Compile LESS with Java

Simple Note

From official site:

For production and especially if performance is important, we recommend pre-compiling using node or one of the many third party tools.

This article describe how to compile .less file to .css file in java code on server start-up.

Pre-request

LESS Getting Started
http://ben-bai.blogspot.tw/2013/10/less-getting-started.html

Do Something on Server Startup/Shutdown
http://ben-bai.blogspot.tw/2013/10/do-something-on-server-startupshutdown.html

Result

The same as the result in previous post.

Required jars

lesscss-engine-1.3.3.jar
http://mvnrepository.com/artifact/com.asual.lesscss/lesscss-engine/1.3.3

rhino-1.7R4.jar
http://mvnrepository.com/artifact/org.mozilla/rhino/1.7R4

commons-logging-1.1.1.jar
http://mvnrepository.com/artifact/commons-logging/commons-logging/1.1.1

Code

test.less

Copied from previous post, nothing changed.

https://github.com/benbai123/JSP_Servlet_Practice/blob/master/Practice/LESS/CompileLESSWithJava/WebContent/resources/less/test.less

less_test.html

Modified from previous post, load compiled css file instead of less file and do not load less.js.

https://github.com/benbai123/JSP_Servlet_Practice/blob/master/Practice/LESS/CompileLESSWithJava/WebContent/less_test.html

TestServletContextListener.java

Implements ServletContextListener, will compile less file to css file on server start-up.

package test;

import java.io.File;
import java.io.IOException;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

import com.asual.lesscss.LessException;

import test.util.LESSUtils;

public class TestServletContextListener implements ServletContextListener {
    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        // do nothing on server shutdown
    }
    // compile less on server startup
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        try {
            String webContentPath = sce.getServletContext().getRealPath("/");
            LESSUtils.compile(new File(webContentPath + File.separator + "resources" + File.separator + "less" + File.separator + "test.less"),
                    new File(webContentPath + File.separator + "resources" + File.separator + "css" + File.separator + "test.css"));
        } catch (LessException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

LESSUtils.java

Contains utility function to compile less file, say Utils means (probably) will add more functions in future work.

package test.util;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;

import com.asual.lesscss.LessEngine;
import com.asual.lesscss.LessException;

public class LESSUtils {
    public static void compile (File lessFile, File cssFile) throws LessException, IOException {
        if (lessFile == null 
                || !lessFile.exists()) {
            // less file should exist
            throw new FileNotFoundException("LESS file not exists !");
        }
        // create less engine
        LessEngine engine = new LessEngine();
        if (!cssFile.getParentFile().exists()) {
            // create folders for css file
            boolean cssFileCreated = cssFile.getParentFile().mkdirs();
            if (!cssFileCreated) {
                throw new IOException("Folders for CSS file are not created !");
            }
        }
        // compile less file to css file
        engine.compile(lessFile, cssFile);
    }
}

web.xml

Define listener.

https://github.com/benbai123/JSP_Servlet_Practice/blob/master/Practice/LESS/CompileLESSWithJava/WebContent/WEB-INF/web.xml

References

Java Compiler for Less CSS?
http://stackoverflow.com/questions/9739724/java-compiler-for-less-css

LESS Engine
https://github.com/asual/lesscss-engine

Download

Full project at github
https://github.com/benbai123/JSP_Servlet_Practice/tree/master/Practice/LESS/CompileLESSWithJava