web 项目连接mysql报NullPointerException问题
2014-08-03 17:15
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这个是我的出错信息
出现空指针错误,后台报错信息为
这是我的DBManager代码
在实例化statement中createStatement出现了错误,无法进行实例化。出现包未找到
解决方法:
注意将mysql 的jdbc包放在web-inf的lib包中,要将其进行编译
有可能你修改了某一段的jdbc操作代码,tomcat没有反应过来,即不能再实例化,这个时候需要将tomcat服务器重启
java.lang.NullPointerException com.implement.DBManager.getResultSet(DBManager.java:50) com.implement.HelloWorld.getMessage(HelloWorld.java:72) com.implement.HelloWorld.doGet(HelloWorld.java:45) javax.servlet.http.HttpServlet.service(HttpServlet.java:620) javax.servlet.http.HttpServlet.service(HttpServlet.java:727) org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
出现空指针错误,后台报错信息为
java.lang.NullPointerException at com.implement.DBManager.getResultSet(DBManager.java:50) at com.implement.HelloWorld.getMessage(HelloWorld.java:72) at com.implement.HelloWorld.doGet(HelloWorld.java:45) at javax.servlet.http.HttpServlet.service(HttpServlet.java:620) at javax.servlet.http.HttpServlet.service(HttpServlet.java:727) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1040) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607) at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2442) at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:2431) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Unknown Source)
这是我的DBManager代码
package com.implement; import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; /** * Connection con = DBManager.getConnection(); * Statement statement = DBManager.getStatement(); * ResultSet resultSet = DBManager.getResultSet(statement, sql); * 这些一定要写,否则就可能会出错! * @author yj0416 * */ public class DBManager { private static final String DBDRIVER = "com.mysql.jdbc.Driver"; private static final String DBURL = "jdbc:mysql://localhost:3306/"; private static final String DATABASE = "test"; private static Connection con; public static Connection getConnection() { if (con == null) { try { Class.forName(DBDRIVER); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } try { con = DriverManager.getConnection(DBURL + DATABASE, "root", "541418452"); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } } return con; } public static Statement getStatement() { if (con == null) { getConnection(); } try { return con.createStatement(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); return null; } } public static ResultSet getResultSet(Statement statement, String sqlString) { ResultSet resultSet = null; try { resultSet = statement.executeQuery(sqlString); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } return resultSet; } public static ResultSet getResultSet(String sqlString) { Statement statement = DBManager.getStatement(); return DBManager.getResultSet(statement, sqlString); } public static void close(Statement statement) { try { statement.close(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public static void close(Connection connection) { try { connection.close(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public static void close(ResultSet resultSet) { try { resultSet.close(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } } }
在实例化statement中createStatement出现了错误,无法进行实例化。出现包未找到
解决方法:
注意将mysql 的jdbc包放在web-inf的lib包中,要将其进行编译
有可能你修改了某一段的jdbc操作代码,tomcat没有反应过来,即不能再实例化,这个时候需要将tomcat服务器重启
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