文件追加模式

淩亂°似流年 2023-02-10 05:22 15阅读 0赞

今天踩了一个坑，在分批次写入文件时，损坏了文件，后来经过排查发现，需要使用追加模式来写文件，否则每次都是从头开始写。这个就是FileInputStream的构造函数里面的一个参数决定的。

/**
         * 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);

通过append参数的描述就可以看出，这个就是决定是否是追加模式

调用时可以这样调用.

FileOutputStream outputStream  =new FileOutputStream(new File(filePath), true);