Appending to a File in Java ME ( J2ME )

Yesterday I was asked how to append to a file in Java ME. I have never done this before, so I could not give an answer. After some research we found a working solution. This article will go through the different ways to solve it.

I first looked into the JSR-75 documentation, but I did not find any solution there. When searching the Internet, the first solution I found was this:

public void appendToFile() {
try {
 FileConnection fileConnection = (FileConnection) Connector.open(
         "file:///c:/other/textfile.txt;append=true",
         Connector.WRITE);
 OutputStream outputStream = fileConnection.openOutputStream();
 PrintStream printStream = new PrintStream(outputStream);
 printStream.println("Some text to append");
} catch (IOException e) {
 e.printStackTrace();
}
}

At first it looks promising. The Connector class specifies that you could add parameters when opening a connection. However the parameters for JSR-75 are not standardized. This solution was mentioned in the Nokia developer forums, so I guess that it works on Nokia phone. The platform that we uses did not support it. Thus this solution is not portable across different Java ME devices. I recommend that you DO NOT use a solution like this.

The next solution I found looked like this:

public void appendToFileFileSize() {

try {
   FileConnection fileConnection = (FileConnection) Connector.open(
           "file:///c:/other/textfile.txt", Connector.WRITE);
   OutputStream outputStream = fileConnection.openOutputStream();
   outputStream.flush();
   long fileSize = fileConnection.fileSize();
   String textToAppend = "Some text to append";
   outputStream.write(textToAppend.getBytes(), (int)fileSize, textToAppend.length());
} catch (IOException e) {
   e.printStackTrace();
}
}

This works but is rather clumsy and does not look clean. Note that you need to call flush() before you make a call to fileSize(), otherwise the size is not guaranteed to be correct. But wait, there is another solution.

public void appendToFileMaxLong(){
try {
 FileConnection fileConnection = (FileConnection) Connector.open(
   "file:///c:/other/textfile.txt", Connector.WRITE);
 OutputStream outputStream = fileConnection.openOutputStream(Long.MAX_VALUE);
 PrintStream printStream = new PrintStream(outputStream);
 printStream.println("Some text to append");
} catch (IOException e) {
 e.printStackTrace();
}
}

The method openOutputStream(long bytesOffset) open an OutputStream and moves the position the specified offset. When the offset is greater than the file size, the position is moved to the end of the file. This is an clean and portable solution.