Spring-引用Bean的属性值

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发布于 2021-08-16 08:36:14

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代码可运行

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代码可运行

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。

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

基于XML方式的引用

beans.xml

<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">

    
    <context:component-scan base-package="com.xgj.ioc.refOtherBeanProByXml"/>

    
    <bean id="sysConfig" class="com.xgj.ioc.refOtherBeanProByXml.SysConfig"
         init-method="initFromDB"/>

    
    <bean id="applicationManager" class="com.xgj.ioc.refOtherBeanProByXml.ApplicationManager"
        p:sessionTimeout="#{sysConfig.sessionTimeout}"
        p:maxTabPageNum="#{sysConfig.maxTabPageNum}"/>

    
     <context:property-placeholder location="classpath:spring/jdbc.properties" />

         
    <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}"/>

    
    <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 paramList = new ArrayList();
        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：

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：

<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">

    
    <context:component-scan base-package="com.xgj.ioc.refOtherBeanPro"/>

    
     <context:property-placeholder location="classpath:spring/jdbc.properties" />

         
    <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}"/>

    
    <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;

@Component
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
     */

    @PostConstruct
    public void initFromDB() {
        System.out.println("initFrom DB");
        final List paramList = new ArrayList();
        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;

@Component
public 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();

    }
}