Spring中Bean的作用域和自动装配方式

Bean的作用域

Spring中bean的作用域共有singleton、prototype、request、session、application、websocket六种

其中后四种都是用在Web应用程序中的，主要介绍前两种singleton(单例)和prototype(原型)

Bean的作用域范围为singleton时，所有实例共享一个对象。

Spring的默认配置为scope = “singleton”，以下两种配置的效果是一样的：

默认配置

<?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:p="http://www.springframework.org/schema/p"
     xmlns:c="http://www.springframework.org/schema/c"
     xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
  <!--Spring默认配置为scope = "singleton"-->
  <bean id = "user" class="indi.stitch.pojo.User" />
</beans>

scope = “singleton”

<?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:p="http://www.springframework.org/schema/p"
     xmlns:c="http://www.springframework.org/schema/c"
     xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
  <!--Spring默认配置为scope = "singleton"-->
  <bean id = "user" class="indi.stitch.pojo.User" scope = "singleton" />
</beans>

测试类及输出结果：

import indi.stitch.pojo.User;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class MyTest {
  
  @Test
  public void test2() {
      ApplicationContext context = new ClassPathXmlApplicationContext("namespace.xml");
      User user = context.getBean("user", User.class);
      User user2 = context.getBean("user", User.class);
      System.out.println(user == user2);
  }
}

Spring中Bean的作用域和自动装配方式

scope = “prototype”

<?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:p="http://www.springframework.org/schema/p"
     xmlns:c="http://www.springframework.org/schema/c"
     xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
  <!--Spring默认配置为scope = "singleton"-->
  <bean id = "user" class="indi.stitch.pojo.User" scope = "prototype" />
</beans>

测试类及输出结果：

import indi.stitch.pojo.User;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class MyTest {
  @Test
  public void test2() {
      ApplicationContext context = new ClassPathXmlApplicationContext("namespace.xml");
      User user = context.getBean("user", User.class);
      User user2 = context.getBean("user", User.class);
      System.out.println(user == user2);
  }
}

Spring中Bean的作用域和自动装配方式

Bean的自动装配

Spring中Bean的自动装配基于autowired标签实现

首先创建实体类People、Cat、Dog，People和Cat、Dog是组合关系，People中定义了依赖于Cat、Dog的属性

People实体类

package indi.stitch.pojo;
public class People {
  private Cat cat;
  private Dog dog;
  public Cat getCat() {
      return cat;
  }
  public void setCat(Cat cat) {
      this.cat = cat;
  }
  public Dog getDog() {
      return dog;
  }
  public void setDog(Dog dog) {
      this.dog = dog;
  }
  @Override
  public String toString() {
      return "People{" +
              "cat=" + cat +
              ", dog=" + dog +
              '}';
  }
}

Cat实体类

package indi.stitch.pojo;
public class Cat {
  public void shout() {
      System.out.println("miao~");
  }
}

Dog实体类

package indi.stitch.pojo;
public class Dog {
  public void shout() {
      System.out.println("wang~");
  }
}

通过name自动装配

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
  <bean id = "cat" class="indi.stitch.pojo.Cat" />
  <bean id = "dog" class="indi.stitch.pojo.Dog" />
  <!--在Spring上下文中通过检索name完成自动装配，检索依据为bean中属性的set方法除set部分外的后缀-->
  <bean id = "people" class="indi.stitch.pojo.People" autowire="byName"/>
</beans>

测试类及输出结果：

import indi.stitch.pojo.People;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class MyTest {
  public static void main(String[] args) {
      ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
      People people = context.getBean("people", People.class);
      people.getCat().shout();
      people.getDog().shout();
  }
}

输出结果

Spring中Bean的作用域和自动装配方式

通过type自动装配

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
  <bean id = "cat" class="indi.stitch.pojo.Cat" />
  <bean id = "dog" class="indi.stitch.pojo.Dog" />
  <!--在Spring上下文中通过对属性对应类型进行检索完成自动装配，Spring配置中不能存在被依赖的相同类型的多个bean,被依赖的bean在Spring中配置时可以省略id属性-->
  <bean id = "people" class="indi.stitch.pojo.People" autowire="byType"/>
</beans>

测试类和结果和上面相同

import indi.stitch.pojo.People;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class MyTest {
  public static void main(String[] args) {
      ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
      People people = context.getBean("people", People.class);
      people.getCat().shout();
      people.getDog().shout();
  }
}

输出结果

Spring中Bean的作用域和自动装配方式