Spring注入，xml方式和注解@Bean

思路：搭建环境，测试xml 和 @configuration的效果，比较写法的不同。

1.新建一个spring空项目。

 2.测试目录下新建测试的资源文件和配置文件。

 3.创建bean类

package com.example.springbean_stu01.bean;

public class UserBean {
    private String Username;
    private String password;
    public UserBean(){
        System.out.println("无参构造");
    };
    public UserBean(String username, String password) {
        System.out.println("有参构造");
        Username = username;
        this.password = password;
    }

    public String getUsername() {
        System.out.println("getUsername");
        return Username;
    }

    public void setUsername(String username) {
        System.out.println("setUsername");
        Username = username;
    }

    public String getPassword() {
        System.out.println("getPassword");
        return password;
    }

    public void setPassword(String password) {
        System.out.println("setPassword");
        this.password = password;
    }
}

 可以从@Bean的源码中看到，name<=>value，默认值就是方法名，这里如果不写name = "userBean"，等价于name ="user"。

4.2写测试类

package com.example.springbean_stu01;

import com.example.springbean_stu01.bean.UserBean;
import com.example.springbean_stu01.configurations.TestConfig;
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

@SpringBootTest
class SpringBeanStu01ApplicationTests {

    @Test
    void contextLoadsByAnnotation() {
        ApplicationContext context = new AnnotationConfigApplicationContext(TestConfig.class);
        UserBean ub = (UserBean) context.getBean("userBean");
        System.out.println(ub.getUsername());
    }

    @Test
    void contextLoadsByXml() {
        ApplicationContext context = new AnnotationConfigApplicationContext(TestConfig.class);
        UserBean ub = (UserBean) context.getBean("user");
        System.out.println(ub.getUsername());
    }

}

运行contextLoadsByAnnotation效果如下

 可以看到，bean被正确的注入了。

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接下来测xml

5.1写配置bean的xml,//testbean.xml

<?xml version="1.0" encoding="UTF-8"?>


    
        User-xml
        123
    

5.2写测试类

package com.example.springbean_stu01;

import com.example.springbean_stu01.bean.UserBean;
import com.example.springbean_stu01.configurations.TestConfig;
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

@SpringBootTest
class SpringBeanStu01ApplicationTests {

    @Test
    void contextLoadsByAnnotation() {
        ApplicationContext context = new AnnotationConfigApplicationContext(TestConfig.class);
        UserBean ub = (UserBean) context.getBean("userBean");
        System.out.println(ub.getUsername());
    }

    @Test
    void contextLoadsByXml() {
        ApplicationContext context = new ClassPathXmlApplicationContext("testbean.xml");
        UserBean ub = (UserBean) context.getBean("userBean");
        System.out.println(ub.getUsername());
    }
}

运行contextLoadsByXml()方法，得到预期的输出如下

 6.总结一波

a.@Configuration配合@Bean，实现无xml自动注入。

b.xml方式写

<bean id="必须唯一，默认类名" class="类的全路径，类必须有无参的构造方法，不然编译报错。">