Java 未从servlet在JSP中加载图像文件

我有一个java程序，它根据发送到程序的参数生成有效的BuffereImage bi。我想从servlet调用这个程序，让servlet向用户发送一个jsp，其中包含一个符合用户输入参数的图像。我在下面编写的代码生成一条空消息，而不是请求的图像

我应该补充一点，get_bi（）有时需要几百毫秒才能在我的开发计算机上生成BuffereImage。不确定问题的一部分是否是时间延迟

有人能告诉我如何修改下面的代码，以便它在用户的web浏览器中输出实际图像而不是空消息吗

以下是ImageServlet的代码：

import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import javax.imageio.ImageIO;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
//import org.apache.log4j.Logger;
import myownpackage.GetBI;

public class ImageServlet extends HttpServlet{
//   private Logger logger = Logger.getLogger(this.getClass());
   private RequestDispatcher jsp;

   public void init(ServletConfig config) throws ServletException {
      ServletContext context = config.getServletContext();
      jsp = context.getRequestDispatcher("/WEB-INF/jsp/send-image-into-html.jsp");
   }

   protected void doGet(HttpServletRequest req, HttpServletResponse resp) 
       throws ServletException, IOException {
    //      logger.debug("doGet()");
          String imageParams = req.getParameter("imageParams");
          jsp.forward(req, resp);
   }

   protected void doPost(HttpServletRequest req, HttpServletResponse resp) 
       throws ServletException, IOException{  
       Map<String, String> errors = validate(req);
       if (!errors.isEmpty()){
          //         logger.debug("validation errors");
          jsp.forward(req, resp);
       return;
       }

      resp.setContentType("image/gif");
      BufferedImage bi = new BufferedImage(300, 300, BufferedImage.TYPE_INT_RGB);
      GetBI fetchBI = new GetBI();
      bi = fetchBI.get_bi(req.getParameter("imageParams"));
      File imgFile = new File("imgFile");
      ImageIO.write(bi, "gif", imgFile);
      resp.sendRedirect("send-image-into-html");
   }  

   public static Map<String, String> validate(HttpServletRequest req){
   HashMap<String, String> errors = new HashMap<String, String>();
   req.setAttribute("errors", errors);
   String imageParams = req.getParameter("imageParams");
   if (imageParams == null || imageParams.trim().length() == 0){
      errors.put("imageParams", "imageParams required.");
   }
   return errors;
 }
}

public class FirstServlet extends HttpServlet{
    //   private Logger logger = Logger.getLogger(this.getClass());
    private RequestDispatcher jsp;

public void init(ServletConfig config) throws ServletException {
    ServletContext context = config.getServletContext();
    jsp = context.getRequestDispatcher("/WEB-INF/jsp/send-image-into-html.jsp");
}

protected void doGet(HttpServletRequest req, HttpServletResponse resp) 
throws ServletException, IOException {//      logger.debug("doGet()");
    jsp.forward(req, resp);
}

protected void doPost(HttpServletRequest req, HttpServletResponse resp) 
throws ServletException, IOException{
    Map<String, String> errors = validate(req);
    if (!errors.isEmpty()){//         logger.debug("validation errors");
        jsp.forward(req, resp);
        return;
    }
    resp.sendRedirect("/send-image-into-html");
}

public static Map<String, String> validate(HttpServletRequest req){
    HashMap<String, String> errors = new HashMap<String, String>();
    req.setAttribute("errors", errors);
    String imageParam1 = req.getParameter("imageParam1");
    if (imageParam1 == null || imageParam1.trim().length() == 0){  
        errors.put("imageParam1", "imageParam1 required.");
    }
    return errors;
}
}  

public class GetGraphServlet extends HttpServlet{
    //   private Logger logger = Logger.getLogger(this.getClass());
    private RequestDispatcher jsp;

public void init(ServletConfig config) throws ServletException {
    ServletContext context = config.getServletContext();
    jsp = context.getRequestDispatcher("/WEB-INF/jsp/send-image-into-html.jsp");
}

protected void doGet(HttpServletRequest req, HttpServletResponse resp) 
throws ServletException, IOException {//      logger.debug("doGet()");
    // Create the BufferedImage, using any parameters and
    // possibly the exact request URI:
    String requestURI = req.getRequestURI();
    String imageParam1 = req.getParameter("imageParam1");
    resp.setContentType("image/gif");//256 colors
    BufferedImage bi = new BufferedImage(300, 300, BufferedImage.TYPE_INT_RGB);
    GetBI fetchBI = new GetBI();
    bi = fetchBI.get_bi(req.getParameter(imageParam1));
    ImageIO.write(bi,"gif",resp.getOutputStream());
    resp.setContentType("image/gif"); // 256 colors.
    ImageIO.write(bi, "gif", resp.getOutputStream());
    jsp.forward(req, resp);
}

protected void doPost(HttpServletRequest req, HttpServletResponse resp) 
throws ServletException, IOException{}
}

下面是send-image-into-html.jsp的代码

<jsp:useBean id="errors" scope="request" type="java.util.Map" class="java.util.HashMap" />
<%@ include file="top.inc" %>
<%@ include file="middle.inc" %>
    <form method="post">
        <table>
            <tr>
                <td width=350>
                    <img src="<%="/get-graph.gif?imageParam1="%>">
                </td>
                <td>
                    <table>
                        <tr>
                            <td>imageParam1: </td>
                            <td><input type="text" name="imageParam1" value="samplevalue" size="50" />
                            <%if (errors.containsKey("imageParam1")) {
                                out.println("<span class=\"error\">" + errors.get("imageParam1") + "</span>");}%>
                            </td>
                        </tr>
                        <tr>
                            <td>
                                <input type="submit" name="submit-button" value="CreateImage"/>
                            </td>
                        </tr>
                    </table>
                </td>
            </tr>
        </table>
    </form>
<%@ include file="bottom.inc" %>  

">
imageParam1：

以下是web.xml中的相关标记：

    <servlet>
        <servlet-name>FirstServlet</servlet-name>
            <servlet-class>mypackage.FirstServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>FirstServlet</servlet-name>
            <url-pattern>/html-page-url</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>SecondServlet</servlet-name>
        <servlet-class>mypackage.SecondServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>SecondServlet</servlet-name>
        <url-pattern>/get-graph</url-pattern>
    </servlet-mapping>

第一个servlet
mypackage.FirstServlet
第一个servlet
/html页面url
第二个servlet
mypackage.SecondServlet
第二个servlet
/获取图形

通过

getRealPath

使用web应用程序路径到文件的转换

  File imgFile = req.getServletContext().getRealPath("/images/generated.gif");

  <img src="/images/generated.gif?t=<%= imgFile.lastModified() %>">

您也可以将servlet URL放入img.src中，以便在没有文件的情况下动态生成图像：

  resp.setContentType("image/gif");
  ImageIO.write(bi, "gif", resp.getOutputStream());

---

创建一个单独的图像生成servlet，该servlet在响应的输出流上返回图像的二进制数据。

的src URL映射到此servlet上

<img src=".../... .gif?imageParam1=...&imageParam2=...">

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

       // Create the BufferedImage, using any parameters and
       // possibly the exact request URI:
       String requestURI = req.getRequestURI();
       String imageParam1 = req.getParameter("imageParam1");
       String imageParam2 = req.getParameter("imageParam2");

       BufferedImage bi = ...

       resp.setContentType("image/gif"); // 256 colors.
       ImageIO.write(bi, "gif", resp.getOutputStream());
}

受保护的无效数据集（HttpServletRequest-req、HttpServletResponse-resp）
抛出ServletException、IOException{
//使用任何参数和
//可能是确切的请求URI：
字符串requestURI=req.getRequestURI（）；
字符串imageParam1=req.getParameter（“imageParam1”）；
字符串imageParam2=req.getParameter（“imageParam2”）；
BuffereImage bi=。。。
resp.setContentType（“image/gif”）；//256色。
write（bi，“gif”，resp.getOutputStream（））；
}

试试这个……它100%有效

import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Iterator;
import java.util.List;

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

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileItemFactory;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

/**
 *
 * @author kites
 */
public class FileUpload extends HttpServlet {

    File uploadFile;
    /**
     * Processes requests for both HTTP <code>GET</code> and <code>POST</code> methods.
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */

    long fileSize;


    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        try {

            boolean bb = upload(request);


        } finally {
            out.close();
        }
    }

    // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
    /**
     * Handles the HTTP <code>GET</code> method.
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }

    /**
     * Handles the HTTP <code>POST</code> method.
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }

    /**
     * Returns a short description of the servlet.
     * @return a String containing servlet description
     */
    @Override
    public String getServletInfo() {
        return "Short description";
    }// </editor-fold>

    private boolean upload(HttpServletRequest request) {
        boolean bool = false;

        try {
                    String fileName = "";

            boolean isMultipart = ServletFileUpload.isMultipartContent(request);
            if (isMultipart) {
                System.out.println("Inside fileupload.....");
                FileItemFactory factory = new DiskFileItemFactory();
                ServletFileUpload upload = new ServletFileUpload(factory);
                List items = upload.parseRequest(request);
                Iterator iterator = items.iterator();
                //  System.out.println("File content" + request.getParameter("f1"));
                while (iterator.hasNext()) {
                    FileItem item = (FileItem) iterator.next();
                    FileItem item1 = item;
                    System.out.println("Form field:::" + item.isFormField());

                    if (!item.isFormField()) {
                        fileName = item.getName();
                        fileSize = item.getSize();
                        File f = new File("C:\\"+fileName);
                        String filepath=f.getAbsolutePath();

                        System.out.println("fileName = " + fileName);
                        System.out.println("fileSize = " + fileSize);
                        if (!fileName.equals("")) {


                            item.write(filepath);


                        }
                    }


                }


            }


        } catch (Exception e) {
            e.printStackTrace();
        }
        return bool;
    }


}

---

看起来您有3个单独的请求：

获取html页面url

（使用send-image-into-html.jsp（包含表单）进行响应）

使用参数imageParam1=

（使用send-image-into-html.jsp（包含图像）进行响应）

获取带有参数imageParam1=

（使用gif内容类型和图像数据进行响应）

重要的是要缩小问题的范围并逐一解决。将完整日志添加到servlet中，并使用FireBug/Chrome DevTools等工具查看到底发生了什么。查看请求、参数和生成的html。哪些URL正确？哪些参数正确？哪些响应正确

我想第一个要求很好

从第三个请求开始。这可以通过直接在浏览器中输入url来测试。检查是否需要.gif扩展名和完整路径

您至少需要删除重复的行和jsp.forward：

protected void doGet(HttpServletRequest req, HttpServletResponse resp) 
throws ServletException, IOException {
    // Create the BufferedImage, using any parameters and
    // possibly the exact request URI:
    String requestURI = req.getRequestURI();
    String imageParam1 = req.getParameter("imageParam1");
    BufferedImage bi = new BufferedImage(300, 300, BufferedImage.TYPE_INT_RGB);
    GetBI fetchBI = new GetBI();
    bi = fetchBI.get_bi(req.getParameter(imageParam1));

    resp.setContentType("image/gif");//256 colors
    ImageIO.write(bi,"gif",resp.getOutputStream());
}

当图像正确显示时，然后测试包含图像的页面。您现在知道url应该是什么，因此请查看生成的html并将其与您期望的内容进行比较。图像src正确吗

<td width=350>
    <img src="<%="/get-graph.gif?imageParam1="%>">
</td>

这将在以下位置显示带有imageParam1文本的图像：

http://127.0.0.1:8080/myapp/get-graph?imageParam1=Testing

---

感谢您的帮助。+1。我希望动态生成映像，以避免应用程序的并发用户出现问题。在添加ImageIO.write（bi，“gif”，resp.getOutputStream（））时，您能否在我的代码中显示您给出的动态建议的确切上下文；在doPost中，servlet返回图像，而不是返回一个包含图像的html页面，如>，eclipse告诉我没有定义ImageIO。有什么建议吗？另外，我没有使用Spring和getServletContext（）需要Spring。你对基本Java/tomcat有什么建议吗？还是我安装Spring的唯一选择？我想你说的是创建第二个servlet只用于。但是我如何将imageParams的内容放入第二个servlet？你能给我看一下这方面的显式代码吗？足以让我完全理解吗？我已经扩展了编辑答案。

getServletContext（）

也是

ServletRequest

的一种方法，它也是接口

HttpServletRequest

的基本接口。因此不需要通过ServletConfig。一般来说，不需要像您那样将请求分派器存储在

init

中。谢谢您的帮助。我将在接下来的几小时内仔细查看rs并返回给您更多问题。再次感谢。我尝试在浏览器中加载myapp/get graph，但在执行几个类时，它给了我一个错误，表明imageParam1只有空值。然后我键入myapp/get graph？imageParam1=“aValidValue“它给了我相同的空指针错误，表明它没有收到imageParam1的值。你能给我看清楚的工作代码吗？我真的很紧张，我不确定我是否能理解这个时间框架，除非我看到工作代码。我测试了get_bi（string）函数，该函数没有从servlet接收imageParam1值。我从另一个程序中调用了get_bi（string），它工作正常，在

<td width=350>
    <img src="<%="/get-graph.gif?imageParam1="%>">
</td>

public class SecondServlet extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String imageParam1 = request.getParameter("imageParam1");

        BufferedImage bi = new BufferedImage(300, 300, BufferedImage.TYPE_INT_RGB);

        // Try replacing with:
        //GetBI fetchBI = new GetBI();
        //BufferedImage bi = fetchBI.get_bi(req.getParameter("imageParam1"));

        Graphics2D g = bi.createGraphics();
        g.setColor(new Color(255, 255, 255));
        g.drawString(imageParam1, 0, 150);
        g.dispose();

        response.setContentType("image/gif");
        ImageIO.write(bi, "gif", response.getOutputStream());
    }
}

http://127.0.0.1:8080/myapp/get-graph?imageParam1=Testing