GWTでファイルをダウンロードする

GWTでファイルをダウンロードするサンプルをメモします。

画面に何かのボタンのイベントに呼び出して、ファイルをダウンロードする。

DownloadIFrame.java

package gwtsample.client;
import com.google.gwt.event.dom.client.HasLoadHandlers;
import com.google.gwt.event.dom.client.LoadEvent;
import com.google.gwt.event.dom.client.LoadHandler;
import com.google.gwt.event.shared.HandlerRegistration;
import com.google.gwt.user.client.ui.Frame;
import com.google.gwt.user.client.ui.RootPanel;
public class DownloadIFrame extends Frame implements LoadHandler, HasLoadHandlers
{
    public static final String DOWNLOAD_FRAME = "__gwt_downloadFrame";
    public DownloadIFrame(String url)
    {
        super();
        setSize("0px", "0px");
        setVisible(false);
        RootPanel rp = RootPanel.get(DOWNLOAD_FRAME);
        if (rp != null)
        {
            addLoadHandler(this);
            rp.add(this);
            setUrl(url);
        }
        else
            openURLInNewWindow(url);
    }
    native void openURLInNewWindow(String url) /*-{
        $wnd.open(url);
    }-*/;
    public HandlerRegistration addLoadHandler(LoadHandler handler)
    {
        return addHandler(handler, LoadEvent.getType());
    }
    public void onLoad(LoadEvent event)
    {}
}

ServletUtils.java

package gwtsample.server;
import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ServletUtils
{
    /**
     * Sends headers to allow a file to be download to the workstation vs.
     * opened in the browser.
     *
     * @param fileName
     *            the name of the file. This will be encoded as UTF-8.
     * @param contentLen
     *            the length of the file, zero (0) if unknown.
     * @param request
     *            the {@code HttpServletRequest}.
     * @param response
     *            the {@code HttpSerletResponse}.
     * @throws UnsupportedEncodingException
     */
    public static void sendHeaders(String fileName, int contentLen, HttpServletRequest request, HttpServletResponse response) throws UnsupportedEncodingException
    {
        String ua = request.getHeader("User-Agent").toLowerCase();
        boolean isIE = ((ua.indexOf("msie 6.0") != -1) || (ua.indexOf("msie 7.0") != -1)) ? true : false;
        String encName = URLEncoder.encode(fileName, "UTF-8");
        // Derived from Squirrel Mail and from
        // http://www.jspwiki.org/wiki/BugSSLAndIENoCacheBug
        if (request.isSecure())
        {
            response.addHeader("Pragma", "no-cache");
            response.addHeader("Expires", "-1");
            response.addHeader("Cache-Control", "no-cache");
        }
        else
        {
            response.addHeader("Cache-Control", "private");
            response.addHeader("Pragma", "public");
        }
        if (isIE)
        {
            response.addHeader("Content-Disposition", "attachment;filename=\"" + encName + "\"");
            response.addHeader("Connection", "close");
            response.setContentType("application/force-download;name=\"" + encName + "\"");
        }
        else
        {
            response.addHeader("Content-Disposition", "attachment;filename=\"" + encName + "\"");
            response.setContentType("application/octet-stream;name=\"" + encName + "\"");
            if (contentLen > 0)
                response.setContentLength(contentLen);
        }
    }
}

web.xml

<servlet>
    <servlet-name>CopyObjectServlet</servlet-name>
    <servlet-class>gwtsample.server.CopyObjectServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>CopyObjectServlet</servlet-name>
    <url-pattern>/gwtsample/copyObjectServlet</url-pattern>
</servlet-mapping>

ボタンのイベント処理：

sendButton.addClickHandler(new ClickHandler()
{
    @Override
    public void onClick(ClickEvent event)
    {
        String copyURL = GWT.getModuleBaseURL() +
        "copyObjectServlet?param0=";
        new DownloadIFrame(copyURL);
    }
});

ｈｔｍｌファイル：

<div id="__gwt_downloadFrame"></div>