Spring - 初始化bean

对于Spring框架来说，控制反转（Inversion of Control）和依赖注入（Dependency injection）是其核心，这里通过一个 bean 初始化的过程来理解一下IoC和DI的概念。

# URL
http://www.springsource.org/download/community 
http://static.springsource.org/spring/docs/3.2.x/spring-framework-reference/html/ 

# 依赖 jar
commons-logging-1.1.3.jar
spring-beans-3.2.3.RELEASE.jar
spring-context-3.2.3.RELEASE.jar
spring-core-3.2.3.RELEASE.jar
spring-expression-3.2.3.RELEASE.jar

# 一个最简单的 spring 配置文件 

# src/spring.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"     xsi:schemaLocation="       http://www.springframework.org/schema/beans       http://www.springframework.org/schema/beans/spring-beans.xsd" >        <bean id="person" class="org.demo.bean.Person" />    </beans>

# Java 代码

package org.demo.bean;import java.util.Map;import java.util.Properties;import java.util.Set;public class Person {private boolean propBool;private byte propByte;private short propShort;private int propInt;private long propLong;private float propFloat;private double propDouble;private String propStr;private Set<String> propSet;private Map<String, String> propMap;private Properties props;private String propSystemProp;private String propSystemEnv;/** get set methods */}

# 测试代码

package org.demo;import org.demo.bean.Person;import org.springframework.context.support.AbstractApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;public class Main {public static void main(String[] args) {AbstractApplicationContext ctx = new ClassPathXmlApplicationContext("spring.xml");Person p1 = ctx.getBean(Person.class);     // 通过类型来获取 beanPerson p2 = (Person)ctx.getBean("person"); // 通过 id来获取 beanSystem.out.println(p1);System.out.println(p2);}}

# 这里获取到的 p1、p2 是同一个实例，因为 spring 容器中的 bean 默认是单例，也就是 singleton，如果需要每次调用 getBean 得到的都是不同的实例，则需要将 bean 的 scope 属性设置成 prototype ，如下：

<bean id="person" class="org.demo.bean.Person" scope="prototype" />

# 设置 bean 的属性值

<?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" >        <context:property-placeholder />        <bean id="person" class="org.demo.bean.Person">        <property name="propBool" value="true" />        <property name="propByte" value="1" />        <property name="propShort" value="2" />        <property name="propInt" value="3" />        <property name="propLong" value="4" />        <property name="propFloat" value="5.0" />        <property name="propDouble" value="6.2" />        <property name="propStr" value="zhangSan" />        <property name="propSet">            <set>                <value>10</value>                <value>12</value>            </set>        </property>        <property name="propMap">            <map>                <entry key="key1" value="value1" />                <entry key="key2" value="value2" />            </map>        </property>        <property name="props">            <props>                <prop key="propKey1">propValue1</prop>                <prop key="propKey2">propValue2</prop>            </props>        </property>        <property name="propSystemProp" value="${java.io.tmpdir}" />        <property name="propSystemEnv" value="${JAVA_HOME}" />    </bean>    </beans>

# 注意：通过 ${propertyName} 这种方式不仅可以引用JVM的系统属性（在JVM启动的时候通过参数 -DpropertyName=propertyValue 进行设置），还可以引用操作系统的环境变量（例如 windows 中的 系统属性 -> 高级 -> 环境变量 -> 系统变量）。使用 ${...} 时需要配置有 <context:property-placeholder />，否则${...} 将当成普通字符串进行处理。

# 注入依赖对象
# 方案一（通过<property> 元素来注入依赖对象）

package org.demo.service;import org.demo.bean.Person;public class PersonService {private Person person;/** get set methods */}

<?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="person" class="org.demo.bean.Person">        <property name="propStr" value="zhangSan" />    </bean>        <bean id="personService" class="org.demo.service.PersonService" >        <property name="person" ref="person" />    </bean>    </beans>

# 方案二（通过@Autowired注解来注入依赖对象）

package org.demo.service;import org.demo.bean.Person;import org.springframework.beans.factory.annotation.Autowired;public class PersonService {    @Autowiredprivate Person person;    /** get set methods */}

<?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" >        <!-- 这里表示启用注解，例如： -->    <!--  @Repository、@Service、@Controller、@Component、@Autowired、@Resource -->    <context:annotation-config />        <bean id="person" class="org.demo.bean.Person">        <property name="propStr" value="zhangSan" />    </bean>        <bean id="personService" class="org.demo.service.PersonService" />    </beans>

# 方案三（通过@Resource注解来注入依赖对象）

@Resourceprivate Person person;

# 注入 ApplicationContext
# 方案一（通过 @Autowired/@Resource 注解来注入）

@Resource// @Autowiredprivate ApplicationContext ctx;

# 方案二（通过实现接口 ApplicationContextAware 来注入）

package org.demo.service;import org.springframework.beans.BeansException;import org.springframework.context.ApplicationContext;import org.springframework.context.ApplicationContextAware;public class PersonService implements ApplicationContextAware {    private ApplicationContext ctx;    @Overridepublic void setApplicationContext(ApplicationContext pCtx)throws BeansException {this.ctx = pCtx;}/** get set methods */}

其他 Aware 接口请参阅：http://static.springsource.org/spring/docs/3.2.x/spring-framework-reference/html/beans.html#aware-list  

# bean 的生命周期 - 在初始化 bean 的过程中执行一段自定义的代码
# 方案一（通过@PostConstruct 注解来实现）

@PostConstructpublic void postConstruct() {System.out.println("-- postConstruct --");}

# 方案二（通过接口 InitializingBean 来实现）

public class PersonService implements InitializingBean{    @Overridepublic void afterPropertiesSet() throws Exception {System.out.println("-- afterPropertiesSet --");}}

# 方案三（通过在 spring 配置文件中指定一个初始化方法来实现）

    <bean id="personService"           class="org.demo.service.PersonService" init-method="init" />

或者

<?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-init-method="init2">    <!-- ... --></beans>

# bean 的生命周期 - 在销毁 bean 之前执行一段自定义的代码
# 与初始化过程中对应的依次为：@PreDestroy注解、DisposableBean接口、destroy-method/default-destroy-method

# bean 的生命周期 - SmartLifecycle

package org.demo.service;import org.springframework.context.SmartLifecycle;public class PersonService implements SmartLifecycle {    private boolean isRunning = false;@Overridepublic boolean isAutoStartup() {System.out.println("-- isAutoStartup --");return true;}@Overridepublic int getPhase() {System.out.println("-- getPhase --");return -1;}@Overridepublic boolean isRunning() {System.out.println("-- isRunning " + isRunning + " --");return isRunning;}    @Overridepublic void start() {isRunning = true;System.out.println("-- start --");}@Overridepublic void stop(Runnable stopCallback) {System.out.println("-- stop runnable --");stopCallback.run();isRunning = false;}    @Overridepublic void stop() {System.out.println("-- stop --");}}

详细信息请参阅：http://static.springsource.org/spring/docs/3.2.x/spring-framework-reference/html/beans.html#beans-factory-lifecycle-processor

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