從jsp調用servlet並返回jsp

Question

我試圖從jsp訪問servlet，然後使用webservice訪問代碼（如果數組列表傳遞爲0）。它應顯示圖像，如果它傳遞1，它應該顯示不同的jsp。我能夠生成代碼，但不能按預期工作。任何人都可以找出問題所在。

package sal;

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，您的代碼將無法工作，因爲你到writeImageToBuffer呼叫已被註釋掉，並在doGet(req,resp)你的if/else語句總是調用dispatchToShowJsp()方法。

無論如何，使用Apache Commons IO幫助一些繁忙的工作中，你可以調用sendImageToResponse下面的方法來發送你的形象了：

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); 
      } 
     } 
    } 
}