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spring web-mvc衍生注解

深浅Java 人气:0

衍生注解

在web开发中,会根据webmvc的三层加购分层,这时候每层都有相同一个不同的注解名字,但功能都相同。

注解:使用了注解之后,在容器中不需要注入bean,但要指定查找的的项目。

容器配置

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        https://www.springframework.org/schema/context/spring-context.xsd">
      <!--指定注入时需要查找的项目-->
       <context:component-scan base-package="com.yc.ch"/>
</beans>

创建一个dao层和一个组件归类层,文件样式如下

dao和pojo

User类

import com.yc.dao.Userdao;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
//该注释表示注册到容器中,直接由spring容器托管,
@Component
public class User {
    //表示设置name的参数值为为Tom
    //等价于 <property name="name" value="Tom"/>
    @Value("Tom")
    private String name;
    private Userdao userdao;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Userdao getUserdao() {
        return userdao;
    }
    public void setUserdao(Userdao userdao) {
        this.userdao = userdao;
    }
    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", userdao=" + userdao +
                '}';
    }
}

Userdao类

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Repository;
//该注释表示注册到容器中,直接由spring容器托管,
@Repository
public class Userdao {
    //表示设置name的参数值为为游泳
    //等价于 <property name="name" value="游泳"/>
    @Value("游泳")
    private  String name;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public String toString() {
        return "Userdao{" +
                "name='" + name + '\'' +
                '}';
    }
}

spring容器配置

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        https://www.springframework.org/schema/context/spring-context.xsd">
        
       <!--表示查找到com.yc下的所有层-->
       <context:component-scan base-package="com.yc"/>
</beans>

创建测试类

ApplicationContext context=new ClassPathXmlApplicationContext("beans.xml");
User u=context.getBean("user",User.class);
System.out.println(u);

输出

User{name=‘Tom’, userdao=null}

最终输出的只有User类,但是Userdao层次却直接显示空,问题是没有把Userdao的bean引入到User的bean中,所以在测试User类时显示空。解决:使用使用注解 @Autowired方式匹配到Userdao中

将User类修改

import com.yc.dao.Userdao;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
@Component
public class User {
    @Value("Tom")
    private String name;
    @Autowired
    private Userdao userdao;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Userdao getUserdao() {
        return userdao;
    }
    public void setUserdao(Userdao userdao) {
        this.userdao = userdao;
    }
    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", userdao=" + userdao +
                '}';
    }
}

修改spring容器配置

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        https://www.springframework.org/schema/context/spring-context.xsd">
       <context:component-scan base-package="com.yc"/>
       <context:annotation-config/>
</beans>

创建测试类,输出

User{name=‘Tom’, userdao=Userdao{name=‘游泳’}}

@Component使用

@Component还可以加参数,里面值相当于注入bean中的id值,上面的案例默认为User类的小写user,如果设置为@Component(value = “user2”)或者@Component(“user2”),则将测试类改写为

  ApplicationContext context=new ClassPathXmlApplicationContext("beans.xml");
        User u=context.getBean("user2",User.class);
        System.out.println(u);

以上为个人经验,希望能给大家一个参考,也希望大家多多支持。 

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