How to download a file via a button click i GWT?

Question

I hava a servleta that serves files?

I\'m building a page with a \"Download\" button usung a GWT.

How to make a GWT client download a file in an onClick even

Answer 1

COMPLETE EXAMPLE TO DOWNLOAD a .xls FILE USIGN GWT,apache-poi

    Environment : GWT SDK 2.4
    Spring 3.0.2M
    JAVA : 1.7

Needed Jar file to create .xls file :: poi-3.0.1-FINAL.jar

exportButton.addClickHandler(new ClickHandler() {

@Override
public void onClick(ClickEvent event) {
     String link = GWT.getModuleBaseURL() + "myfiledownload";
     Window.open(link , "", "");
    }//onClick
});//addClickHandler

Now at the browser when the user hits button exportButton then the control navigates to web.xml and searches for url-pattern that ends with /myfiledownload

web.xml

    
        fileDownload
        com.sbabamca.server.FileDownloadServlet
    
    
        fileDownload
        /app/myfiledownload
    

After execuiting the code in web.xml the controls tries to execute the servlet with name FileDownloadServlet

SERVER SIDE

    FileDownloadServlet.java
    ------------------------    

    package com.sbabamca.server;

    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.ServletException;
    import org.apache.poi.hssf.usermodel.HSSFRow;
    import org.apache.poi.hssf.usermodel.HSSFSheet;
    import org.apache.poi.hssf.usermodel.HSSFWorkbook;
    import org.hibernate.Query;
    import org.hibernate.Session;
    import org.hibernate.SessionFactory;
    import org.hibernate.Transaction;
    import org.hibernate.metadata.ClassMetadata;
    import com.fpix.hibernate.util.HibernateUtil;
    import com.fpix.util.date.MyDate;
    import java.io.IOException;
    import java.util.ArrayList;

    public class MyFileServlet extends HttpServlet {
    SessionFactory sessionFactory;
    Session session;
    Transaction tx = null;


        @SuppressWarnings({ "unchecked", "deprecation" })
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

                resp.setContentType("application/vnd.ms-excel");
                resp.setHeader("Content-Disposition", "attachment; filename=users.xls");
                try {

                    sessionFactory = HibernateUtil.getSessionFactory();
                    if(!sessionFactory.getCurrentSession().isOpen())
                    {
                        session = sessionFactory.openSession();
                    }
                    else
                    {
                    session = sessionFactory.getCurrentSession();
                    }
                    tx = session.beginTransaction();
                    tx.begin();

                    Query qry = session.createQuery("from com.fpix.dto.User u ");
                    ArrayList u = (ArrayList)qry.list();

                    Query qry1 = session.createQuery("from com.fpix.dto.Profile p ");
                    ArrayList p = (ArrayList)qry1.list();

                    /*
                     * code to get the column name of User and Profile Entity
                     */
                    ClassMetadata cm = sessionFactory.getClassMetadata(com.fpix.dto.User.class);
                    String userAttributes[] = cm.getPropertyNames();

                    ClassMetadata cm1 = sessionFactory.getClassMetadata(com.fpix.dto.Profile.class);
                    String profileAttributes[] = cm1.getPropertyNames();

                     HSSFWorkbook wb = new HSSFWorkbook();
                     HSSFSheet sheet = wb.createSheet("Excel Sheet");
                     HSSFRow rowhead = sheet.createRow((short) 0);

                     rowhead.createCell((short) 0).setCellValue("id");
                     /*
                      * code to create the columns names in .xls file
                      */
                     int j = 0;
                     for(int i=0;i