获取数据库连接出错了 conn = dbconn.getConnection(); 那就去你的DbCon 类啊!为什么他没有返回Connection 而是 null 解决方案 » 免费领取超大流量手机卡,每月29元包185G流量+100分钟通话, 中国电信官方发货 先谢谢你啊!我更正一下我的问题:package org.mmxbb.exam.util;import java.sql.Connection;import java.sql.DriverManager;import javax.naming.Context;import javax.naming.InitialContext;import javax.sql.DataSource;public class DBConn { DataSource ds = null; Connection conn = null; public DBConn() { } /** * <li>get the connection from lookup DataSource * @return Connection */ public Connection getConnection() { try {// Context initCtx = new InitialContext();// Context envCtx = (Context)initCtx.lookup("java:comp/env");// ds = (DataSource)envCtx.lookup("jdbc/exam");// conn=ds.getConnection(); Connection conn = null; Class.forName("com.mysql.jdbc.Driver"); conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/exam","root","123"); } catch (Exception e) { System.err.println("getConnection error: " + e); return null; } return conn; } /** * return connection to pool */ public void close() { try { conn.close(); } catch (Exception e) { e.printStackTrace(); } }}package org.mmxbb.exam.dao; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; import java.util.ArrayList; import java.util.Collection; import org.mmxbb.exam.bean.Examinee; import org.mmxbb.exam.business.LogonForm; import org.mmxbb.exam.business.examinee.ExamineeActionForm; import org.mmxbb.exam.business.program.RandomDistributeExamPaperForm; import org.mmxbb.exam.util.DBConn; public class ExamineeDAO { DBConn dbconn = null; private Connection conn = null; private int rowCount; private int pageCount; private int length; private String pagestr; private String conditionStr = ""; private static final String IS_USER = "SELECT password FROM EX_EXAMINEE WHERE examinee_id = ?"; private static final String FIND_BY_KEY = "SELECT * FROM EX_EXAMINEE WHERE examinee_id = ?"; /** * get a connection from a DB pool * @return Connection */ public ExamineeDAO() { try { dbconn = new DBConn(); System.out.println("---------ExamineeDAO() -----------------------------------"); conn = dbconn.getConnection(); System.out.println("---------ExamineeDAO() ----已获得数据库的连接了--------------------"+conn);} catch (Exception ex) { ex.printStackTrace(); } } public boolean isUser(LogonForm logonForm) { PreparedStatement pstmt = null; ResultSet rs = null; boolean isUser = false; try { System.out.println("-----ExamineeDAO.java---isUser()--------------"+conn); pstmt = conn.prepareStatement(IS_USER); pstmt.setString(1, logonForm.getUserName()); rs = pstmt.executeQuery(); if (rs.next()) { if (rs.getString(1).equals(logonForm.getPassword())) { isUser = true; } } } catch (SQLException ex) { ex.printStackTrace(); } finally { try { rs.close(); rs = null; pstmt.close(); pstmt = null; conn.close(); conn = null; } catch (SQLException ex1) { ex1.printStackTrace(); } } return isUser; } } tomcat 控制台出现以下信息: 信息: Initializing, config='org.apache.struts.taglib.html.LocalStrings', returnNull=true---------ExamineeDAO() --------------------------------------------ExamineeDAO() ----已获得数据库的连接了-------------------------------null-----ExamineeDAO.java---isUser()--------------null请问为什么我得不到connection?得到却是null 如果数据连接的代码有误,要查看是不是你所用的桥架不对呀,那就是IDE的DB conn 工具啦,myeclipse 用DB browser啦,jbuilder 也有可视化连接验证的界面啦, 问题已找到,谢谢大家.DBConn() 里有错误. 部署Web应用出现的错误,求指教!!! hibernate查询 ssh框架整合问题 if标签简单问题 通过JAVA读取通过MQ资源管理器放入的测试消息报错 急。。。。。。。。在线等啊?? 从今天开始我要以一个科学家的心态那样面对计算机 有人搞没搞过apache协同多个tomcat,实现动载平衡,跪求!!!!!!!急。。。。 怎样在JB7下配置WEBLOGIC 7 特大喜讯:JSP+数据库的免费空间+xml+WAP,FREE!!! 求一个好的方法 邮件代码出错
import java.sql.Connection;
import java.sql.DriverManager;import javax.naming.Context;
import javax.naming.InitialContext;
import javax.sql.DataSource;public class DBConn {
DataSource ds = null;
Connection conn = null; public DBConn() {
} /**
* <li>get the connection from lookup DataSource
* @return Connection
*/
public Connection getConnection() {
try {
// Context initCtx = new InitialContext();
// Context envCtx = (Context)initCtx.lookup("java:comp/env");
// ds = (DataSource)envCtx.lookup("jdbc/exam");
// conn=ds.getConnection(); Connection conn = null;
Class.forName("com.mysql.jdbc.Driver");
conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/exam","root","123");
} catch (Exception e) {
System.err.println("getConnection error: " + e);
return null;
}
return conn;
}
/**
* return connection to pool
*/
public void close() {
try {
conn.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
package org.mmxbb.exam.dao;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.Collection; import org.mmxbb.exam.bean.Examinee;
import org.mmxbb.exam.business.LogonForm;
import org.mmxbb.exam.business.examinee.ExamineeActionForm;
import org.mmxbb.exam.business.program.RandomDistributeExamPaperForm;
import org.mmxbb.exam.util.DBConn;
public class ExamineeDAO {
DBConn dbconn = null;
private Connection conn = null; private int rowCount;
private int pageCount;
private int length;
private String pagestr;
private String conditionStr = "";
private static final String IS_USER =
"SELECT password FROM EX_EXAMINEE WHERE examinee_id = ?";
private static final String FIND_BY_KEY =
"SELECT * FROM EX_EXAMINEE WHERE examinee_id = ?";
/**
* get a connection from a DB pool
* @return Connection
*/
public ExamineeDAO() {
try {
dbconn = new DBConn();
System.out.println("---------ExamineeDAO() -----------------------------------");
conn = dbconn.getConnection();
System.out.println("---------ExamineeDAO() ----已获得数据库的连接了--------------------"+conn);
} catch (Exception ex) {
ex.printStackTrace();
}
} public boolean isUser(LogonForm logonForm) {
PreparedStatement pstmt = null;
ResultSet rs = null;
boolean isUser = false; try {
System.out.println("-----ExamineeDAO.java---isUser()--------------"+conn);
pstmt = conn.prepareStatement(IS_USER);
pstmt.setString(1, logonForm.getUserName());
rs = pstmt.executeQuery();
if (rs.next()) {
if (rs.getString(1).equals(logonForm.getPassword())) {
isUser = true;
}
}
} catch (SQLException ex) {
ex.printStackTrace();
} finally {
try {
rs.close();
rs = null;
pstmt.close();
pstmt = null;
conn.close();
conn = null;
} catch (SQLException ex1) {
ex1.printStackTrace();
}
}
return isUser;
}
}
tomcat 控制台出现以下信息: 信息: Initializing, config='org.apache.struts.taglib.html.LocalStrings', returnNull=true
---------ExamineeDAO() -----------------------------------
---------ExamineeDAO() ----已获得数据库的连接了-------------------------------null-----ExamineeDAO.java---isUser()--------------null
请问为什么我得不到connection?得到却是null