手写spring ioc注解方式(包扫描)+注解

项目结构 注解创建方式
注解创建方式

使用注解可以避免在包扫描的时候为接口创建对象报错的问题

package annotation;

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

/**
 *注解是java中的一种元数据-描述Java对象
 *用于描述java对象
 *本质上也是一个类(字节码对象)
 *它是jdk1.5的特性(jdk1.5就有了)
 *@Retention 表示定义的注解何时有效,RUNTIME运行时有效
 *@Target 表示定义的注解运行在哪里,TYPE应用在类上,METHOD应用在方法上,FIELD应用在类上
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface Component {

}

package annotation;

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

/**
 *{ElementType.TYPE}的花括号可以省略，如:ElementType.TYPE,因为只有一个值
 *{ElementType.TYPE,ElementType.METHOD,ElementType.FIELD}
 */
@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.TYPE })
public @interface Controller {

}

package annotation;

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.TYPE})
public @interface Service {

}

package factory;

import java.io.File;
import java.io.FileFilter;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;

import annotation.Component;
import annotation.Controller;
import annotation.Service;

public class AnnotationApplicationContext {
    private Map<String,Object> beanMap=new HashMap<>();
    public AnnotationApplicationContext() {
        String pkg="project";
        scanPackage(pkg);
        
    }
    private void scanPackage(final String pkg){
        String pkgDir=pkg.replaceAll("\\.", "/");
        URL url = getClass().getClassLoader().getResource(pkgDir);
        File file=new File(url.getFile());
        File fs[]=file.listFiles(new FileFilter() {
            
            @Override
            public boolean accept(File file) {
                String fName=file.getName();
                if(file.isDirectory()){
                    scanPackage(pkg+"."+fName);
                }else{
                    //判断文件后缀是否为.
                    if(fName.endsWith(".class")){
                        return true;
                    }
                }
                return false;
            }
        });
        for (File f : fs) {
            String fName=f.getName();
            //去除.class以后的文件名
            fName=fName.substring(0,fName.lastIndexOf("."));
            //将名字的第一个字母转为小写(用它作为key存储map)
            String key=String.valueOf(fName.charAt(0)).toLowerCase()+fName.substring(1);
            //构建一个类全名(包名.类名)
            String pkgCls=pkg+"."+fName;
            try {
                //反射构建对象
                Class<?> c = Class.forName(pkgCls);
                //判定类上是否有注解isAnnotationPresent()
                if(c.isAnnotationPresent(Controller.class)||
                        c.isAnnotationPresent(Service.class)||
                        c.isAnnotationPresent(Component.class)
                        ){
                    Object obj = c.newInstance();
                    //将对象放到map容器
                    beanMap.put(key, obj);
                }
                
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }
    }
    public Object getBean(String key){
        return beanMap.get(key);
    }
    public void close(){
        beanMap.clear();
        beanMap=null;
    }
}

package project.controller;

import annotation.Controller;

@Controller
public class CarController {
    public void show(){
        System.out.println("CarController");
    }
}

package project.service.impl;

import annotation.Service;
import project.service.CarSercice;

@Service
public class CarServiceImpl implements CarSercice {
    public void save(){
        System.out.println("save car...");
    }
}

package project.service;

public interface CarSercice {
    void save();
}

package test;

import factory.AnnotationApplicationContext;
import project.controller.CarController;
import project.service.impl.CarServiceImpl;

public class TestApp {
    public static void main(String[] args) {
        AnnotationApplicationContext ctx=new AnnotationApplicationContext();
        CarController obj = (CarController) ctx.getBean("carController");
        System.out.println(obj);
        obj.show();
        
        CarServiceImpl obj2=(CarServiceImpl) ctx.getBean("carServiceImpl");
        System.out.println(obj2);
        obj2.save();
        ctx.close();
        
    }
}

运行TestApp的运行结果

project.controller.CarController@5323cf50
CarController
project.service.impl.CarServiceImpl@53ffb7d4
save car...