JSP 读取器/写入器无法正常工作答案

【问题标题】：JSP Reader/Writer not working correctlyJSP 读取器/写入器无法正常工作
【发布时间】：2012-07-10 15:17:45
【问题描述】：

我正在尝试创建一个 JavaServer Page，它读取两个文本文件（dev.txt 和 BLTversion.txt）并让用户写入它们以更新其内容。唯一的问题是用户尝试更新 BLTversion.txt 时，它会删除文件内容......所以我认为写作部分有问题？我将继续尝试得到这个，但只是想我会发布它，以防在我弄清楚之前有人能看到我哪里出错了。这是代码：

    <%

ArrayList list = new ArrayList();
ArrayList list2 = new ArrayList();
String line1 = "";
String line2 = "";
boolean error = false;
String errorString = "";

String original = request.getParameter("original");
String code = request.getParameter("code");
String prod = request.getParameter("prod");
String versions = request.getParameter("versions");
String engineer = request.getParameter("engineer");
String assignee = request.getParameter("assignee");
line1 = prod + "," + code + "," + engineer.toUpperCase() + "," + assignee.toUpperCase() + "," + versions;
line2 = code + " " + versions + ",";

if(code.matches("(?i),* ,*")){
    errorString = errorString + "Your product code contains a space and is not valid <br />";
    error = true;
}

if(versions.matches("(?i),* ,*")){
    errorString = errorString + "Your versions contains a space and are not valid <br />";
    error = true;
}

if(engineer.equals("")){
    errorString = errorString + "Please enter an Engineer<br />";
    error = true;
}

if(assignee.equals("")){
    errorString = errorString + "Please enter an Assignee<br />";
    error = true;
}

File f = new File(Properties + seperator + "dev.txt");
File f2 = new File(Properties + seperator + "BLTversion.txt");

if (error){
    out.println(errorString);
}
else{
   try{       
       FileInputStream fstream = new FileInputStream(f);

       DataInputStream in = new DataInputStream(fstream);
       BufferedReader br = new BufferedReader(new InputStreamReader(in));
       String strLine;

       while ((strLine = br.readLine()) != null)   {
           String[] langs = strLine.split(",");

           if (!langs[1].equals(original)){
               list.add(strLine);
           }
       }
       br.close();

   }
   catch (Exception e){//Catch exception if any
       System.err.println("Error: " + e.getMessage());
   }
   if (error){
     out.println(errorString);
   }
   else{
       list.add(line1);
       Collections.sort(list);
       try{
           Writer update = new BufferedWriter(new FileWriter(f));
           for (int i = 0; i < list.size(); i++) {
               if (i == (list.size() - 1)){
                   update.write((String) list.get(i));
               }
               else{
                   update.write((String) list.get(i) + newLineChar);
               }
           } 
           update.close();
       }
       catch (Exception e){//Catch exception if any
           System.err.println("Error: " + e.getMessage());
           out.println("Your Product was not correctly processed, Please try again");
       }
   }

   try{
       FileInputStream fstream2 = new FileInputStream(f2);

       DataInputStream in2 = new DataInputStream(fstream2);
       BufferedReader br2 = new BufferedReader(new InputStreamReader(in2));
       String strLine2;

       while ((strLine2 = br2.readLine()) != null)   {
           String[] langs = strLine2.split("\\s");

           if (!langs[1].equals(original)){
               list2.add(strLine2);
           }

       }
       br2.close();

   }
   catch (Exception e){//Catch exception if any
       System.err.println("Error: " + e.getMessage());
   }
   if (error){
       out.println(errorString);
   }
   else{
       list2.add(line2);
       Collections.sort(list2);

       try{
           Writer update2 = new BufferedWriter(new FileWriter(f2));

           for (int i = 0; i < list.size(); i++) {
               if (i == (list2.size() - 1)){
                   update2.write((String) list2.get(i));
               }
               else{
                   update2.write((String) list2.get(i) + newLineChar);
               }  
           } 

           update2.close();
       }
       catch (Exception e){//Catch exception if any
           System.err.println("Error: " + e.getMessage());
           out.println("Your Product was not correctly processed, Please try again");
       }
   }
}    
  %>

【问题讨论】：

1) 在 JSP 中包含 java 代码并不是最佳实践。 2）有什么问题？你有什么错误吗？
@thinksteep 问题在于，它没有写入 BLTversion.txt 文件（参见第一个 try 语句之前的文件 f2）来更新它，它只是删除其所有内容并将其保留为空文本文件。没有错误，因为没有任何语法错误，只是假设它写入 BLTversion.txt 文件的部分的逻辑有问题。
请注意，写入文件系统会使您的 Web 应用程序供应商依赖，因为您超出了 servlet API 保证的工作范围，

标签： java jsp bufferedreader bufferedwriter

【解决方案1】：

使用

new FileWriter( fileName, append );

其中 append 应为 true 以保留现有文件内容并附加新内容。

参考：

【讨论】：