为何 stmt = conn.createStatement();老是异常抛出，怪事？

下面是有问题的源代码：
import  ...
public class test {
Connection conn;
public Vector getDataKenl(String sql) {
Vector father = new Vector();
Vector vecDate = new Vector();
ResultSet sres = null;
Statement stmt;
Boolean opStatus = new Boolean(true);
try{
//////////////////////////////////////////
//有问题的语句
            stmt = conn.createStatement();
/////////////////////////////////////////
sql = new String(sql.getBytes(),"ISO-8859-1");
          sres = stmt.executeQuery(sql);
vecDate = resultToVector(sres);
sres.close();
stmt.close();
father.addElement(opStatus);
father.addElement(vecDate); } catch (SQLException ex) {
opStatus = Boolean.valueOf("false");
father.addElement(opStatus); father.addElement(Integer.toString(ex.getErrorCode())); System.out.println(ex.toString());
}catch (UnsupportedEncodingException e) {
System.out.println(e.toString());
}
return father;
  }
}

你没有连数据库,conn是空,
应该先连接数据库再用stmt = conn.createStatement();

链了数据库，但是还是出错import  ...
public class test {
Connection conn;
public Vector getDataKenl(String sql) {
Vector father = new Vector();
Vector vecDate = new Vector();
ResultSet sres = null;
Statement stmt;
Boolean opStatus = new Boolean(true);
                  //连接数据库后，conn 为空值
                  conn = DbConnectionPool.getAConnection();
try{
//////////////////////////////////////////
//有问题的语句
            stmt = conn.createStatement();
/////////////////////////////////////////
sql = new String(sql.getBytes(),"ISO-8859-1");
          sres = stmt.executeQuery(sql);
vecDate = resultToVector(sres);
sres.close();
stmt.close();
father.addElement(opStatus);
father.addElement(vecDate); } catch (SQLException ex) {
opStatus = Boolean.valueOf("false");
father.addElement(opStatus); father.addElement(Integer.toString(ex.getErrorCode())); System.out.println(ex.toString());
}catch (UnsupportedEncodingException e) {
System.out.println(e.toString());
}
return father;
  }
}

连接数据库的可能就有问题,conn是空值就是没有连正确.

你在DataBase Pilot配数据库驱动程序没有？

判断一下conn是否是null吧。
另：把错误信息也贴出来

根本错误-1: nulljava.lang.NullPointerException
java.lang.Throwable()
java.lang.Exception()
java.lang.RuntimeException()
java.lang.NullPointerException()
java.util.Vector com.cbe.base.DBQuery.getDataKenl(java.lang.String)
java.util.Vector com.cbe.base.DBQuery.getDataKenl(java.lang.String)
java.util.Vector com.cbe.base.DBQuery.getData(java.lang.String)
void upgrade.ROOT._login_xjsp._jspService(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
void com.sun.jsp.runtime.HttpJspBase.service(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
void javax.servlet.http.HttpServlet.service(javax.servlet.ServletRequest, javax.servlet.ServletResponse)
void com.sun.jsp.runtime.JspServlet$JspServletWrapper.service(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
void com.ibm.ivj.jsp.runtime.JspDebugServlet.serviceJspFile(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse, java.lang.String, java.lang.Throwable)
void com.sun.jsp.runtime.JspServlet.service(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
void javax.servlet.http.HttpServlet.service(javax.servlet.ServletRequest, javax.servlet.ServletResponse)
void com.ibm.servlet.engine.webapp.StrictServletInstance.doService(javax.servlet.ServletRequest, javax.servlet.ServletResponse)
void com.ibm.servlet.engine.webapp.StrictLifecycleServlet._service(javax.servlet.ServletRequest, javax.servlet.ServletResponse)
void com.ibm.servlet.engine.webapp.IdleServletState.service(com.ibm.servlet.engine.webapp.StrictLifecycleServlet, javax.servlet.ServletRequest, javax.servlet.ServletResponse)
void com.ibm.servlet.engine.webapp.StrictLifecycleServlet.service(javax.servlet.ServletRequest, javax.servlet.ServletResponse)
void com.ibm.servlet.engine.webapp.ServletInstance.service(javax.servlet.ServletRequest, javax.servlet.ServletResponse, com.ibm.servlet.engine.webapp.WebAppServletInvocationEvent)
void com.ibm.servlet.engine.webapp.ValidServletReferenceState.dispatch(com.ibm.servlet.engine.webapp.ServletInstanceReference, javax.servlet.ServletRequest, javax.servlet.ServletResponse, com.ibm.servlet.engine.webapp.WebAppServletInvocationEvent)
void com.ibm.servlet.engine.webapp.ServletInstanceReference.dispatch(javax.servlet.ServletRequest, javax.servlet.ServletResponse, com.ibm.servlet.engine.webapp.WebAppServletInvocationEvent)
void com.ibm.servlet.engine.webapp.WebAppRequestDispatcher.handleWebAppDispatch(com.ibm.servlet.engine.webapp.WebAppRequest, javax.servlet.http.HttpServletResponse, boolean)
void com.ibm.servlet.engine.webapp.WebAppRequestDispatcher.dispatch(javax.servlet.ServletRequest, javax.servlet.ServletResponse, boolean)
void com.ibm.servlet.engine.webapp.WebAppRequestDispatcher.forward(javax.servlet.ServletRequest, javax.servlet.ServletResponse)
void com.ibm.servlet.engine.srt.WebAppInvoker.handleInvocationHook(java.lang.Object)
void com.ibm.servlet.engine.invocation.CachedInvocation.handleInvocation(java.lang.Object)
void com.ibm.servlet.engine.srp.ServletRequestProcessor.dispatchByURI(java.lang.String, com.ibm.servlet.engine.srp.ISRPConnection)
void com.ibm.servlet.engine.oselistener.OSEListenerDispatcher.service(com.ibm.servlet.engine.oselistener.api.IOSEConnection)
void com.ibm.servlet.engine.http_transport.HttpTransportHandler.handleConnection(java.net.Socket)
void com.ibm.servlet.engine.http_transport.HttpTransportHandler.run()
void java.lang.Thread.run()

java.lang.NullPointerException
java.lang.Throwable()
java.lang.Exception()
java.lang.RuntimeException()
java.lang.NullPointerException()
java.util.Vector com.cbe.base.DBQuery.getDataKenl(java.lang.String)
java.util.Vector com.cbe.base.DBQuery.getDataKenl(java.lang.String)
java.util.Vector com.cbe.base.DBQuery.getData(java.lang.String)

将conn定义成类的成员变量是不合适的, 最好定义在方法中，最后用完后在finally中将它关闭。

DbConnectionPool.getAConnection()
这个能不能连到数据库呢？你有没有测试过。

Connection conn=DriverManager.getConnection(sConnStr);
我这里SConnStr是数据库源，例如
String sConnStr="jdbc:odbc:xing";你只是创建Connection对象，但不赋值怎么行

调试易

为何 stmt = conn.createStatement();老是异常抛出，怪事？

解决方案 »