数组越界了
比如
String[] s = {"1","2","3","4","5"};
System.out.println(s[5]);

这样就错了，编译能通过，但运行时会异常

贴代码！·
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数组越界

超过了字符串的长度了吧。

for(int i=0; i<messages.length; i++) 
      {
        int InboxID=i+InboxMsgTotalNum+1;   //要存储的邮件在INBOX的位置
         javax.mail.Address[] addr=messages[i].getFrom();
         String senderAddr=new String();
         senderAddr=addr[0].toString();
         senderAddr.trim();
         int start=senderAddr.indexOf("<");      
          int end=senderAddr.indexOf(">");
         String  sender=new String();
         sender=senderAddr.substring(start+1, end);  // 获得发送者地址
         
         String subject=new String();
         subject=messages[i].getSubject();  
         
          Object MsgContent = messages[i].getContent();  
          MsgContent = messages[i].getContent();   //怎样存储到数据库中？？？？？
                      //邮件的内容出错：javax.mail.internet.MimeMultipart@4d2197 

         java.text.Format formatter = new java.text.SimpleDateFormat("yyyy-MM-dd hh:mm")；
         String  sendtime=new String();
         sendtime=formatter.format(messages[i].getSentDate());
         out.println(sendtime);
         int size=messages[i].getSize();  
         
         //执行数据库插入操作
         String ConnInsert =new String();
         ConnInsert = "jdbc:odbc:webmail";   //数据源
         Connection connectInsert =null;
         try {
           Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");   
         }
         catch(java.lang.ClassNotFoundException e) {
            System.err.println( e.getMessage());
         }
   
        try {
          
          //连接数据库
          connectInsert = DriverManager.getConnection(ConnInsert,logName,passwd);   
          Statement stmtInsert = connectInsert.createStatement();
          String sqlInsert=new String();
          //sqlInsert="insert into INBOX(ID,userID,sender,subject,size)";
          //sqlInsert+=" values('"+InboxID+"','"+userID+"','"+sender+"','"+subject+"','"+size+"')";  
          
          sqlInsert="insert into INBOX(ID,userID,sender,subject,sendtime,content,size)";
          sqlInsert+=" values('"+InboxID+"','"+userID+"','"+sender+"','"+subject+"','"+sendtime+"','"+contents+"','"+size+"')";  
          stmtInsert.executeUpdate(sqlInsert);
          
        } 
        catch(SQLException ex) { 
          System.err.println(ex.getMessage());
        }  
       
       
          /******************  判断是否附件   ************************/
        
       if(messages[i].isMimeType("multipart/*"))   //附件
       {
          FetchProfile fp=new FetchProfile(); 
          fp.add(FetchProfile.Item.ENVELOPE); 
          fp.add(FetchProfile.Item.FLAGS); 
          fp.add("X-Mailer"); 
          folder.fetch(messages,fp); 
   
          Object content=messages[i].getContent();
          Multipart multipart = (Multipart)content;
          for (int c=0, n=multipart.getCount(); c<n; c++) 
          {
                    
             Part part = multipart.getBodyPart(c); 
             
             
             
             //String msg=getStr(part.getContent());
             /***StringBuffer buf=new StringBuffer(msg.length()+6); 
                   char ch=' '; 
                   for(int u=0;u<msg.length();u++)
                   {  
                       ch=msg.charAt(u); 
                       if(ch=='\n')buf.append(""); 
                       else buf.append(ch); 
                   } 
             String mm = buf.toString();   ********/
            // out.println(new String(mm.getBytes("iso-8859-1"),"gb2312")); 
             
                         
             String disposition = null;            
             disposition = part.getDisposition();
             if ( disposition != null &&(disposition.equals(Part.ATTACHMENT) || disposition.equals(Part.INLINE)))
             {
               //String fileName=getStr(part.getFileName());  //转换成中文GB2313
               String fileName=null,AttachName =new String();
               fileName=part.getFileName();
               AttachName =fileName;             //附件文件名
               InputStream inputstream=part.getInputStream();
               if(fileName==null)
               {
                 fileName=File.createTempFile("attachment",".out").getName();
               }
               
              String filePath=new String();
              filePath="c:\\MailAttachment\\"+username+"\\" ;   // 存储路径 
              fileName=filePath+fileName;
              File file=new File(fileName);
              for(int j=0;file.exists();j++)
              {
                file=new File(fileName+j);
              }
              FileOutputStream fileoutputstream =new FileOutputStream(file);
              BufferedOutputStream bufferedoutputstream =new BufferedOutputStream(fileoutputstream);
              BufferedInputStream bufferedinputstream =new BufferedInputStream(inputstream);
          
              int m;
              while ((m=bufferedinputstream.read())!=-1)
                bufferedoutputstream.write(m);
              
              
              //save the filename
              String SqlUpdate=new String();
              SqlUpdate="UPDATE INBOX SET AttachmentName='"+AttachName+"',AttachmentPath='"+filePath+"' ";
              SqlUpdate+="WHERE ID='"+InboxID+"'";   //InboxID
              executeUpdateSql(SqlUpdate);
                         
              bufferedoutputstream.flush();
              bufferedoutputstream.close();
              bufferedinputstream.close();
            }
           }
          
       
       
       
       
       
          //out.println("Attachment2");
       } 
        
      
                                   
        connectInsert.close();     
      }  //FOR 循环结束

调用String的某些方法时候和长度有问题。

我认为可能出现问题的地方:
sender=senderAddr.substring(start+1, end);  

或者是数组越界了。