Spring中的Bean

Bean的配置元素：name=id,class ,contructor-arg,ref,scope,value,list,set,map,entry,property
Bean的scope：singleton(默认值，重点),prototype(重点),request,session,application,websocket
Bean的装配方式：基于xml配置文件的装配，基于annotation的装配，基于自动加载的装配方式

注意：如果在Bean中未指定id和name，那么spring会把class值当作id

基于xml配置文件的装配

设值注入,xml的配置内容如下

注意：在bean文件中需要对属性添加set方法,且一定要有一个无参的构造方法

package com.xyj.demo;
import java.util.List;

public class SetBean {

    private String username;
    private int age;
    private String password;
    private List listHouse;
    public SetBean(){
        super();
    }
    public void setAge(int age) {
        this.age = age;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public void setListHouse(List listHouse) {
        this.listHouse = listHouse;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    @Override
    public String toString() {
        return "SetBean{" +
                "username='" + username + ''' +
                ", age=" + age +
                ", password='" + password + ''' +
                ", listHouse=" + listHouse +
                '}';
    }
}

构造注入,xml的配置中添加constructor-arg标签，并且需要设置参数位置如index=“0”,表示构造函数的第一个参数，如下：

java文件中必须要有与xml文件一样的构造方法。如下：

package com.xyj.demo;

import java.util.List;

public class ContructorBean {
    private String username;
    private int age;
    private String password;
    private List listHouse;
    public ContructorBean(){
        super();
    }
    public ContructorBean(String username, int age, String password, List listHouse) {
        this.username = username;
        this.age = age;
        this.password = password;
        this.listHouse = listHouse;
    }

    @Override
    public String toString() {
        return "ContructorBean{" +
                "username='" + username + ''' +
                ", age=" + age +
                ", password='" + password + ''' +
                ", listHouse=" + listHouse +
                '}';
    }
}

基于annotation的装配

使用@Component,@Repository,@Service,@Controller

其中：component，repository，service，controller作用是一样的，只是为了清楚的区分不同的bean的功能或者所属层

@autowired,@Resource,@Qualifier

其中autowired和resource作用是一样的，表示依赖注入，qualifier是配合autowired使用

创建bean1.xml配置文件,使用了****标签

package com.com.xyj.annotationDemo;

import org.springframework.stereotype.Component;

@Component("useDAO")
public class UseDAO {
    public void login(){
        System.out.println("useDao login..");
    }
}

package com.com.xyj.annotationDemo;

import org.springframework.stereotype.Component;
import org.springframework.stereotype.Service;

import javax.annotation.Resource;

@Service("useService")
public class UseService {
    @Resource(name="useDAO")
    private UseDAO useDAO;
    
    public void login(){
        useDAO.login();
        System.out.println("UseService login....");
    }
}

package com.com.xyj.annotationDemo;

import org.springframework.stereotype.Component;

import javax.annotation.Resource;

@Component("userController")
public class UserController {
    @Resource(name="useService")
    private UseService useService;

    public void save(){
        this.useService.login();
        System.out.println("运行UserController save...");
    }
}

测试类

这里的文件路径需要注意两点：1、是target目录下的路径；2、确定xml在里面，好像Rebuild不会把xml文件放加进去

public class Test {
    private static ApplicationContext applicationContext;
    public static void main(String[] args) {
        //定义配置文件路径
        //在class文件路径下需要有这个文件，才不会抛异常
        //否则提示：Caused by: java.io.FileNotFoundException: class path resource [beans1.xml] cannot be opened because it does not exist
        //这个文件是在target下
//        String path="com/com/xyj/annotationDemo/beans1.xml";
        String path="beans1.xml";
        //获取配置对象
         applicationContext = new ClassPathXmlApplicationContext(path);
        UserController userController = (UserController)applicationContext.getBean("userController");
        userController.save();
    }
}

基于自动加载的装配

创建bean2.xml配置文件,添加了autowire属性，并设置未byName，不会用到注解：

一定要为成员设置set方法，否则会提示空指针：Exception in thread “main” java.lang.NullPointerException

java文件如下：

package com.com.xyj.annotationDemo;

import org.springframework.stereotype.Component;

public class UseDAO {
    public void login(){
        System.out.println("useDao login..");
    }
}

package com.com.xyj.annotationDemo;

import org.springframework.stereotype.Component;
import org.springframework.stereotype.Service;

import javax.annotation.Resource;

//@Service("useService")
public class UseService {
//    @Resource(name="useDAO")
    private UseDAO useDAO;
//
    public void setUseDAO(UseDAO useDAO) {
        this.useDAO = useDAO;
    }
    public void login(){
        useDAO.login();
        System.out.println("UseService login....");
    }
}

package com.com.xyj.annotationDemo;

import org.springframework.stereotype.Component;

import javax.annotation.Resource;

//@Component("userController")
public class UserController {
//    @Resource(name="useService")
    private UseService useService;

    public void setUseService(UseService useService) {
        this.useService = useService;
    }

    public void save(){
        this.useService.login();
        System.out.println("运行UserController save...");
    }
}

测试类

package com.com.xyj.annotationDemo;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Test2 {
    public static void main(String[] args) {
        String path ="bean/beans2.xml";
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext(path);
        UserController userController = (UserController)applicationContext.getBean("userController");
        userController.save();
    }
}

Spring中的Bean

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