FileNotFoundException：FileOutputStream

源码：

/**
     * Creates a file output stream to write to the file with the
     * specified name. 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 <code>name</code> 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      name   the system-dependent filename
     * @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.lang.SecurityManager#checkWrite(java.lang.String)
     */
    public FileOutputStream(String name) throws FileNotFoundException {
        this(name != null ? new File(name) : null, false);
    }

  /**
     * Opens a file, with the specified name, for overwriting or appending.
     * @param name name of file to be opened
     * @param append whether the file is to be opened in append mode
     */
    private native void open0(String name, boolean append)
        throws FileNotFoundException;

注释说的很清楚，1.如果是个目录而不是具体文件；2.文件不存在但是不能被创建；3.因为其他原因不能被创建

解决方法：

1. 打开文件输出流之前先判断文件夹是否存在, 比如/www/data/test.json 是需要打开的文件，先判断/www/data/目录是否存在，如果目录不存在，创建目录。

2.文件夹创建之后，然后判断文件是否存在，不存在则创建空文件

File folder = new File(OUT_RESULT);
            if(!folder.exists()){  //打开文件输出流之前先判断文件夹是否存在
                boolean created = folder.mkdirs();
                if(!created){
                    //如果目录创建失败
                    logger.warn("File output folder created failure:" + OUT_RESULT);
                    throw new FileNotFoundException(OUT_RESULT);
                }
                File file = new File(outPath);
                if(!file.exists()){
                    file.createNewFile();
                }
            }

最后再打开文件流

new FileOutputStream(outPath)