java 注解 - 爱码网

注解基本信息

自定义注解及使用

定义注解

package com.hsh.annotation;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 *  定义注解 @ServiceAno
 *  保留到运行时，作用对象为方法
 */
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface ServiceAno {
	 String service();
}

解析注解

package com.hsh.annotation;

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

public class ServiceAnoParser {
	
	/*
	 * 解析注解，完成service的注入
	 */
	public static void setService(Object action) throws SecurityException, 
	NoSuchMethodException, ClassNotFoundException, IllegalArgumentException, 
	IllegalAccessException, InvocationTargetException, InstantiationException{
		
		Class<Action> clazz = (Class<Action>) action.getClass();
		for(Field f : clazz.getDeclaredFields()){
			for(Annotation ann : f.getDeclaredAnnotations()){
				if(ann instanceof ServiceAno){
					String methodName = getSetter(f.getName());
					Method setter = clazz.getMethod(methodName, Service.class);
					setter.setAccessible(true);
					ServiceAno sa = (ServiceAno)ann;
					String service = sa.service();
					Class serClazz = Class.forName(service);
					setter.invoke(action, serClazz.newInstance());
				}
			}
		}
	}
	
	/**
	 * 生成set方法的方法名字符串 
	 */
	public static String getSetter(String fieldName){
		String name = "set";
		name += (fieldName.charAt(0) + "").toUpperCase();
		if(fieldName.length() > 1 ){
			name += fieldName.substring(1);
		}
		return name;
	}
}

使用注解

package com.hsh.annotation;

public interface Service {
	public void service();
}

package com.hsh.annotation;

public class OracleService implements Service{
	@Override
	public void service(){
		System.out.println("oracle service...");
	}
}

package com.hsh.annotation;

public class MySqlService implements Service{
	
	@Override
	public void service(){
		System.out.println("mysql service...");
	}
}

package com.hsh.annotation;

public class Action {
	
	//使用@ServiceAno 将MySqlService实例注入给mySqlService
	@ServiceAno(service = "com.hsh.annotation.MySqlService")
	private Service mySqlService;
	
	//使用@ServiceAno 将OracleService实例注入给oracleService
	@ServiceAno(service = "com.hsh.annotation.OracleService")
	private Service oracleService;
	
	public void service(){
		mySqlService.service();
		oracleService.service();
	}

	public Service getMySqlService() {
		return mySqlService;
	}

	public void setMySqlService(Service mySqlService) {
		this.mySqlService = mySqlService;
	}

	public Service getOracleService() {
		return oracleService;
	}

	public void setOracleService(Service oracleService) {
		this.oracleService = oracleService;
	}
}

测试

package com.hsh.annotation;

public class Main {
	public static void main(String[] args) {
		Action action = new Action();
		try {
			ServiceAnoParser.setService(action);
			action.service();
		}catch (Exception e) {
			e.printStackTrace();
		}
	}
}

测试结果

java 注解