搞了好久了.头都大了.各位帮帮忙吧.该怎么解决

搞了好久了.头都大了.各位帮帮忙吧.
错误:
2012-4-6 19:51:07 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
at mybean.StyleList.getBuffer(StyleList.java:36)
at org.apache.jsp.index_jsp._jspService(index_jsp.java:127)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:374)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
at org.apache.coyote.ajp.AjpAprProcessor.process(AjpAprProcessor.java:427)
at org.apache.coyote.ajp.AjpAprProtocol$AjpConnectionHandler.process(AjpAprProtocol.java:384)
at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1527)
at java.lang.Thread.run(Thread.java:619)
styleList.java:

Java code

/* * 网站JAVABEAN * 所有帖子分类列表. * 使用数据源连接. * 前后台共用JAVABEAN. */package mybean;import java.sql.*;import mybean.DBConnSource;public class StyleList {    private String tableName;    private Statement stmt;    private ResultSet rs;    private DBConnSource dbc;         public StyleList(){}        public void setTableName(String n){        this.tableName=n;    }        public StringBuffer getBuffer(){        StringBuffer buffer=new StringBuffer();        dbc=new DBConnSource("jdbc/myweb");           try{                        stmt=dbc.getStmt();             }catch(Exception e){                        System.out.print("不能连接到数据源"+e.toString());            }                      try{    //这就是36行;             String strSql="SELECT * FROM "+tableName;              rs = stmt.executeQuery(strSql);                          while(rs.next()){                                    buffer.append("<a href='style.jsp?style="+rs.getString("style")+"' target=_blank>"+rs.getString("style")+"</a>");                buffer.append("&nbsp;&nbsp;&nbsp;");                }                       }catch(SQLException e){            System.out.print("结果集rs获取出错"+e.toString());        }finally{             try{               //关闭 ResultSet rs.                     if(rs!=null){                      rs.close();                     }                 }catch(SQLException ex){                      System.out.print("关闭rs出错"+ex.toString());                 }finally{                         try{               // 关闭 Statement stmt.                                 if(stmt!=null){                                stmt.close();                              }                              }catch(SQLException ex){                                System.out.print("关闭stmt出错"+ex.toString());                              }                  }             dbc.DBclose();  //关闭 DBConnsource dbc;                }         return buffer;    }} 
 

谢谢!

[解决办法]
java.lang.NullPointerException
at mybean.StyleList.getBuffer(StyleList.java:36)

估计你36行算错了吧？应该是stmt == null 吧。

你是不是没注意之前已经出错误信息了？？
System.out.print("不能连接到数据源"+e.toString());
这行字没看到输出么？

[解决办法]
//帮你修改了一下。

Java code

import java.sql.Connection;import java.sql.PreparedStatement;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.sql.DataSource;public class DBConnSource{    public static Connection getConnection(String dsName){        Connection conn = null;            Context initCtx;            try {                initCtx = new InitialContext();                Context ctx =(Context)initCtx.lookup("java:comp/env");                DataSource ds =(DataSource)ctx.lookup(dsName);                conn = ds.getConnection();            } catch (NamingException e) {                e.printStackTrace();            } catch (SQLException e) {                e.printStackTrace();            }        return conn;    }       public static Statement getStmt(Connection conn){        Statement stmt = null;        try {            stmt=conn.createStatement();        } catch (SQLException e) {            e.printStackTrace();        }        return stmt;    }        public static PreparedStatement getPstmt(Connection conn,String sql){        PreparedStatement pstmt = null;        try {            pstmt=conn.prepareStatement(sql);        } catch (SQLException e) {            e.printStackTrace();        }        return pstmt;    }        public static void close(Statement stmt){        if(stmt!=null){            try {                stmt.close();            } catch (SQLException e) {                e.printStackTrace();            }        }    }    public static void close(PreparedStatement pstmt){        if(pstmt!=null){            try {                pstmt.close();            } catch (SQLException e) {                e.printStackTrace();            }        }    }    public static void close(Connection conn){        if(conn!=null){            try {                conn.close();            } catch (SQLException e) {                e.printStackTrace();            }        }    }    public static void close(ResultSet rs){        if(rs!=null){            try {                rs.close();            } catch (SQLException e) {                e.printStackTrace();            }        }    }} 

 

查看更多 下一篇