					f.setAccessible(flag);//还原当前field 的修饰类型，避免被不非法使用
				} catch (IllegalArgumentException e) {
					e.printStackTrace();
				} catch (IllegalAccessException e) {
					e.printStackTrace();
				} catch (InstantiationException e1) {
					e1.printStackTrace();
				}

			}
		}
		for (Method m : methods) {//set注入
			if (m.isAnnotationPresent(ServiceInject.class) && m.getName().indexOf("set")!=-1)  {
				ServiceInject ie = m.getAnnotation(ServiceInject.class);
				Class name = ie.name();
				try {
					m.setAccessible(true);
					m.invoke(obj, name.newInstance());
				} catch (IllegalArgumentException e) {
					e.printStackTrace();
				} catch (IllegalAccessException e) {
					e.printStackTrace();
				} catch (InstantiationException e1) {
					e1.printStackTrace();
				} catch (InvocationTargetException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}

			}
		}
	}

}

4.模拟的Action

package com.test;


@SuppressWarnings("unused")
public class TestAction {
	@ServiceInject(name = TestService_1.class)
	public ITestService testService1;
	
	private ITestService testService2;
   

	public void saveDate1() {
		System.out.println("==========Saved======"+testService1.save());
	}
	public void saveDate2() {
		System.out.println("==========Saved======"+testService2.save());
	}


	@ServiceInject(name = TestService_2.class)
	public void setTestService2(ITestService testService2) {
		this.testService2 = testService2;
	}
	
}

5. 测试类

package com.test;

public class Main {
	public static void main(String[] args) {
          TestAction  action = new TestAction();
          SimilarToTheInterceptor.scanAllFieldsAndMethods(action);// 模拟拦截器功能
          action.saveDate1();
          action.saveDate2();
	}
}

6. 结果：
==========Saved======TestService_1 class was invoked
==========Saved======TestService_2 class was invoked