无法通过Spring加载数据库驱动程序，但可以在类路径上手动找到它

Question

I'm getting a ClassNotFoundException on a database driver class when attempting to create a data source using Spring running under Tomcat. I am, however, able to load the driver class directly from the same data access component (both via Class.forName and getClass().getClassLoader().loadClass() ). The driver jar is only installed in one place ( $CATALINA_HOME/lib ).

The data source definition in the Spring config file:

<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource">
    <property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
    <property name="url" value="${jdbc.url}"/>
    <property name="username" value="${jdbc.username}"/>
    <property name="password" value="${jdbc.password}"/>
</bean>

The DAO definition in the Spring config file:

<bean id="countryDao" class="com.mycompany.pmo.dao.CountryDao">
    <constructor-arg ref="dataSource"/>
</bean>

The DAO itself:

public class CountryDao {
    private NamedParameterJdbcTemplate jdbcTemplate;

    public CountryDao(DataSource dataSource) {
        jdbcTemplate = new NamedParameterJdbcTemplate(dataSource);
    }

    public List<Country> getCountries() {
        //I can manually load the driver class here
        String sql = "select * from ref.country";

        Map<String, Object> namedParameters = new HashMap<String, Object>();
        //next line is line 34, where the stack trace starts
        return jdbcTemplate.query(sql, namedParameters,new CountryMapper());
    }
}

The stack trace:

Feb 20, 2013 2:18:35 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [appServlet] in context with path [/PMO] threw exception [Request processing failed; nested exception is org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is org.apache.commons.dbcp.SQLNestedException: Cannot load JDBC driver class '"com.microsoft.sqlserver.jdbc.SQLServerDriver"'] with root cause
java.lang.ClassNotFoundException: "com.microsoft.sqlserver.jdbc.SQLServerDriver"
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1714)
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1559)
    at org.apache.commons.dbcp.BasicDataSource.createConnectionFactory(BasicDataSource.java:1420)
    at org.apache.commons.dbcp.BasicDataSource.createDataSource(BasicDataSource.java:1371)
    at org.apache.commons.dbcp.BasicDataSource.getConnection(BasicDataSource.java:1044)
    at org.springframework.jdbc.datasource.DataSourceUtils.doGetConnection(DataSourceUtils.java:111)
    at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:77)
    at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:573)
    at org.springframework.jdbc.core.JdbcTemplate.query(JdbcTemplate.java:637)
    at org.springframework.jdbc.core.JdbcTemplate.query(JdbcTemplate.java:662)
    at org.springframework.jdbc.core.JdbcTemplate.query(JdbcTemplate.java:702)
    at org.springframework.jdbc.core.namedparam.NamedParameterJdbcTemplate.query(NamedParameterJdbcTemplate.java:166)
    at org.springframework.jdbc.core.namedparam.NamedParameterJdbcTemplate.query(NamedParameterJdbcTemplate.java:172)
    at com.mycompany.pmo.dao.CountryDao.getCountries(CountryDao.java:34)

Answer 1

The jar should not be in $CATALINA_HOME/lib . It should be in WEB-INF/lib of your web app. I believe $CATALINA_HOME/lib will be used to load and run Tomcat , but your app classpath dependencies are loaded from WEB-INF/lib .

If you are developing in an IDE and running your program in it, you might also have to add the jar to your project build path.

Answer 2

As @Sotirios Delimanolis mentioned (+1) try to put the jar under WEB-INF/lib of your application.

The fact that the class is found using your manual code and cannot be found via Spring signals that the problem is in class loader. When you call Class.forName() you are definitely using the system class loader, so the class is loaded from catalina lib directory. I cannot explain why it works when you are calling getClass().getClassLoader().loadClass() from you DAO: it in this case the same application class loader should be used. But probably I do not know deeply enough how does Spring itself play with class loaders.