Spring的配置（使用注解）

一、配置步骤

1. 为主配置文件引入新的命名空间（约束）

   context

   
   <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 http://www.springframework.org/schema/beans/spring-beans-3.0.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
   
   beans>

2. 开启使用注解代理配置文件

   
   <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 http://www.springframework.org/schema/beans/spring-beans-3.0.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
   
      
      <context:component-scan base-package="cn.jjs.bean">context:component-scan>
   
   beans>

3. 在类中使用注解，完成配置

   使用@component将User类配置到Spring容器中

   package cn.jjs.bean;
   
   import org.springframework.stereotype.Component;
   
   @Component("user")
   public class User {
      private String name;
      private Integer age;
      private Car car;
   
      public Car getCar() {
          return car;
      }
   
      public void setCar(Car car) {
          this.car = car;
      }
   
      public String getName() {
          return name;
      }
   
      public void setName(String name) {
          this.name = name;
      }
   
      public Integer getAge() {
          return age;
      }
   
      public void setAge(Integer age) {
          this.age = age;
      }
   
      @Override
      public String toString() {
          return "User{" +
                  "name='" + name + '\'' +
                  ", age=" + age +
                  ", car=" + car +
                  '}';
      }
   }

   其中@component(“user”)相当于XML中的

   测试类：

   package cn.jjs.a_annocation;
   
   import cn.jjs.bean.User;
   import org.junit.Test;
   import org.springframework.context.ApplicationContext;
   import org.springframework.context.support.ClassPathXmlApplicationContext;
   
   public class Demo {
      @Test
      public void test() {
          ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
          User u = (User)ac.getBean("user");
          System.out.println(u);
      }
   }

   结果：

   User{name='null', age=null, car=null}

二、其他对象注册注解

推荐使用，可以体现分层的下列注解将对象注册到容器

• @Service service层
• @Controller Web层
• @Repository Dao层

@scope

@Scope(scopeName = "prototype|singleton")

默认为singleton，单例

prototype，多例

@value 值类型注入

@Component("user")

public class User {
    @Value("Tom")
    private String name;
    private Integer age;
    private Car car;

    public Car getCar() {
        return car;
    }

    public void setCar(Car car) {
        this.car = car;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", car=" + car +
                '}';
    }
}

@Value可以加在name属性上，也可以加在setName()方法上。

在name成员变量上，通过反射的Field赋值（破坏了对象的封装性），

在setName()方法上，通过set方法赋值。

@Autowired 引用类型注入

自动装配，用于引用类型

User.java
package cn.jjs.bean;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component("user")

public class User {
    @Value("Tom")
    private String name;
    private Integer age;
    @Autowired
    private Car car;

    public Car getCar() {
        return car;
    }

    public void setCar(Car car) {
        this.car = car;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", car=" + car +
                '}';
    }
}

Car.java
package cn.jjs.bean;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component("car")
public class Car {
    private String name;
    private String color;

    public String getName() {
        return name;
    }
    @Value("Honda")
    public void setName(String name) {
        this.name = name;
    }

    public String getColor() {
        return color;
    }
    @Value("Red")
    public void setColor(String color) {
        this.color = color;
    }

    @Override
    public String toString() {
        return "Car{" +
                "name='" + name + '\'' +
                ", color='" + color + '\'' +
                '}';
    }
}

结果：

User{name='Tom', age=null, car=Car{name='Honda', color='Red'}}

问题：如果匹配多个类型一致的对象，将无法选择具体注入哪个对象。

比如在applicationContext.xml中再配置一个Car

<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 http://www.springframework.org/schema/beans/spring-beans-3.0.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">

    
    <context:component-scan base-package="cn.jjs.bean">context:component-scan>

    <bean name="car2" class="cn.jjs.bean.Car">
        <property name="name" value="WV">property>
        <property name="color" value="black">property>
    bean>
beans>

使用@Qualifier(“car2”)注解告诉Spring容器自动装配哪个对象，与@Autowired成对使用。

package cn.jjs.bean;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component("user")
public class User {
    @Value("Tom")
    private String name;
    private Integer age;

    @Autowired
    @Qualifier("car2")
    private Car car;

    public Car getCar() {
        return car;
    }

    public void setCar(Car car) {
        this.car = car;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", car=" + car +
                '}';
    }

结果：

User{name='Tom', age=null, car=Car{name='WV', color='black'}}

@Autowired与@Qualifier(“car2”)成对使用太啰嗦，使用@Resource(name = “car2”)可以替代。

手动注入，指定注入哪个名称的对象。

package cn.jjs.bean;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

import javax.annotation.Resource;

@Component("user")

public class User {
    @Value("Tom")
    private String name;
    private Integer age;

    @Resource(name = "car2")
    private Car car;

    public Car getCar() {
        return car;
    }

    public void setCar(Car car) {
        this.car = car;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", car=" + car +
                '}';
    }

@PostConstruct

在User.java中，

    @PostConstruct
    public void init() {
        System.out.println("init()");
    }

注明，在对象创建后立即调用。

相当于XML中的：init-method

@PreDestroy

在User.java中，

    @PreDestroy
    public void destroy() {
        System.out.println("destroy");
    }

注明，在对象销毁前调用。

相当于XML中的：destroy-method