Thursday, 29 December 2011

Adding a directory to java.library.path

In addition to what I said before, there is actually a cool way to add a directory to java.library.path. If you launch your application via a script you can execute a commandline Java tool to output the current library path. For example, this simple Java program adds "/usr/local/lib/" to that path and prints it without a trailing CR to the console:

public class LibPath
    public static void main( String[] args )

To use it just compile it, and then invoke it in the script:

LIBPATH=`java LibPath`:/usr/local/lib
java -Djava.library.path=$LIBPATH ....

And as if by magic the java library path acquires a new directory before your prorgam is run.

Wednesday, 28 December 2011

Posting multipart form data

For testing I needed to simulate a web-browser doing a file-upload. I tried to Google this but I couldn't find a suitable answer that worked. So I rolled my own. This might save other people some trouble too. First comes the MIMEMultipart object, which stores the body of a multipart post:


public class MIMEMultipart 
    StringBuilder text;
    static String CRLF = "\r\n";
    String boundary;
    public MIMEMultipart()
        text = new StringBuilder();
        boundary = Long.toHexString(
    public String getContent()
        return text.toString();
    public String getBoundary()
        return boundary;
    public int getLength()
        return text.length();
    public void putStandardParam( String name, 
        String value, String encoding )
        StringBuilder sb = new StringBuilder();
        sb.append("--" + boundary).append(CRLF);
        sb.append("Content-Disposition: form-data; "
        sb.append("Content-Type: text/plain; charset=" 
            + encoding );
        text.append( sb.toString() );
    public void putBinaryFileParam( String name, 
        String fileName, String mimeType, 
        String encoding ) throws Exception
        // compose the header
        StringBuilder sb = new StringBuilder();
        sb.append( "--"+boundary );
        sb.append( CRLF );
        sb.append("content-disposition: form-data; "
            +"name=\"" );
        sb.append( name );
        sb.append( "\";  filename=\"");
        sb.append( fileName );
        sb.append( "\"" );
        sb.append( CRLF );
        sb.append("Content-Type: "+mimeType ); 
        sb.append( CRLF );
        sb.append("Content-Transfer-Encoding: binary");
        sb.append( CRLF ); // need two of these
        sb.append( CRLF );
        text.append( sb.toString() );
        // now for the file
        File input = new File( fileName );
        FileInputStream fis = new FileInputStream(input);
        byte[] data = new byte[(int)input.length()]; data );
        text.append( new String(data,encoding) );
        text.append( CRLF );
    public void finish()
        text.append( "--" );
        text.append( boundary );
        text.append( "--" );
        text.append( CRLF );

To call it, open a standard Java URLConnection:

private static void printResponse( 
    URLConnection conn )
        InputStream is = conn.getInputStream();
        while ( is.available() != 0 )
            byte[] data = new byte[is.available()];
   data );
            System.out.println(new String(data,
    catch ( Exception e )
        e.printStackTrace( System.out );
URL url2 = new URL("http://localhost:8080/strip");
URLConnection conn = url2.openConnection();
MIMEMultipart mmp = new MIMEMultipart();
mmp.putStandardParam( Params.FORMAT,Formats.STIL,
    "UTF-8" );
mmp.putStandardParam( Params.STYLE,"TEI/drama",
    "UTF-8" );
mmp.putBinaryFileParam( Params.RECIPE,"recipe.xml",
    "application/xml","UTF-8" );
mmp.putBinaryFileParam( Params.XML,
    "application/xml","UTF-8" );
conn.setRequestProperty("Accept-Charset", "UTF-8");
    "multipart/form-data, boundary="
OutputStream output = conn.getOutputStream();
output.write( mmp.getContent().getBytes() );
// get response and print it
printResponse( conn );

Extend MIMEMultipart if you like by adding a method for plain text files and other types of part.

Sunday, 25 December 2011

Loading native libraries in Java

This is an old problem, so I thought I'd write down my current experiences to save others, and myself, pain in future.

You write a native library or foo.dll or libFoo.dylib etc. for Java. And you store it in a convenient location, not a system location, because your software shouldn't meddle with that. To use it you need to call System.loadLibrary("foo");. This will probably give you: "Exception in thread "main" java.lang.UnsatisfiedLinkError: no foo in java.library.path". Where did I go wrong?

System.loadLibrary looks in the Java library path, "java.library.path". Cool, let's set that in the program, just before we call loadLibrary. We can get some platform-independence by passing in the library path on the commandline:

String old = System.getProperty("java.library.path");

It doesn't find the library because you can't change "java.library.path" after starting the JVM. It just ignores your additional directory.

Everyone says set the environment variable LD_LIBRARY_PATH to (in my case) /usr/local/lib. This doesn't work either. On Linux and OSX at least Java ignores that variable when setting up java.library.path. In any case setting LD_LIBRARY_PATH globally for your application will screw up something else on your system. Not cool.

Third attempt. Set java.library.path on the java commandline:


Now you've changed the JVM so things could go wrong. Instead of having the system default library path where everything is, you've redefined it to a custom location. Unfortunately there's no universal way to ADD /usr/local/lib to java.library.path. So the best you can do is find the java library path on your system (by writing a Java program that outputs System.getProperty("java.library.path")) and then add /usr/local/lib to that value and finally specify the entire string to java:


This is what I have to do on Mac OSX. Of course it's entirely platform-specific, which is stupid for a programming language that is supposed to be platform-independent. On the other hand this yucky solution is the best one on offer. Since when you've finished developing you'll be running it time and time again on the same platform it probably doesn't matter much.

Alternatively, you could just put your library in the current directory, which will work on Windows (reportedly) and Mac OSX but not Linux.

Saturday, 24 December 2011

Installing couchdb on Mac OSX

Installing couchdb on Linux is a breeze. At least with the Debian package manager. But on OSX, where I was stuck over the Christmas break, installation is a pain. Of course if you believe the hype homebrew will save us. All you have to do is install it and type: brew install couchdb. Except that, it doesn't work. Packages have to be maintained, and unless the homebrew authors do all that work, their packeges will soon break. So I had to do it myself. This is the formula on 64 bit systems:

  1. Download the latest Erlang source. Configure with --enable-darwin-64bit . Otherwise it compiles in 32 bit and it won't work with the other components, especially icu. Then make, make install as usual.
  2. Download and install ICU (configure, make, make install)
  3. Download and install couchdb. Configure, make, make install. And it all should work.

Now that Apple's great leader has passed on maybe someone in charge will see that a proper package manager would be a good idea for OSX.