如何在 applicationContext.xml 中有条件地使用数据源

Question

我正在使用 Spring 创建一个 GAE 项目，该项目也将使用云 SQL。在本地测试此应用程序时，我指向我的本地 MySQL 环境，但是当我将其部署到 GAE 时，它将指向云 SQL 实例。所以我想根据环境在数据源 bean 中配置我的 driverName。为此，我们通常在我们的 java 代码中使用以下代码

if (SystemProperty.environment.value() == SystemProperty.Environment.Value.Production) {
    // Load the class that provides the new "jdbc:google:mysql://" prefix.
    Class.forName("com.mysql.jdbc.GoogleDriver");
    url = "jdbc:google:mysql://<your-project-id>:<your-instance-name>/<your-database-name>?user=root";
} else {
    // Local MySQL instance to use during development.
    Class.forName("com.mysql.jdbc.Driver");
    url = "jdbc:mysql://127.0.0.1:3306/<your-database-name>?user=root";
}

现在我想使用 Spring Expression 语言在 applicationcontext.xml 中实现相同的目的。我以前没有这样做过，也无法实现。请指导我。这是我尝试过的

<bean id="isDev" class="java.lang.Boolean">
    <constructor-arg value="#{ systemProperties[environment.value] == SystemProperty.Environment.Value.Development ? true : false }" />
</bean>

<bean id="dataSource"
    class="org.springframework.jdbc.datasource.DriverManagerDataSource">
    <property name="driverClassName" value="#{ isDev ? com.mysql.jdbc.Driver : com.mysql.jdbc.GoogleDriver }" />
.
.
.

但是我遇到了异常，附加了一部分异常

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'feedbackFormController': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: com.sandeepapplabs.custengage.services.FeedbackFormService com.sandeepapplabs.custengage.controllers.FeedbackFormController.feedbackFormService; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'feedbackFormService': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: com.sandeepapplabs.custengage.daos.FeedbackFormDAO com.sandeepapplabs.custengage.services.impl.FeedbackFormServiceImpl.feedbackFormDAO; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'feedbackFormDAO' defined in ServletContext resource [/WEB-INF/custengage-servlet.xml]: Cannot resolve reference to bean 'dataSource' while setting bean property 'dataSource'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource' defined in ServletContext resource [/WEB-INF/custengage-servlet.xml]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanExpressionException: Expression parsing failed; nested exception is org.springframework.beans.factory.BeanExpressionException: Expression parsing failed; nested exception is java.lang.NullPointerException

Answer 1

我相信您需要引用类名以使其成为文字...

... 'com.mysql.jdbc.Driver' ...

但是使用 Spring Profiles](http://docs.spring.io/spring-framework/docs/current/spring-framework-reference/html/beans.html#beans-definition-profiles-xml) 并启用所需的配置文件会更容易。

Answer 2

您可以使用 Spring 配置文件来更改具体的 bean 类。假设您有 2 个配置文件：“prod”和“dev”。你的 bean 方法应该有 @Profile 注释，如下所示：

@Configuration
public class AppConfig {

...

  @Bean
  @Profile("prod")
  public Object prodDataSource() { 

    return new ...
  }

  @Bean
  @Profile("dev")
  public Object getDataSource() throws Exception {
    return new ...
  }

 }

如果你使用的是Maven，可以通过pom.xml选择profile：

<profiles>
    <profile>
        <id>dev</id>
        <activation>
            <activeByDefault>true</activeByDefault>
        </activation>
        <properties>
            <spring.profile>dev</spring.profile>
        </properties>
    </profile>

    <profile>
        <id>prod</id>
        <activation>
            <activeByDefault>false</activeByDefault>
            <property>
                <name>prod</name>
            </property>
        </activation>
        <properties>
            <spring.profile>prod</spring.profile>
        </properties>
    </profile>

</profiles>

您可以通过-D 传递配置文件选择参数，例如：mvn -Dprod clean compile test install

编辑：

在application.properties 以下属性选择配置文件：

spring.profiles.active=${spring.profile}