A servlet to display the (public) files in your web root.

DirectoryServlet.java

package com.service.file;

import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Collection;
import java.util.logging.Level;
import java.util.logging.Logger;

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

/**
 * Displays the files in your web root. Includes flags to hide internal files
 * (INF folders, JSP pages, etc). This is a less-secure alternative for file
 * downloads. Requires SDK 6 and Java EE 6. If your using a previous version,
 * revert back to using web.xml for your mappings.
 * 
 * @author Ryan Beckett
 */
@WebServlet("/DirectoryServlet")
public final class DirectoryServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;
    private PrintWriter out;
    private final Logger console = Logger.getLogger("DirectorySerlvet");
    private static final boolean hideInternal = true;
    private static final String[] internalFileExtensions = { "html", "xhtml",
            "jsp", "inf" };

    public DirectoryServlet() {
        super();
    }

    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        setHtmlOutputStream(response);
        File dir = parseDirectory(request);
        File[] files = listFiles(dir);
        Collection<String> anchors = createFileAnchors(dir, files);
        String dirPath = getPathRelativeToParent(getWebRootAsFile(),
                dir);
        renderPage(dirPath, anchors);
    }

    private File parseDirectory(HttpServletRequest request) {
        String dir = request.getParameter("dir");
        if (dir == null)
            return new File(getRealPathOfWebRoot());
        else
            return new File(getRealPathOfWebRoot() + dir);
    }

    private String getRealPathOfWebRoot() {
        return this.getServletContext().getRealPath("");
    }

    private File[] listFiles(File dir) {
        return dir.listFiles();
    }

    private Collection<String> createFileAnchors(File parent, File[] files) {
        Collection<String> anchors = new ArrayList<String>();
        if (files != null) {
            for (File file : files) {
                if (canShowFile(file)) {
                    String anchorTag = createAnchorTag(file);
                    if (anchorTag != null)
                        anchors.add(anchorTag);
                }
            }
        }
        return anchors;
    }

    private boolean canShowFile(File file) {
        if (hideInternal) {
            if (isInternal(file))
                return false;
        }
        return true;
    }

    private boolean isInternal(File file) {
        String fileName = file.getName();
        for (String ext : internalFileExtensions)
            if (fileName.toLowerCase().endsWith(ext))
                return true;
        return false;
    }

    private String createAnchorTag(File file) {
        if (file.isDirectory())
            return createDirectoryAnchorTag(file);
        else
            return createFileAnchorTag(file);
    }

    private String createDirectoryAnchorTag(File file) {
        return "<a href=\"" + getWebRootName() + "/DirectoryServlet?dir="
                + getPathRelativeToParent(getWebRootAsFile(), file) + "\">"
                + file.getName() + "</a>";
    }

    private String createFileAnchorTag(File file) {
        return "<a href=\""
                + getPathRelativeToParent(getWebRootAsFile().getParentFile(),
                        file) + "\">" + file.getName() + "</a>";
    }

    private void renderPage(String dir, Collection<String> anchors) {
        printOpeningHtmlTags();
        if (dir.equals(""))
            dir = getWebRootName();
        printHtml("<h1>Index of " + dir + "</h1><br/>");
        for (String link : anchors)
            printHtml(link + "<br/>");
        printClosingHtmlTags();
    }

    private String getPathRelativeToParent(File parent, File file) {
        String[] tokens = file.getAbsolutePath()
                .split(parent.getAbsolutePath());
        if (tokens.length < 2)
            return "/";
        else
            return tokens[1];
    }

    private String getWebRootName() {
        return this.getServletContext().getContextPath();
    }

    private File getWebRootAsFile() {
        return new File(getRealPathOfWebRoot());
    }

    private void setHtmlOutputStream(HttpServletResponse response) {
        try {
            out = response.getWriter();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private void printHtml(String html) {
        out.print(html);
    }

    private void printErrorHtml() {
        printHtml("There was an error.<br/>");
    }

    private void printOpeningHtmlTags() {
        out.print("<html><head><title>Directory</title></head><body><div>");
    }

    private void printClosingHtmlTags() {
        out.print("</div></body></html>");
    }

    private void logToConsole(String message) {
        console.log(Level.INFO, message);
    }

}