Spring-引用Bean的属性值

概述

将应用系统的配置信息存放在配置文件中并非总是最合适的，如果应用以集群的方式部署，或者希望在运行期动态调整引用的某些配置，这时，将配置信息放到数据库中不但方便集中管理，而且可以通过应用系统的管理界面动态维护，有效增强应用系统的可维护性。

早期版本，如果想在配置文件中引用另外一个Bean的属性值是比较麻烦的，Spring3.0则提供了优雅的解决方案. 在Spring3.0中，可以通过类似 #{beanName.beanPro}的方式方便的引用另外一个Bean的值。

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实例

代码已托管到Github—> https://github.com/yangshangwei/SpringMaster

假设数据库中有张TEMP_SYS_CONFIG表，数据如下

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基于XML方式的引用

beans.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"    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">    <!-- 扫描类包，将标注Spring注解的类自动转化Bean，同时完成Bean的注入  扫描@Autowired -->    <context:component-scan base-package="com.xgj.ioc.refOtherBeanProByXml"/>    <!-- 定义Bean,通过initFromDB初始化方法从数据库中加载数据 -->    <bean id="sysConfig" class="com.xgj.ioc.refOtherBeanProByXml.SysConfig"         init-method="initFromDB"/>    <!-- 引用sysConfig Bean的属性值 -->    <bean id="applicationManager" class="com.xgj.ioc.refOtherBeanProByXml.ApplicationManager"        p:sessionTimeout="#{sysConfig.sessionTimeout}"        p:maxTabPageNum="#{sysConfig.maxTabPageNum}"/>    <!-- 使用context命名空间 引入外部属性文件 -->     <context:property-placeholder location="classpath:spring/jdbc.properties" />    <!-- 通过属性名引用属性值 -->         <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"        destroy-method="close"        p:driverClassName="${jdbc.driverClassName}"        p:url="${jdbc.url}"        p:username="${jdbc.username}"        p:password="${jdbc.password}"/>    <!-- 配置Jdbc模板  -->    <bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate"        p:dataSource-ref="dataSource" /></beans>

SysConfig.java

package com.xgj.ioc.refOtherBeanProByXml;import java.sql.ResultSet;import java.sql.SQLException;import java.util.ArrayList;import java.util.List;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.jdbc.core.JdbcTemplate;import org.springframework.jdbc.core.RowCallbackHandler;public class SysConfig {    public int sessionTimeout;    public int maxTabPageNum;    private JdbcTemplate jdbcTemplate;    @Autowired    public void setJdbcTemplate(JdbcTemplate jdbcTemplate) {        this.jdbcTemplate = jdbcTemplate;    }    /**     *      *      * @Title: initFromDB     *      * @Description: 从数据库中初始化sessionTimeout和maxTabPageNum属性     *      *      * @return: void     */    public void initFromDB() {        System.out.println("initFrom DB");        final List<String> paramList = new ArrayList<String>();        String sql = " select  value  from TEMP_SYS_CONFIG a where a.code in ('sessionTimeout' ,'maxTabPageNum') ";        jdbcTemplate.query(sql, new RowCallbackHandler() {            @Override            public void processRow(ResultSet rs) throws SQLException {                paramList.add(rs.getString("value"));            }        });        sessionTimeout = Integer.parseInt(paramList.get(0));        maxTabPageNum = Integer.parseInt(paramList.get(1));    }}

ApplicationManager.java

package com.xgj.ioc.refOtherBeanProByXml;public class ApplicationManager {    private int sessionTimeout;    private int maxTabPageNum;    public int getSessionTimeout() {        System.out.println("sessionTimeout:" + sessionTimeout);        return sessionTimeout;    }    public void setSessionTimeout(int sessionTimeout) {        this.sessionTimeout = sessionTimeout;    }    public int getMaxTabPageNum() {        System.out.println("maxTabPageNum:" + maxTabPageNum);        return maxTabPageNum;    }    public void setMaxTabPageNum(int maxTabPageNum) {        this.maxTabPageNum = maxTabPageNum;    }}

测试类

package com.xgj.ioc.refOtherBeanProByXml;import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;public class BeanPropReferenceTest {    public static void main(String[] args) {        ApplicationContext ctx = new ClassPathXmlApplicationContext(                "classpath:com/xgj/ioc/refOtherBeanProByXml/beans.xml");        ApplicationManager applicationManager = ctx.getBean(                "applicationManager", ApplicationManager.class);        applicationManager.getSessionTimeout();        applicationManager.getMaxTabPageNum();    }}

运行结果：

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基于注解的引用

在基于注解和基于JAVA类配置的Bean中，可以通过@Value(“#{beanName.beanPro}”)的注解形式引用Bean的属性值

通过在配置文件中配置context:component-scan ，扫描标注了注解的POJO，实例化并缓存。

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"    xmlns:p="http://www.springframework.org/schema/p"    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">    <!-- 扫描类包，将标注Spring注解的类自动转化Bean，同时完成Bean的注入 -->    <context:component-scan base-package="com.xgj.ioc.refOtherBeanPro"/>    <!-- 使用context命名空间 引入外部属性文件 -->     <context:property-placeholder location="classpath:spring/jdbc.properties" />    <!-- 通过属性名引用属性值 -->         <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"        destroy-method="close"        p:driverClassName="${jdbc.driverClassName}"        p:url="${jdbc.url}"        p:username="${jdbc.username}"        p:password="${jdbc.password}"/>    <!-- 配置Jdbc模板  -->    <bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate"        p:dataSource-ref="dataSource" /></beans>

SysConfig.java

package com.xgj.ioc.refOtherBeanPro;import java.sql.ResultSet;import java.sql.SQLException;import java.util.ArrayList;import java.util.List;import javax.annotation.PostConstruct;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.jdbc.core.JdbcTemplate;import org.springframework.jdbc.core.RowCallbackHandler;import org.springframework.stereotype.Component;@Componentpublic class SysConfig {    public int sessionTimeout;    public int maxTabPageNum;    private JdbcTemplate jdbcTemplate;    @Autowired    public void setJdbcTemplate(JdbcTemplate jdbcTemplate) {        this.jdbcTemplate = jdbcTemplate;    }    /**     *      *      * @Title: initFromDB     *      * @Description: 从数据库中初始化sessionTimeout和maxTabPageNum属性     *      *      * @return: void     */    @PostConstruct    public void initFromDB() {        System.out.println("initFrom DB");        final List<String> paramList = new ArrayList<String>();        String sql = " select  value  from TEMP_SYS_CONFIG a where a.code in ('sessionTimeout' ,'maxTabPageNum') ";        jdbcTemplate.query(sql, new RowCallbackHandler() {            @Override            public void processRow(ResultSet rs) throws SQLException {                paramList.add(rs.getString("value"));            }        });        sessionTimeout = Integer.parseInt(paramList.get(0));        maxTabPageNum = Integer.parseInt(paramList.get(1));    }}

ApplicationManager.java

package com.xgj.ioc.refOtherBeanPro;import org.springframework.beans.factory.annotation.Value;import org.springframework.stereotype.Component;@Componentpublic class ApplicationManager {    private int sessionTimeout;    private int maxTabPageNum;    public int getSessionTimeout() {        System.out.println("sessionTimeout:" + sessionTimeout);        return sessionTimeout;    }    @Value("#{sysConfig.sessionTimeout}")    public void setSessionTimeout(int sessionTimeout) {        this.sessionTimeout = sessionTimeout;    }    public int getMaxTabPageNum() {        System.out.println("maxTabPageNum:" + maxTabPageNum);        return maxTabPageNum;    }    @Value("#{sysConfig.maxTabPageNum}")    public void setMaxTabPageNum(int maxTabPageNum) {        this.maxTabPageNum = maxTabPageNum;    }}

测试类

package com.xgj.ioc.refOtherBeanPro;import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;public class BeanPropReferenceTest {    public static void main(String[] args) {        ApplicationContext ctx = new ClassPathXmlApplicationContext(                "classpath:com/xgj/ioc/refOtherBeanPro/beans.xml");        ApplicationManager applicationManager = ctx.getBean(                "applicationManager", ApplicationManager.class);        applicationManager.getSessionTimeout();        applicationManager.getMaxTabPageNum();    }}

运行结果：