浅析Spring IOC 依赖查找你需要知道的几种方式-编程学习网


public class User {

    private long id;
    private String name;

    public long getId() {
        return id;
    }
    public void setId(long id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

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

在 resources 目录下，创建 dependency-look-up.xml 配置文件


<?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
        https://www.springframework.org/schema/beans/spring-beans.xsd">


    <bean id = "user" class="org.example.overview.dependency.domain.User">
        <property name="id" value="1"/>
        <property name="name" value="彭于晏"/>
    </bean>

    <bean id="superUser" class="org.example.overview.dependency.domain.SuperUser" parent="user"
          primary="true">
        <property name="address" value="杭州"/>
    </bean>

    <bean id="objectFactory" class="org.springframework.beans.factory.config.ObjectFactoryCreatingFactoryBean">
        <property name="targetBeanName" value="user"/>
    </bean>

</beans>

1. 根据 Bean 名称查找

实时查找

实时查找的意思就是说直接获取 beanFactory, 通过 beanFactory 获取 user 对应的 bean，代码如下所示


 BeanFactory beanFactory = new ClassPathXmlApplicationContext("classpath:/META-INF/dependency-look-up.xml");
// 这里的 “user” 就是 xml 文件中的 id，即名称实时查找                
User user = (User) beanFactory.getBean("user");
System.out.println("实时加载: " + bean);

延时查找

这里的延迟就是说，通过其他的对象来获取 user 对应的 Bean，代码如下所示：


ObjectFactory<User> objectFactory = (ObjectFactory<User>) beanFactory.getBean("objectFactory");
User user = objectFactory.getObject();
System.out.println("延迟加载" + user);

2. 根据 Bean 类型查找

这里的类型指的就是 user.class

单个 Bean 对象


User bean = beanFactory.getBean(User.class);

集合 Bean 对象


if(beanFactory  instanceof ListableBeanFactory){
      ListableBeanFactory listableBeanFactory = (ListableBeanFactory)beanFactory;
      Map<String, User> beansOfType = listableBeanFactory.getBeansOfType(User.class);
      System.out.println("集合类型：" + beansOfType);
 }

3. 根据 Bean 类型 + 名称查找

4. 根据 Java 注解查找

首先我们自定义一个注解 @Super


@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface Super {
}

将注解表示到 superUser 类中，这里的 superUser 继承了 user 类


@Super
public class SuperUser extends User {

    private String address;

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "SuperUser{" +
                "address='" + address + '\'' +
                "} " + super.toString();
    }
}

最后根据 spring 提供的 api，获取注解 bean


 if(beanFactory  instanceof ListableBeanFactory){
       ListableBeanFactory listableBeanFactory = (ListableBeanFactory)beanFactory;
       Map<String, Object> beansOfType = listableBeanFactory.getBeansWithAnnotation(Super.class);
       System.out.println("查找 @super 的：" + beansOfType);
 }

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浅析Spring IOC 依赖查找你需要知道的几种方式

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