Spring MVC动态数据源路由给了我空指针异常

如何解决Spring MVC动态数据源路由给了我空指针异常

| 尝试遵循http://blog.springsource.com/2007/01/23/dynamic-datasource-routing/上的代码 但是得到一个讨厌的空指针异常：

//DAO
public class TestDAO extends SimpleJdbcDaoSupport {

public List<Map> getDomains() {
String query = \"select 1 from dual\";
return getSimpleJdbcTemplate().queryForList(query);
}
}

//路由

public class RoutingDataSource extends AbstractRoutingDataSource {
@Override
protected Object determineCurrentLookupKey() {
return SessionContextHolder.getDBServer();
}
}

//控制器

@Controller
@RequestMapping(value=\"/test\")
public class HandleRequest {

@RequestMapping(method=RequestMethod.GET)
public String handle(Model model){

TestDAO testDAO = new TestDAO();

SessionContextHolder.setDBServer(\"server1\");

List domains = testDAO.getDomains();

model.addAttribute(\"domains\",domains);
return \"test1\";
}
}

我的豆子

<?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\"
    xmlns:mvc=\"http://www.springframework.org/schema/mvc\"
    xsi:schemaLocation=\"http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd\">

    <!-- Scans the classpath of this application for @Components to deploy as beans -->
    <context:component-scan base-package=\"springtest\" />

    <!-- Configures the @Controller programming model -->
    <mvc:annotation-driven />

    <bean class=\"org.springframework.web.servlet.view.InternalResourceViewResolver\">
        <property name=\"viewClass\" value=\"org.springframework.web.servlet.view.JstlView\"/>      
        <property name=\"prefix\" value=\"/WEB-INF/\"/>
        <property name=\"suffix\" value=\".jsp\"/>
        <property name=\"order\" value=\"1\"/>
    </bean>


    <bean id=\"parentDataSource\" class=\"org.apache.commons.dbcp.BasicDataSource\" abstract=\"true\">
        <property name=\"driverClassName\" value=\"com.mysql.jdbc.Driver\"/>        
        <property name=\"username\" value=\"\" />
        <property name=\"password\" value=\"\" />
        <property name=\"initialSize\" value=\"5\"/>
        <property name=\"validationQuery\" value=\"select 1\" />
        <property name=\"defaultAutoCommit\" value=\"false\" />
        <property name=\"maxActive\" value=\"100\" />
        <property name=\"maxIdle\" value=\"10\" />
        <property name=\"maxWait\" value=\"15000\" />
        <property name=\"removeAbandoned\" value=\"true\" />
        <property name=\"removeAbandonedTimeout\" value=\"300\" />
        <property name=\"testOnBorrow\" value=\"true\" />
    </bean> 


    <bean id=\"master\" parent=\"parentDataSource\">
        <property name=\"url\" value=\"jdbc:mysql://${db.host.master}/te_admin?autoReconnect=true\" />
    </bean> 

    <bean id=\"server1\" parent=\"parentDataSource\">
       <property name=\"url\" value=\"jdbc:mysql://${db.host.server1}/te_db?autoReconnect=true\"/>
    </bean>

    <bean id=\"server2\" parent=\"parentDataSource\">
       <property name=\"url\" value=\"jdbc:mysql://${db.host.server2}/te_db?autoReconnect=true\"/>
    </bean>


    <bean id=\"server3\" parent=\"parentDataSource\">
       <property name=\"url\" value=\"jdbc:mysql://${db.host.server3}/te_db?autoReconnect=true\"/>
    </bean> 

    <bean id=\"masterJdbcTemplate\" class=\"org.springframework.jdbc.core.JdbcTemplate\">
        <constructor-arg><ref bean=\"master\"/></constructor-arg>
    </bean>

    <bean id=\"testdao\" class=\"springtest.TestDAO\">
        <property name=\"dataSource\" ref=\"dataSource\"/>
    </bean>

    <bean id=\"dataSource\" class=\"springtest.RoutingDataSource\">
        <property name=\"targetDataSources\">
            <map>
                <entry key=\"server1\" value-ref=\"server1\"/>
                <entry key=\"server2\" value-ref=\"server2\"/>
                <entry key=\"server3\" value-ref=\"server3\"/>
            </map>
        </property>
        <property name=\"defaultTargetDataSource\" ref=\"server3\"/>
    </bean>


    <!--  properties file -->
    <context:property-placeholder location=\"classpath:local.properties\"/>

</beans>

这是错误

java.lang.NullPointerException
springtest.TestDAO.getDomains(TestDAO.java:15)

    

解决方法

那是因为您自己实例化了5，而不使用上下文中定义的bean。您需要将``5''bean注入到控制器中，例如

@Controller
@RequestMapping(value=\"/test\")
public class HandleRequest {

   private @Autowired TestDAO testDao;

   @RequestMapping(method=RequestMethod.GET)
   public String handle(Model model){    
      SessionContextHolder.setDBServer(\"server1\");
      List domains = testDAO.getDomains();
      model.addAttribute(\"domains\",domains);
      return \"test1\";
   }
}