java - 从jsp调用servlet并返回jsp

Question

我尝试从 jsp 访问 servlet，然后如果数组列表传递为 0，则使用 Web 服务访问代码。它应该显示图像，如果传递为 1，则应该显示不同的 jsp。我能够生成代码，但它没有按预期工作。任何人都可以弄清楚问题出在哪里。

封装萨尔；

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.List;

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

/**
 * Servlet implementation class Amberalerts
 */
public class Amberalerts extends HttpServlet {
    private static final long serialVersionUID = 1L;


    public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {

        List  list = getList();
        if(list != null && list.size() != 0){
          dispatchToShowJsp(req, resp, "/ShowImage.jsp");
        }else{
            dispatchToShowJsp(req, resp, "/ShowDefaultMsg.jsp");
        }

        // writeImageTOBuffer(resp);
    }
    private List getList() {
        List<String> list = new ArrayList<String>();
        list.add("Result");
        return list;
    }
    private void dispatchToShowJsp(HttpServletRequest req,
            HttpServletResponse resp, String jsplocation) throws IOException {
        try {
            getServletConfig().getServletContext().getRequestDispatcher(
                    jsplocation).forward(req,resp);
        } catch (ServletException e) {

            e.printStackTrace();
        }
    }
    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */


    private void writeImageTOBuffer(HttpServletResponse resp)
            throws FileNotFoundException, IOException {
        // Get the absolute path of the image
        ServletContext sc = getServletContext();
        String filename = sc.getRealPath("rsc/image.gif");

        // Get the MIME type of the image
        String mimeType = sc.getMimeType(filename);
        if (mimeType == null) {
            sc.log("Could not get MIME type of "+filename);
            resp.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
            return;
        }

        // Set content type
        resp.setContentType(mimeType);

        // Set content size
        File file = new File(filename);
        resp.setContentLength((int)file.length());

        // Open the file and output streams
        FileInputStream in = new FileInputStream(file);
        OutputStream out = resp.getOutputStream();

        // Copy the contents of the file to the output stream
        byte[] buf = new byte[1024];
        int count = 0;
        while ((count = in.read(buf)) >= 0) {
            out.write(buf, 0, count);
        }
        in.close();
        out.close();
    }


    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
    }

}

Answer 1

值得注意的是，您的代码将无法工作，因为您对 writeImageToBuffer 的调用已被注释掉，并且 doGet(req,resp) 中的 if/else 语句将始终调用 dispatchToShowJsp() 方法。

无论如何，使用 Apache Commons IO为了帮助一些繁忙的工作，您可以调用下面的sendImageToResponse方法来发送您的图像:

package com.stackoverflow.servlet;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

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

import org.apache.commons.io.FileUtils;
import org.apache.commons.io.IOUtils;

public class ShowImageServlet extends HttpServlet {

        public void sendImageToResponse(HttpServletResponse response) throws ServletException, IOException {

        File imageFile = new File("PATH_TO_YOUR_IMAGE_FILE"); // configure this however you want

        OutputStream outStream = null;
        InputStream inStream = null;

        try {

            outStream = response.getOutputStream();

            // Open image file
            inStream = FileUtils.openInputStream(imageFile);

            response.setContentType("image/jpeg");

            System.out.println("SENDING " + imageFile);

            // Send image file
            IOUtils.copy(inStream, outStream);

            System.out.println("SENT SIZE=" + imageFile.length());

        } catch (Exception ex) {

            // Handle your exception

        } finally {

            // close image file
            IOUtils.closeQuietly(inStream);

            try {

                // flush stream
                outStream.flush();

            } catch (Exception ignore) {

                // Ignore

            } finally {

                IOUtils.closeQuietly(outStream);
            }
        }
    }
}