FileObject streams

Written on June 12, 2009 by Allan Lykke Christensen

As I’m still learning the NetBeans platform I was getting concerned about closing and opening streams when creating new FileObjects. I therefore posted a question on StackOverflow hoping that some NetBeans Guru would see. After posting I dug into the NetBeans API and source code and discovered how it all works. Here is the except from my self-answered question on StackOverflow:

Q: When creating modules on the NetBeans platform, the FileObject object represents a file in the virtual file system of the IDE. Creating new FileObjects is simple, but does NetBeans completely control the reference to the actual File, or should I close FileObject myself? My code is like this:

FileObject appRoot = FileUtil.getConfigRoot().getFileObject("myapp");
 
try {
    FileObject fo = servers.createData(filename);
    fo.setAttribute("name", "a name");
    fo.setAttribute("desc", "a description");
} catch (IOException ex) {
   throws new FileCreationException("Could not create file " + filename, ex);            
}

With the above code, am I leaving open some references to the actual file or should I obtains the OutputStream of the FileObject and close it manually?

Thanks.

Self-answer: After digging around in the NetBeans API and source code I believe I’ve found the answer to my own question.

Attributes as set above are stored in a special attributes file. Each folder in the virtual file system has a hidden attributes file (.nbattrs) which contains the attributes stored for each FileObject, e.g.

<!DOCTYPE attributes PUBLIC "-//NetBeans//DTD DefaultAttributes 1.0//EN"     
                            "http://www.netbeans.org/dtds/attributes-1_0.dtd">
<attributes version="1.0">
    <fileobject name="dk-i2m-netbeans-smtpdummyservice-mailserver-1244831819713">
        <attr name="name" stringvalue="My test"/>
        <attr name="desc" intvalue="Server for testing outgoing e-mails"/>
    </fileobject>
</attributes>

This file is completely controlled by NetBeans and no opening or closing of input/output streams are necessary.

If however, you want to add content to the FileObject and not mere attributes, you will have to do it the normal Java-way of using the InputStream and OutputStream of the FileObject (both have a getter and setter) and remember to close the streams accordingly. e.g.

FileObject appRoot = FileUtil.getConfigRoot().getFileObject("myapp");
 
try {
    FileObject fo = servers.createData(filename);
    fo.setAttribute("name", "a name");
    fo.setAttribute("desc", "a description");
 
    // Lock the FileObject before writing
    FileLock lock;
    try {
        lock = fo.lock();
    } catch (FileAlreadyLockedException ex) {
        Exceptions.printStackTrace(ex);
        return;
    }
 
    try {
        OutputStream out = fo.getOutputStream(lock);
        try {
            // Write into the output stream
        } finally {
            // Remember to close the stream
            out.close();
        }
    } finally {
        lock.releaseLock();
    }
} catch (IOException ex) {
    throws new FileCreationException("Could not create file " + filename, ex);            
}

Posted in Java