ContentServlet.java

import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Locale;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.google.inject.Inject;
import com.google.inject.name.Named;

public abstract class ContentServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;
    
    private ThreadLocal<SimpleDateFormat> format = new ThreadLocal<SimpleDateFormat>() {
        protected SimpleDateFormat initialValue() {
            return new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss zzz", Locale.ENGLISH);
        }
    };

    private String content;
    
    @Inject
    @Named("developmentMode")
    private boolean developmentMode;
    
    private final Date modifiedSince = Calendar.getInstance().getTime();
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException,
            IOException {
        
        resp.setContentType(getContentType());
        String modifiedHeader = req.getHeader("If-Modified-Since");
        Date mod = null;
        
        if (modifiedHeader != null) {
            try {
                mod = format.get().parse(modifiedHeader);
            } catch (Exception e) {
                // Just ignore
            }
        }
        
        if (mod != null && modifiedSince.before(mod)) {
            resp.sendError(HttpServletResponse.SC_NOT_MODIFIED);
        } else {
            resp.getWriter().print(content);
        }
    }
    
    protected abstract String getContentType();

    public boolean isDevelopmentMode() {
        return developmentMode;
    }

    public void setContent(String content) {
        this.content = content;
    }
}

CssMinifierServlet.java

import java.io.InputStreamReader;
import java.io.StringWriter;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.List;

import net.contextfw.web.application.DocumentProcessor;
import net.contextfw.web.application.WebApplicationException;

import org.dom4j.Document;
import org.dom4j.Element;

import com.google.inject.Inject;
import com.google.inject.Singleton;
import com.google.inject.name.Named;
import com.yahoo.platform.yui.compressor.CssCompressor;

@Singleton
public class CssMinifierServlet extends ContentServlet implements DocumentProcessor {

    private static final long serialVersionUID = 1L;

    @Inject
    @Named("host")
    private String host;
    
    @Inject
    @Named("started")
    private String started;

    @Override
    public void process(Document document) {
        
        if (isDevelopmentMode()) return;
        
        List<Element> links = document.selectNodes("//html/head/link");
        
        StringBuilder sb = new StringBuilder();
        for (Element script : links) {
            String src = script.attributeValue("href");
            if (src.startsWith("{$contextPath}")) {
                src = src.replace("{$contextPath}", "");
                URL url;
                try {
                    url = new URL(host + src);
                    sb.append(compress(url)).append("\n");
                } catch (MalformedURLException e) {
                    e.printStackTrace();
                }
            }
        }
        setContent(sb.toString());
        
        links.get(0).addAttribute("href", "{$contextPath}/minified-"+started+".css");
        
        for (int i = 1; i < links.size(); i++) {
            links.get(i).detach();
        }
    }
    
    private String compress(URL url) {
        try {
            CssCompressor compressor = new CssCompressor(new InputStreamReader(url.openStream()));
            StringWriter writer = new StringWriter();
            compressor.compress(writer, 0);
            return writer.toString();
        } catch (Exception e) {
            throw new WebApplicationException(url.toString(), e);
        }
    }

    @Override
    protected String getContentType() {
        return "text/css";
    }
}

JsMinifierServlet.java

import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.List;

import net.contextfw.web.application.DocumentProcessor;
import net.contextfw.web.application.WebApplicationException;

import org.apache.commons.io.IOUtils;
import org.dom4j.Document;
import org.dom4j.Element;

import com.google.inject.Inject;
import com.google.inject.Singleton;
import com.google.inject.name.Named;
import com.google.javascript.jscomp.Compiler;
import com.google.javascript.jscomp.CompilerOptions;
import com.google.javascript.jscomp.JSSourceFile;

@Singleton
public class JsMinifierServlet extends ContentServlet implements DocumentProcessor {

    private static final long serialVersionUID = 1L;
    
    @Inject
    @Named("host")
    private String host;
    
    @Inject
    @Named("started")
    private String started;
    
    @Override
    public void process(Document document) {
        
        if (isDevelopmentMode()) return;
        
        List<Element> scripts = document.selectNodes("//html/head/script[@src]");
        
        StringBuilder sb = new StringBuilder();
        for (Element script : scripts) {
            String src = script.attributeValue("src");
            if (src.startsWith("{$contextPath}")) {
                src = src.replace("{$contextPath}", "");
                URL url;
                try {
                    url = new URL(host + src);
                    if (src.contains("jquery")) {
                        sb.append(IOUtils.toString(url.openStream())).append("\n");
                    } else {
                        sb.append(compress(url)).append("\n");
                    }
                } catch (MalformedURLException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        
        scripts.get(0).addAttribute("src", "{$contextPath}/minified-"+started+".js");
        
        for (int i = 1; i < scripts.size(); i++) {
            scripts.get(i).detach();
        }
        
        setContent(sb.toString());
    }
    
    private String compress(URL url) {
        try {
            CompilerOptions options = new CompilerOptions();
            Compiler compiler = new Compiler();
            JSSourceFile source = JSSourceFile.fromInputStream(url.getFile(), url.openStream());
            compiler.compile(new JSSourceFile[] {}, new JSSourceFile[] {source} , options);
            return compiler.toSource();
        } catch (Exception e) {
            throw new WebApplicationException(url.toString(), e);
        }
    }

    @Override
    protected String getContentType() {
        return "application/javascript";
    }
}