我有一个java程序，它根据发送给程序的参数生成有效的BufferedImage bi。我想从servlet调用这个程序，并让servlet向用户发送一个包含符合用户输入参数的图像的jsp。我在下面写的代码生成一个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BufferedImage。不确定问题的一部分是否是时间延迟的事情。
任何人都可以告诉我如何更改下面的代码，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;
}
}
send-image-into-html.jsp的代码是：
<jsp:useBean id="errors" scope="request" type="java.util.Map" class="java.util.HashMap" />
<%@ include file="top.inc" %>
<%@ include file="middle.inc" %>
<table>
<tr>
<td width=350>
<%=request.getParameter("imgFile")%>
<img src="<%=request.getParameter("imgFile")%>">
</td>
<td>
<form method="post">
<table>
<tr>
<td>Image Parameters: </td>
<td><input type="text" name="imageParams" value="some parameters" size="50" />
<% if (errors.containsKey("imageParams")) {
out.println("<span class=\"error\">" + errors.get("imageParams") + "</span>");
}%>
</td>
</tr>
<tr>
<td>
<input type="submit" name="submit-button" value="Click Here" />
</td>
</tr>
</table>
</form>
</td>
</tr>
</table>
<%@ include file="bottom.inc" %>
编辑：
我根据我对Joop建议的理解编辑了我的代码，但它仍然无效。你能告诉我如何进一步编辑它以使其有效吗？
以下是FirstServlet的代码：
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;
}
}
以下是SecondServlet的代码：
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{}
}
以下是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" %>
以下是web.xml中的相关标签：
<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>
答案 0 :(得分：1)
使用getRealPath进行文件转换的Web应用程序路径。
File imgFile = req.getServletContext().getRealPath("/images/generated.gif");
<img src="/images/generated.gif?t=<%= imgFile.lastModified() %>">
添加虚拟参数t=...以防止缓存。
由于重定向（对HTML！）而不是：
//resp.setContentType("image/gif");
//resp.setContentLength((int)imgFile.length());
你也可以在img.src中输入servlet URL，以便在没有文件的情况下即时生成图像：
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。 <img src="...?imageParam1=...&">的src URL映射在此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());
}
答案 1 :(得分：1)
看起来您有3个单独的请求：
获取html-page-url
（以send-image-into-html.jsp（包含表格）回复）。
使用参数imageParam1 = ...
发布html-page-url（用send-image-into-html.jsp（包含图片）回复）。
使用参数imageParam1 = ...
获取get-graph.gif（用gif内容类型和图像数据回复）。
重要的是缩小问题所在并逐一解决。将完整日志记录添加到servlet并使用FireBug / Chrome DevTools之类的工具来查看正在发生的事情。查看请求，参数和生成的html。哪些网址正确？哪些参数正确？哪些回答是正确的？
我认为第一个请求工作正常。
从第三个请求开始。这可以通过直接在浏览器中输入URL来自行测试。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());
}
正确显示图像后，请测试包含图像的页面。你现在知道了url应该是什么，所以看看生成的html并将它与你期望的进行比较。图像src是否正确？
<td width=350>
<img src="<%="/get-graph.gif?imageParam1="%>">
</td>
看起来它使用绝对路径和扩展名，不输出任何参数值，即使用户没有输入imageParam也会显示。
因此需要在此处输出imageParam1参数的值，可能在其周围使用if语句。您现在可以像在其他地方一样使用scriplet，但是您应该考虑使用像jstl这样的标记库。
修改
我没有GetBI类，但我测试了这个例子：
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());
}
}
这将显示imageParam1文本的图像：
http://127.0.0.1:8080/myapp/get-graph?imageParam1=Testing
答案 2 :(得分：0)
试试这个......它可以100％运行
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;
}
}