无法用Java写入文件

Question

I have been attempting to create a class that will go through a file and create a HashMap based on the values it finds and that can also write a HashMap to the same file with changed values incorporated with new and already existing ones. The reading of the file into a HashMap is working, however, when I attempt to write said HashMap back to the file with different values and keys, the file does not change what so ever. Just for clarification, I am on a UNIX-Style system: Ubuntu 14.10

public class FConfig {
  public FConfig( String pathToFile ) throws IOException {
    config = new File( pathToFile );
    if( !config.exists() ) {
      config.createNewFile();
    }
  }
  public FConfig( File file ) throws IOException {
    if( !file.isFile() ) {
      throw new IllegalArgumentException();
    }
    config = new File( file.getAbsolutePath() );
    if( !config.exists() ) {
      config.createNewFile();
    }
  }
  private final File config;
  private BufferedReader fileIn;
  private BufferedWriter fileOut;

  public HashMap<String, String> loadAllProperties() throws IOException {
    fileIn = new BufferedReader( new FileReader( config ) );
    config.setReadable( true );
    HashMap<String, String> props = new HashMap<>();
    String line;
    while( ( line = fileIn.readLine() ) != null ) {
      if( line.contains( "=" ) ) {
        props.put( line.split( "=" )[ 0 ], line.split( "=" )[ 1 ] );
      }
    }
    return props;
  }
  public void writeAllProperties( HashMap<String, String> newProps ) throws IOException {
    fileOut = new BufferedWriter( new FileWriter( config ) );
    HashMap<String, String> props = loadAllProperties();
    props.putAll( newProps );
    config.delete();
    config.createNewFile();
    config.setWritable( true );
    System.out.println( config.canWrite() );
    for( Entry<String, String> entry : props.entrySet() ) {
      System.out.println( entry.getKey() + "=" + entry.getValue() );
      fileOut.write( String.format( "%1$s=%2$s", entry.getKey(), entry.getValue() ) );
    }
    fileOut.close();
  }
}

and I am calling the method

FConfig c = new FConfig( new File( System.getProperty( "user.home" ), "fConfig.cfg" ).getAbsolutePath() );

HashMap<String, String> props = new HashMap<>();
props.put( "a", "value0" );
props.put( "c", "value1" );
props.put( "b", "value2" );
for( Entry<String, String> e : c.loadAllProperties().entrySet() ) {
  System.out.println( e.getKey() + ":" + e.getValue() );
}
try {
  c.writeAllProperties( props );
} catch( Exception e ) {
  e.printStackTrace();
}

Using GEdit I can tell that the file is being modified, but nothing actually changes in the file, I have ensured that the file is writable and readable. I am truly confused as to why this is happening as not even an exception is thrown.

Answer 1

Change the order of your commands. Create the FileWriter on your file after you create it.

public void writeAllProperties( HashMap<String, String> newProps ) throws IOException {
    // fileOut = new BufferedWriter( new FileWriter( config ) );
    HashMap<String, String> props = loadAllProperties();
    props.putAll( newProps );
    config.delete();
    config.createNewFile();
    config.setWritable( true );
    // You just created a new file.
    fileOut = new BufferedWriter( new FileWriter( config ) );

Also, if you're using Java 7+ I suggest you take advantage of the try-with-resources Statement to close() (and if you aren't, then you should call close() in a finally block)

public void writeAllProperties(HashMap<String, String> newProps)
        throws IOException {
    // fileOut = new BufferedWriter(new FileWriter(config));
    HashMap<String, String> props = loadAllProperties();
    props.putAll(newProps);
    config.delete();
    config.createNewFile();
    config.setWritable(true);
    try (BufferedWriter fileOut = new BufferedWriter(new FileWriter(config))) {
        System.out.println(config.canWrite());
        for (Entry<String, String> entry : props.entrySet()) {
            System.out.println(entry.getKey() + "=" + entry.getValue());
            fileOut.write(String.format("%1$s=%2$s", entry.getKey(),
                    entry.getValue()));
        }
    }
}

Finally , your FileWriter(File) constructor is guaranteed to create a new file (since you aren't passing in append). As such, you should really be using something like

public void writeAllProperties(HashMap<String, String> newProps)
        throws IOException {
    // fileOut = new BufferedWriter(new FileWriter(config));
    HashMap<String, String> props = loadAllProperties();
    props.putAll(newProps);
    if (!config.canWrite()) { // <-- to check if it is writable
        return;
    }
    try (BufferedWriter fileOut = new BufferedWriter(new FileWriter(config))) {
        System.out.println(config.canWrite());
        for (Entry<String, String> entry : props.entrySet()) {
            System.out.println(entry.getKey() + "=" + entry.getValue());
            fileOut.write(String.format("%1$s=%2$s", entry.getKey(),
                    entry.getValue()));
        }
    }
}