我正在学习为我的Web应用程序设置数据库连接，并且遇到了this链接。我使用TomCat跟踪它的示例，并使用我的数据库信息配置conf / Server.xml。这是我的Conf / server.xml文件 -
<Resource name="jdbc/MyMagnumFt"
global="jdbc/MyMagnumFt"
auth="Container"
type="javax.sql.DataSource"
driverClassName="oracle.jdbc.driver.OracleDriver"
url="jdbc:oracle:thin:@<<myCorrectURL>>"
username="user"
password="pass"
maxActive="100"
maxIdle="20"
minIdle="5"
maxWait="10000"/>
上面链接中的示例要求在context.xml文件中创建ResourceLink。所以我在conf / context.xml文件中创建了一个ResourceLink -
<ResourceLink name="jdbc/MyLocalMagnumFt"
global="jdbc/MyMagnumFt"
auth="Container"
type="javax.sql.DataSource" />
现在，此示例未指定有关在web.xml文件中进行更改的任何内容。所以我没有为此烦恼。
这是我试图获得连接的servlet代码 -
public class ResourcePool extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
InitialContext ctx = null;
Connection con = null;
Statement stmt = null;
ResultSet rs = null;
try{
ctx = new InitialContext();
DataSource ds = (DataSource) ctx.lookup("java:/comp/env/jdbc/MyLocalMagnumFt");
con = ds.getConnection();
stmt = con.createStatement();
rs = stmt.executeQuery("select empid, name from Employee");
lookup（）工作文件并获取我在server.xml中编码的数据源信息。但是，当控制转到getConnection（）语句时，它退出try块并进入finally块的rs.close（）语句。在控制台中我看到以下错误 -
May 15, 2017 4:27:46 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [ResourcePool] in context with path [/myJNDI2] threw exception
java.lang.NullPointerException
at org.ashu.tester.ResourcePool.doGet(ResourcePool.java:65)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:474)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:624)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:349)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:783)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:798)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1434)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
现在我探讨了不同的帖子，将数据源配置为在Application的context.xml中设置数据库信息并在web.xml中创建一个条目，但我想试试这个例子并设置一个全局数据源应用程序可以使用。
如果我在这里遗漏了某些内容或者您需要更多详细信息，请告知我们。这是我的项目设置的屏幕截图 - Project Setup
这是完整的代码 -
package org.ashu.tester;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.DataSource;
public class ResourcePool extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
InitialContext ctx = null;
Connection con = null;
Statement stmt = null;
ResultSet rs = null;
try{
ctx = new InitialContext();
DataSource ds = (DataSource) ctx.lookup("java:/comp/env/jdbc/MyLocalMagnumFt");
con = ds.getConnection();
stmt = con.createStatement();
rs = stmt.executeQuery("select empid, name from Employee");
PrintWriter out = response.getWriter();
response.setContentType("text/html");
out.print("<html><body><h2>Employee Details</h2>");
out.print("<table border=\"1\" cellspacing=10 cellpadding=5>");
out.print("<th>Employee ID</th>");
out.print("<th>Employee Name</th>");
while(rs.next())
{
out.print("<tr>");
out.print("<td>" + rs.getInt("empid") + "</td>");
out.print("<td>" + rs.getString("name") + "</td>");
out.print("</tr>");
}
out.print("</table></body><br/>");
//lets print some DB information
out.print("<h3>Database Details</h3>");
out.print("Database Product: "+con.getMetaData().getDatabaseProductName()+"<br/>");
out.print("Database Driver: "+con.getMetaData().getDriverName());
out.print("</html>");
}catch(NamingException e){
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}finally{
try {
rs.close();
stmt.close();
con.close();
ctx.close();
} catch (SQLException e) {
System.out.println("Exception in closing DB resources");
} catch (NamingException e) {
System.out.println("Exception in closing Context");
}
}
}
}