为什么当我提供了数据库 URL 时,它会显示 null URL 并在异常中给出一个空的 ' ' 类?
我在使用 Tomcat 时尝试通过 servlet 连接到 derby 数据库。当 servlet 运行时,我得到以下异常:
org.apache.tomcat.dbcp.dbcp.SQLNestedException: Cannot create JDBC driver of class '' for connect URL 'null'
at org.apache.tomcat.dbcp.dbcp.BasicDataSource.createConnectionFactory(BasicDataSource.java:1452)
at org.apache.tomcat.dbcp.dbcp.BasicDataSource.createDataSource(BasicDataSource.java:1371)
at org.apache.tomcat.dbcp.dbcp.BasicDataSource.getConnection(BasicDataSource.java:1044)
at servlets.servlet_1.doGet(servlet_1.java:23) // ---> Marked the statement in servlet
at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:224)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:169)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:929)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:405)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:964)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:515)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:302)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.NullPointerException
at sun.jdbc.odbc.JdbcOdbcDriver.getProtocol(JdbcOdbcDriver.java:507)
at sun.jdbc.odbc.JdbcOdbcDriver.knownURL(JdbcOdbcDriver.java:476)
at sun.jdbc.odbc.JdbcOdbcDriver.acceptsURL(JdbcOdbcDriver.java:307)
at java.sql.DriverManager.getDriver(DriverManager.java:253)
at org.apache.tomcat.dbcp.dbcp.BasicDataSource.createConnectionFactory(BasicDataSource.java:1437)
... 24 more
Servlet:
package servlets;
import java.io.IOException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.servlet.http.*;
import javax.servlet.*;
import javax.sql.DataSource;
public class servlet_1 extends HttpServlet {
@Override
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
try {
// String queryString = request.getQueryString();
System.out.println("!!!!!!!!!!!!!!!!!!!");
Context initContext = new InitialContext();
Context envContext = (Context)initContext.lookup("java:comp/env");
DataSource ds = (DataSource)envContext.lookup("jdbc/PollDatasource");
Connection connection = ds.getConnection(); // -->LINE 23
String sqlQuery = "select * from PollResult";
PreparedStatement statement = connection.prepareStatement(sqlQuery);
ResultSet set = statement.executeQuery();
System.out.println("after the final statement");
} catch (Exception exc) {
exc.printStackTrace();
}
}
}
这是什么异常?为什么会出现此异常?
我在Tomcat的context.xml
中添加了如下标签:
<Resource name="jdbc/PollDatasource" auth="Container" type="javax.sql.DataSource"
driverClassName="org.apache.derby.jdbc.EmbeddedDriver"
url="jdbc:derby://localhost:1527/poll_database;create=true"
username="suhail" password="suhail"
maxActive="20" maxIdle="10" maxWait="-1" />
这在 web.xml
中:
<resource-ref>
<description>my connection</description>
<res-ref-name>jdbc/PollDatasource</res-ref-name>
<res-type>javax.sql.DataSource</res-type>
<res-auth>Container</res-auth>
</resource-ref>
我在哪里做错了?
显示数据库 URL 的图像..
注意:在@Bryan Pendleton 回答之后,我将驱动程序更改为 org.apache.derby.jdbc.ClientDriver
但我得到了同样的异常。
最佳答案
我看不出有什么明显错误,但也许另一种方法可以帮助您调试它?
您可以尝试在每个应用程序上下文中指定您的数据源,而不是在全局 tomcat 中指定。
您可以通过创建 src/main/webapp/META-INF/context.xml 来做到这一点(我假设您使用的是标准 maven 目录结构 - 如果不是,那么 META-INF 文件夹应该是WEB-INF 目录的同级)。 META-INF/context.xml 文件的内容类似于:
<?xml version="1.0" encoding="UTF-8"?>
<Context [optional other attributes as required]>
<Resource name="jdbc/PollDatasource" auth="Container"
type="javax.sql.DataSource" driverClassName="org.apache.derby.jdbc.ClientDriver"
url="jdbc:derby://localhost:1527/poll_database;create=true"
username="suhail" password="suhail" maxActive="20" maxIdle="10" maxWait="-1"/>
</Context>
显然路径和 docBase 需要与您的应用程序的具体细节相匹配。
使用这种方法,您不必在 Tomcat 的 context.xml 文件中指定数据源详细信息。不过,如果您有多个应用程序与同一个数据库通信,那么您的方法更有意义。
无论如何,试一试,看看是否有什么不同。它可能会为我们提供有关您的方法出了什么问题的线索。
关于java - 无法为连接 URL ' ' : I do not understand this exception 创建类 'null' 的 JDBC 驱动程序,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/11516747/