spring4-2-bean配置-6-使用外部属性文件

　　在配置文件里配置 Bean 时, 有时需要在 Bean 的配置里混入系统部署的细节信息(例如: 文件路径, 数据源配置信息等). 而这些部署细节实际上需要和 Bean 配置相分离
Spring 提供了一个 PropertyPlaceholderConfigurer 的 BeanFactory 后置处理器, 这个处理器允许用户将 Bean 配置的部分内容外移到属性文件中. 可以在 Bean 配置文件里使用形式为 ${var} 的变量, PropertyPlaceholderConfigurer 从属性文件里加载属性, 并使用这些属性来替换变量.
Spring 还允许在属性文件中使用 ${propName}，以实现属性之间的相互引用。

一个原始的数据库源配置

1.引入类库-c3p0 和 mysql:

        <dependency>
            <groupId>com.mchange</groupId>
            <artifactId>c3p0</artifactId>
            <version>0.9.5.1</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.35</version>
        </dependency>

 

2.配置ComboPooledDataSource数据源bean实例:

    <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
        <property name="user" value="root"></property>
        <property name="password" value="root"></property>
        <property name="driverClass" value="com.mysql.jdbc.Driver"></property>
        <property name="jdbcUrl" value="jdbc:mysql://127.0.0.1:3306/retrieval?characterEncoding=UTF-8"></property>
    </bean>

 

3.测试：

public class App {

    @SuppressWarnings("resource")
    public static void main(String[] args) throws SQLException {
        ApplicationContext ctx = new ClassPathXmlApplicationContext("beans-properties.xml");
        DataSource ds = ctx.getBean("dataSource",DataSource.class);
        System.out.println(ds.getConnection());
    }

}

 

结果:

六月 18, 2015 10:20:03 上午 org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@2919d975: startup date [Thu Jun 18 10:20:03 CST 2015]; root of context hierarchy
六月 18, 2015 10:20:03 上午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [beans-properties.xml]
六月 18, 2015 10:20:04 上午 com.mchange.v2.log.MLog 
信息: MLog clients using java 1.4+ standard logging.
六月 18, 2015 10:20:04 上午 com.mchange.v2.c3p0.C3P0Registry 
信息: Initializing c3p0-0.9.5.1 [built 16-June-2015 00:06:36 -0700; debug? true; trace: 10]
六月 18, 2015 10:20:04 上午 com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource 
信息: Initializing c3p0 pool... com.mchange.v2.c3p0.ComboPooledDataSource [ acquireIncrement -> 3, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, contextClassLoaderSource -> caller, dataSourceName -> 1bqwdwp9a18ly9s70r2uf|45daddae, debugUnreturnedConnectionStackTraces -> false, description -> null, driverClass -> com.mysql.jdbc.Driver, extensions -> {}, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, forceSynchronousCheckins -> false, forceUseNamedDriverClass -> false, identityToken -> 1bqwdwp9a18ly9s70r2uf|45daddae, idleConnectionTestPeriod -> 0, initialPoolSize -> 3, jdbcUrl -> jdbc:mysql://127.0.0.1:3306/retrieval?characterEncoding=UTF-8, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 0, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 15, maxStatements -> 0, maxStatementsPerConnection -> 0, minPoolSize -> 3, numHelperThreads -> 3, preferredTestQuery -> null, privilegeSpawnedThreads -> false, properties -> {user=******, password=******}, propertyCycle -> 0, statementCacheNumDeferredCloseThreads -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, userOverrides -> {}, usesTraditionalReflectiveProxies -> false ]
com.mchange.v2.c3p0.impl.NewProxyConnection@79af126e [wrapping: com.mysql.jdbc.JDBC4Connection@54e3322b]

 

 

从外部属性文件中读取

1.创建一个属性文件-db.properties

user=root
password=root
driverClass=com.mysql.jdbc.Driver
jdbcUrl=jdbc:mysql://127.0.0.1:3306/retrieval?characterEncoding=UTF-8

 

2.注册 PropertyPlaceholderConfigurer.使其可以从属性文件中加载属性.

首先引入命名空间context.

    <!-- 导入属性文件 -->
    <context:property-placeholder location="classpath:db.properties"/>
    
    <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
        <!-- 使用外部属性文件中的属性 -->
        <property name="user" value="${user}"></property>
        <property name="password" value="${password}"></property>
        <property name="driverClass" value="${driverClass}"></property>
        <property name="jdbcUrl" value="${jdbcUrl}"></property>
    </bean>

 

　　这样就完成部署了.

　　这样做的好处:修改外部属性文件的成本要比修改Spring 配置文件的成本要低的多.