6.装配Bean

其他 2018-10-21 05:13:24 阅读次数: 0

文章目录

6.装配Bean

装配方案

  1. 基于xml
  2. 基于java
  3. 基于隐式地bean发现与自动装配

通过自动化装配

  1. 优点

    1. 便利，自动化，可以解决大部分问题

  2. Spring从两个角度来实现自动转配

    1. 组件扫描(component scan)

      1. xml

        <context:component-scan base-package="com.desmond"/>

      2. @component

    2. 自动装配(autowiring)

  3. @ComponentScan 默认扫描与该配置类相同的基础包，i.e. @ComponentScan配置在那个package的类下面，就扫描该package.

  4. @ComponentScan可以指定多个扫描路径

  5. @ComponentScan可以使用 Class或者字符串路径 来指定base package路径：class路径：

    @Configuration
@ComponentScan(basePackageClasses = com.desmond.springlearning.scan.Human.class)
public class Man {
    @Autowired
    private Human human;

    public void sayHi() {
        human.sayHi();
    }
}

    或者 字符串路径：

    @ComponentScan(basePackages = "com.desmond.springlearning.scan")

    或者 两者组合：

    @Configuration
@ComponentScans({
        @ComponentScan(basePackageClasses = com.desmond.springlearning.scan.Human.class),
        @ComponentScan(basePackages = "com.desmond.springlearning.scan")
})

    Class 路径比字符路径更安全(字符串路径可能会出错，尽快有IDE的辅助检查)，对重构也更加友好，可以创建一个接口，只是用来指定base package即可。

通过Java代码装配

  1. 相比XML, 对重构更加友好，更加安全(Class类比xml 字符串更不容出错)，类型安全。

  2. 可以自定义bean的实例化,e.g.

    @Configuration
public class Db1Configuration {
    @Bean
    public DbConnection connection() {
        DbConnection conn = new DbConnection("con1")
        // 可以自定义一大堆逻辑
       
        return new DbConnection("con1");
    }
}

    而简单的xml 不具体这样的自定义功能:

    <bean class="com.desmond.springlearning.scan.mixed.DbConnection"/>

    ，但是可以通过factory-method来达到同样的目的

    <bean id="fb" class="com.desmond.springlearning.scan.mixed.DbConnectionFactory"/>
<bean id="factoryConn" factory-bean="fb" factory-method="createDbConnection"/>

    public class DbConnectionFactory {
    public DbConnection createDbConnection() {
        DbConnection connection = new DbConnection();
        connection.setName("from factory.");

        // other logic

        return connection;
    }
}

  3. 当度配置Java config包，已使他与业务代码隔离

通过XML装配

  1. 最成熟、功能最强大
  2. 基于constructor初始化
  3. 基于setter初始化

导入和混合装配

  1. Java config 组合其他config

    1. 一个 @Configuration相当于一个xml 配置文件，可以导入其他xml:

      @Configuration
public class Db1Configuration {
    @Bean
    public DbConnection connection() {
        return new DbConnection("con1");
    }
}

      public class Db2Configuration {
    @Bean
    public DbConnection connection() {
        return new DbConnection("con2");
    }
}


      @Configuration
@Import({Db2Configuration.class, Db1Configuration.class})
public interface CombinationConfiguration {
}

      public class Test {
    public static void main(String[] args) {
        ApplicationContext applicationContext = new AnnotationConfigApplicationContext(CombinationConfiguration.class);

        DbConnection connection = (DbConnection)applicationContext.getBean("connection");
        connection.sayHi();
    }

      如果 Db1Configuration、Db2Configuration有同名的bean,则后方会覆盖前者

    2. java config引入xml配置
      xml

      <bean id="conn2" class="com.desmond.springlearning.scan.mixed.DbConnection" p:name="I'm db2 from xml."/>

      Configuration:

      @Configuration
@Import(Db1Configuration.class)
@ImportResource("classpath:scan/db2Connection.xml")
public class CombinationWithXml {
}

    3. xml中引入java config

      java

      package com.desmond.springlearning.scan.mixed;

import com.desmond.springlearning.scan.Human;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * @author presleyli
 * @date 2018/9/26 上午6:45
 */
@Configuration
public class Db1Configuration {
    @Bean(name = "conn1")
    public DbConnection connection() {
        return new DbConnection("conn1");
    }
}

      db2Connection.xml

      <?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"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd       http://www.springframework.org/schema/task http://www.springframework.org/schema/task/spring-task.xsd http://www.springframework.org/schema/cache http://www.springframework.org/schema/cache/spring-cache.xsd"
        default-autowire="default">

    <bean id="conn2" class="com.desmond.springlearning.scan.mixed.DbConnection" p:name="conn2"/>


</beans>

      Xmlcomb.xml, 注意开启注解驱动：<context:annotation-config/>

      <?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 http://www.springframework.org/schema/beans/spring-beans.xsd 
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd "
       default-autowire="default">

    <context:annotation-config/>

    <bean class="com.desmond.springlearning.scan.mixed.Db1Configuration"/>

    <import resource="db2Connection.xml"/>

</beans>

      测试类

      package com.desmond.springlearning.scan.mixed;

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * @author presleyli
 * @date 2018/9/26 上午6:49
 */
public class TestJavaFromXml {
    public static void main(String[] args) {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("scan/xmlcomb.xml");

        DbConnection connection = (DbConnection)applicationContext.getBean("conn1");
        connection.sayHi();

        connection = (DbConnection)applicationContext.getBean("conn2");
        connection.sayHi();
    }
}

      结果：

      objc[14480]: Class JavaLaunchHelper is implemented in both /Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/bin/java (0x1017fd4c0) and /Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/libinstrument.dylib (0x1018814e0). One of the two will be used. Which one is undefined.
九月 26, 2018 7:52:44 上午 org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@1a86f2f1: startup date [Wed Sep 26 07:52:44 CST 2018]; root of context hierarchy
九月 26, 2018 7:52:45 上午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [scan/xmlcomb.xml]
九月 26, 2018 7:52:45 上午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [scan/db2Connection.xml]

I'm conn1
I'm conn2

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