Java FileWriter覆盖

Question

我有一段代码，只要有新数据可以作为InputStream使用，它就会生成新数据。每次都会覆盖相同的文件。有时，文件在写入之前就会变成0kb。webservice服务定期读取这些文件。我需要避免当文件是0字节时的情况。

它是如何做到这一点的？锁在这种情况下会有帮助吗？如果浏览器读取锁定的文件，浏览器是否会继续显示缓存中的旧数据，直到锁定解除，文件可供再次读取。

try{
String outputFile = "output.html";     
FileWriter fWriter = new FileWriter(outputFile);
//write the data ...

fWriter .flush();


outputFile = "anotheroutput.html";     
fWriter = new FileWriter(outputFile);
//write the data ...

fWriter .flush();
fWriter.close();
}
catch(Exception e)
{
 e.prinStackTrace();
}

Answer 1

尝试写入一个临时文件(在同一文件系统中)，完成文件写入后，使用File.renameTo()将其移动到适当的位置。如果您的底层文件系统支持原子移动操作(大多数支持)，那么您应该获得所需的行为。如果你在windows上运行，你必须确保在读取后关闭文件，否则文件移动将失败。

public class Data
{
    private final File file;
    protected  Data(String fileName) {
        this.file = new File(filename);
    }

   /* above is in some class somehwere 
    *  then your code brings new info to the file
    */

   // 
   public synchronized accessFile(String data) {
       try {
           // Create temporary file
           String tempFilename = UUID.randomUUID().toString() + ".tmp";
           File tempFile = new File(tempFilename);

           //write the data ...
           FileWriter fWriter = new FileWriter(tempFile);
           fWriter.write(data);
           fWriter.flush();
           fWriter.close();

           // Move the new file in place
           if (!tempFile.renameTo(file)) {
               // You may want to retry if move fails?
               throw new IOException("Move Failed");
           }
       } catch(Exception e) {
           // Do something sensible with the exception.
           e.prinStackTrace();
       }
   }
}

Answer 2

FileWriter fWriter = new FileWriter(fileName,true);

尝试使用上面的:-)

Answer 3

public class Data
{
  String fileName;
  protected  Data(String fileName)
  {
     this.fileName= fileName;
     return; // return from constructor often not needed.
  }

   /* above is in some class somehwere 
    *  then your code brings new info to the file
    */

  // 
  public synchronized accessFile(String data)
  {
    try
    {
       // File name to be class member.
       FileWriter fWriter = new FileWriter(fileName);
       //write the data ...
       fWriter.write(data);
       fWriter .flush();
       fWriter .close();
       return;
    }
    catch(Exception e)
    {
       e.prinStackTrace();
    }

这不是必需的：

 outputFile = "anotheroutput.html";     
 fWriter = new FileWriter(outputFile);
 //write the data ...

fWriter .flush();
fWriter.close();

这是因为处理文件是类数据的一种方法