uploader.java

/**
 * Here an example using servlet 3.0 to upload file with file-uploader
 */
package com.silyan.simplex.view.site.content;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;

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

/**
 * Example of Servlet 3.0 used for valums-file-uploader.
 * 
 * Patch problem generated by use "multipart/form-data" request in same browsers and "application/x-www-form-urlencoded" in others.
 * By this problem, could not use @MultipartConfig features.
 * 
 * Other solution is use two servlets, one for "multipart/form-data" request and other one for "application/x-www-form-urlencoded" request, and
 * change url target in client (using javascript to detect browser).
 * 
 * @author Angel Cervera Claudio (angelcervera@silyan.com)
 *
 */
@WebServlet(name="UploadResourceServlet", urlPatterns="/upload",
        initParams={
            @WebInitParam(description="Max size in bytes", name="maxLength", value="2097152") /*2Mb = 1024×1024×2*/,
            @WebInitParam(description="Path where will be stored files", name="targetPath", value="/tmp/")
        }
)
public class UploadResourceServlet extends HttpServlet {

    /**
     * 
     */
    private static final long serialVersionUID = -4887583429734715110L;

    /**
     * limit length. 
     */
    private Long maxLength;

    /**
     * Path where will be stored files
     */
    private String targetPath;

    /* (non-Javadoc)
     * @see javax.servlet.GenericServlet#init(javax.servlet.ServletConfig)
     */
    @Override
    public void init(ServletConfig servletConfig) throws ServletException {
        super.init(servletConfig);
        maxLength = new Long( getInitParameter("maxLength") );
        targetPath = getInitParameter("targetPath");
        if(targetPath.lastIndexOf(File.separatorChar) != 0) {
            targetPath = targetPath + File.separatorChar;
        }
    }

    /* (non-Javadoc)
     * @see javax.servlet.http.HttpServlet#doPost(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
     */
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String length = request.getHeader("content-length");
        if( length == null || Long.valueOf(length) > maxLength) {
            PrintWriter pw = response.getWriter();
            pw.write("{\"error\":\"Max length (" + maxLength+ "bytes) exceed or it's null\"}");
            return;
        }

        if( isMultipartContent(request) ) {
            Part part = request.getPart("qqfile");
            String fileName = getFileNameFromPart(part);
            writeUploadedResource(fileName, part.getInputStream());
        } else {
            writeUploadedResource(request.getParameter("qqfile"), request.getInputStream());
        }
    }

    /**
     * Write in target directory.
     * 
     * @param fileName
     * @param is
     * @throws FileNotFoundException
     * @throws IOException
     */
    private void writeUploadedResource(String fileName, InputStream is) throws FileNotFoundException, IOException {
        OutputStream os = new FileOutputStream(targetPath + fileName );

    byte[] buffer = new byte[4096];
    long count = 0;
    int n = 0;
    while (-1 != (n = is.read(buffer))) {
        os.write(buffer, 0, n);
        count += n;
    }

        os.flush();
        os.close();
        is.close();
    }

    /**
     * Utility method that determines whether the request contains multipart
     * content.
     * 
     * Extract from commons-fileupload source.
     *
     * @param request The servlet request to be evaluated. Must be non-null.
     *
     * @return <code>true</code> if the request is multipart;
     *         <code>false</code> otherwise.
     */
    public static final boolean isMultipartContent( HttpServletRequest request) {
    if (!"post".equals(request.getMethod().toLowerCase())) {
        return false;
    }
    String contentType = request.getContentType();
    if (contentType == null) {
        return false;
    }
    if (contentType.toLowerCase().startsWith("multipart/")) {
        return true;
    }
    return false;
    }

    /**
     * Return filename from part.
     * 
     * @param part
     * @return
     */
    public static final String getFileNameFromPart(Part part) {
    for (String cd : part.getHeader("content-disposition").split(";")) {
        if (cd.trim().startsWith("filename")) {
            return cd.substring(cd.indexOf('=') + 1).trim().replace("\"", "");
        }
    }
    return null;

    }

}

patch: In the end of doPost method, is needed return "success", so it's necesary add tow lines:

response.setContentType("text/html");
response.getWriter().append("{success:true}");

response.getWriter().append("{success:true}"); is wrong

response.getWriter().append("{"success":true}"); is Ok