问题描述
Stacktrace:org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:505)org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:416)org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)javax.servlet.http.HttpServlet.service(HttpServlet.java:717)root cause java.lang.NullPointerExceptionservlet.CountIPShw.doPost(CountIPShw.java:110)servlet.CountIPShw.doGet(CountIPShw.java:50)javax.servlet.http.HttpServlet.service(HttpServlet.java:617)javax.servlet.http.HttpServlet.service(HttpServlet.java:717)org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.java:968)org.apache.jsp.mng.ipcount_jsp._jspService(ipcount_jsp.java:90)org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)javax.servlet.http.HttpServlet.service(HttpServlet.java:717)org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:374)org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)javax.servlet.http.HttpServlet.service(HttpServlet.java:717)servlet.CountIPShw.doPost(CountIPShw.java:110)代码如下：ExecuteDB exedb = new ExecuteDB();ResultSet rs1 = exedb.exeQuery("select count(*) from ip where date != ""+date+"";");ResultSet rs2 = exedb.exeQuery("select * from visit;");ResultSet rs3 = exedb.exeQuery("select count(*) from ip where date = ""+date+"";");try {if(rs1.next()&&rs2.next()){//这是第110行if(rs1.getString(1)!=null&&!rs1.getString(1).equals("")){amount = rs1.getInt(1)+rs2.getInt(1);exedb.exeSql("update visit set amount = "+amount);exedb.exeSql("delete from ip where date != ""+date+"";");}}rs1.close();rs2.close();if(rs3.next()){if(rs3.getString(1)!=null&&!rs3.getString(1).equals(""))today = rs3.getInt(1);}rs3.close();} catch (SQLException e) {}exedb.close();这里的ExecuteDB 类代码如下：package newshop;import java.sql.*;public class ExecuteDB{private String userName="****";private String userPassword="****";private String url="jdbc:mysql://127.0.0.1:3306/****";private Connection dbConn;private Statement stmt;private ResultSet rs; private String errMes; public ExecuteDB(){dbConn = this.getConn();stmt = null;rs = null;this.errMes = this.getErrMes();} public Connection getConn() { try { Class.forName("org.gjt.mm.mysql.Driver").newInstance();dbConn= DriverManager.getConnection(url,userName,userPassword); } catch(Exception e) { dbConn = null; errMes=e.toString(); }finally{ } return dbConn; } public boolean exeSql(String strSql){boolean isSuc = false;try{ stmt=dbConn.createStatement();stmt.executeUpdate(strSql);isSuc = true; }catch(Exception e){this.errMes = this.errMes + "<br>" +e.toString();}finally{}return isSuc;} public ResultSet exeQuery(String strSql){try{ stmt=dbConn.createStatement();rs =stmt.executeQuery(strSql);}catch(Exception e){ this.errMes = this.errMes + "<br>" +e.toString();rs = null;}finally{}return rs;} public void close() { try { stmt.close(); dbConn.close(); } catch (SQLException e) { this.errMes = this.errMes + "<br>" +e.toString(); } } public String getErrMes() { return errMes; }} 问题补充：Stacktrace:org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:505)org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:416)org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)javax.servlet.http.HttpServlet.service(HttpServlet.java:717)root cause java.lang.NullPointerExceptionservlet.CountIPShw.doPost(CountIPShw.java:110)servlet.CountIPShw.doGet(CountIPShw.java:50)javax.servlet.http.HttpServlet.service(HttpServlet.java:617)javax.servlet.http.HttpServlet.service(HttpServlet.java:717)org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.java:968)org.apache.jsp.mng.ipcount_jsp._jspService(ipcount_jsp.java:90)org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)javax.servlet.http.HttpServlet.service(HttpServlet.java:717)org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:374)org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)javax.servlet.http.HttpServlet.service(HttpServlet.java:717)servlet.CountIPShw.doPost(CountIPShw.java:110)代码如下：ExecuteDB exedb = new ExecuteDB();ResultSet rs1 = exedb.exeQuery("select count(*) from ip where date != ""+date+"";");ResultSet rs2 = exedb.exeQuery("select * from visit;");ResultSet rs3 = exedb.exeQuery("select count(*) from ip where date = ""+date+"";");try {if(rs1.next()&&rs2.next()){//这是第110行if(rs1.getString(1)!=null&&!rs1.getString(1).equals("")){amount = rs1.getInt(1)+rs2.getInt(1);exedb.exeSql("update visit set amount = "+amount);exedb.exeSql("delete from ip where date != ""+date+"";");}}rs1.close();rs2.close();if(rs3.next()){if(rs3.getString(1)!=null&&!rs3.getString(1).equals(""))today = rs3.getInt(1);}rs3.close();} catch (SQLException e) {}exedb.close();这里的ExecuteDB 类代码如下：package newshop;import java.sql.*;public class ExecuteDB{private String userName="****";private String userPassword="****";private String url="jdbc:mysql://127.0.0.1:3306/****";private Connection dbConn;private Statement stmt;private ResultSet rs; private String errMes; public ExecuteDB(){dbConn = this.getConn();stmt = null;rs = null;this.errMes = this.getErrMes();} public Connection getConn() { try { Class.forName("org.gjt.mm.mysql.Driver").newInstance();dbConn= DriverManager.getConnection(url,userName,userPassword); } catch(Exception e) { dbConn = null; errMes=e.toString(); }finally{ } return dbConn; } public boolean exeSql(String strSql){boolean isSuc = false;try{ stmt=dbConn.createStatement();stmt.executeUpdate(strSql);isSuc = true; }catch(Exception e){this.errMes = this.errMes + "<br>" +e.toString();}finally{}return isSuc;} public ResultSet exeQuery(String strSql){try{ stmt=dbConn.createStatement();rs =stmt.executeQuery(strSql);}catch(Exception e){ this.errMes = this.errMes + "<br>" +e.toString();rs = null;}finally{}return rs;} public void close() { try { stmt.close(); dbConn.close(); } catch (SQLException e) { this.errMes = this.errMes + "<br>" +e.toString(); } } public String getErrMes() { return errMes; }}
解决方案
你是在程序中对于每个请求自己创建连接，当请求比较多的时候，连接就不够用了。而且，你在doPost()里面，当有异常的时候，也没有关闭数据库连接，只有正常结束的情况下才关闭。一般数据库连接都是有限制的，你这样自己创建连接肯定不行，当并发请求比较多的时候，数据库就会连接不上，那你执行sql的时候就肯定会出错了。你的代码还有一个很大的问题，java里面处理异常，你不能吞了它，而应该把它重新扔出来，最后在doPost之类的方法里面统一处理。在你的代码里，getConn() 方法，已经exeQuery()方法里面的异常你都只是记录，但是没有抛出来，这样，程序出错的时候是空指针，但是实际上错误是在一开始创建连接的时候。就会误导你debug。建议使用一些DAO框架，像iBatis、Hibernate之类的，可以提供数据库连接池。
解决方案二：
引用if(rs1.next()&&rs2.next()){//这是第110行 简单的看了一下代码，显然rs1或者rs2当中有一个为null.再看实现：public ResultSet exeQuery(String strSql){try{ stmt=dbConn.createStatement(); rs =stmt.executeQuery(strSql);}catch(Exception e){ this.errMes = this.errMes + "<br>" +e.toString(); rs = null;}finally{}return rs;} 这里rs不能是共享成员变量应该改为：public ResultSet exeQuery(String strSql){ ResultSet rset = null;try{ stmt=dbConn.createStatement(); rset =stmt.executeQuery(strSql);}catch(Exception e){ this.errMes = this.errMes + "<br>" +e.toString();}finally{}return rset;}再把if(rs1.next()&&rs2.next())判断条件多加两个if (rs1!=null && rs1.next() && rs2!=null && rs2.next())这样才有效果。
解决方案三：
睡觉 了,明天 有时间 再看了
解决方案四：
而且你这代码里在RS.NEXT偱环里还有exedb.exeSql("update visit set amount = "+amount); 这些操作在这些操作里STMT又重新赋值产生了变化 ,也就有可能导致RS变空感觉这代码有点乱.....
解决方案五：
你把这个public ResultSet exeQuery(String strSql) {try { stmt=dbConn.createStatement(); rs =stmt.executeQuery(strSql);} catch(Exception e) { this.errMes = this.errMes + "<br>" +e.toString();rs = null; }finally{ } return rs; } 改成public ResultSet exeQuery(String strSql) {try { stmt=dbConn.createStatement(); return stmt.executeQuery(strSql);} catch(Exception e) { this.errMes = this.errMes + "<br>" +e.toString();}finally{ } } 不要把查询结果赋给RS再返回了,这样的话你的三个RS就变成同一个了,直接把结果 返回
解决方案六：
你把刚才 改的代码再替回来吧,可能我记错了,那样初始化也不可以(不过你这样取数据库连接还是会造成混乱,链接也有可能没法及时释放 等 问题)ExecuteDB exedb = new ExecuteDB(); ResultSet rs1 = exedb.exeQuery("select count(*) from ip where date != ""+date+"";"); ResultSet rs2 = exedb.exeQuery("select * from visit;"); ResultSet rs3 = exedb.exeQuery("select count(*) from ip where date = ""+date+"";"); 这段代码三个RS感觉是同一个,因为你只声明了一个exedb
解决方案七：
你能断点调试看看是改后的哪一行出错吗?
解决方案八：
这个就得对JAVA对像初始化的执行顺序 要有一定的了解了
解决方案九：
你先试一下看看结果
解决方案十：
但是这样也不合适,将来数据库链接会不及时释放
解决方案十一：
代码 初始化的时候 不能这样写吧dbConn = this.getConn(); 你试一下把public ExecuteDB() { dbConn = this.getConn(); stmt = null; rs = null;this.errMes = this.getErrMes();} 改成public ExecuteDB() { try { Class.forName("org.gjt.mm.mysql.Driver").newInstance(); dbConn= DriverManager.getConnection(url,userName,userPassword); } catch(Exception e) { dbConn = null; errMes=e.toString(); }finally{ } stmt = null; rs = null}
解决方案十二：
servlet.CountIPShw.doPost(CountIPShw.java:110)代码如下： 这里提示的110行是哪一行