FileOutputStream 删除文件的内容[重复]答案

【问题标题】：FileOutputStream Deletes Contents of File [duplicate]FileOutputStream 删除文件的内容[重复]
【发布时间】：2016-10-09 19:30:01
【问题描述】：

您好，我正在尝试使用 FileOutputStream 通过网络发送数据。每当使用链接的文件创建 FileOutputStream 时，它都会删除找到的所有数据，就好像它正在用新文件替换旧文件一样。

有人可以帮忙吗？这是代码。

File videoFile = new File (Current_video_file);

log.info(videoFile.toString());

InputStream is = null; 
OutputStream outS = null;

try{
    is = socket.getInputStream();
} catch (IOException e){
    e.printStackTrace();
}

try{
    outS = new FileOutputStream(videoFile);
} catch (IOException e){
    e.printStackTrace();
}

byte [] videoLength = new byte [16*1024];

log.info("About to send");
int count; 
while((count = is.read(videoLength)) > 0){
    log.info("Sending Message");
    outS.write(videoLength, 0, count);
}

log.info("Data Sent");

outS.close();
is.close();

【问题讨论】：

提示：你可以自助；例如，开始阅读您打算使用的库类/方法的 javadoc。换句话说：你做出假设这个或那个应该如何工作。事情是：现实并不关心你的假设。这并不意味着粗鲁，而是对程序员的重要教训：始终验证您的想法，其他组件的实际行为方式。尤其是当它有很好的文档时，这部分真的很容易。

标签： java sockets fileoutputstream

【解决方案1】：

JavaDoc 说明如下

/**
 * Creates a file output stream to write to the file represented by 
 * the specified <code>File</code> object. If the second argument is
 * <code>true</code>, then bytes will be written to the end of the file
 * rather than the beginning. A new <code>FileDescriptor</code> object is
 * created to represent this file connection.
 * <p>
 * First, if there is a security manager, its <code>checkWrite</code> 
 * method is called with the path represented by the <code>file</code> 
 * argument as its argument.
 * <p>
 * If the file exists but is a directory rather than a regular file, does
 * not exist but cannot be created, or cannot be opened for any other
 * reason then a <code>FileNotFoundException</code> is thrown.
 *
 * @param      file               the file to be opened for writing.
 * @param     append      if <code>true</code>, then bytes will be written
 *                   to the end of the file rather than the beginning
 * @exception  FileNotFoundException  if the file exists but is a directory
 *                   rather than a regular file, does not exist but cannot
 *                   be created, or cannot be opened for any other reason
 * @exception  SecurityException  if a security manager exists and its
 *               <code>checkWrite</code> method denies write access
 *               to the file.
 * @see        java.io.File#getPath()
 * @see        java.lang.SecurityException
 * @see        java.lang.SecurityManager#checkWrite(java.lang.String)
 * @since 1.4
 */
public FileOutputStream(File file, boolean append)

因此要使用它，您应该在 FileOutputStream 的构造函数中添加一个布尔值，True 表示追加或 False 表示覆盖

所以你的代码应该是这样的：

Boolean append = true;
outS = new FileOutputStream(videoFile, append);

【讨论】：

【解决方案2】：

FileOutputStream 的构造函数还有第二个参数可用。如果为真，它将在文件末尾附加您的数据；如果为 false，它将替换内容。默认为假。

所以您只需要更改 FileOutputStream 的声明：

outS = new FileOutputStream(videoFile, true);

【讨论】：