圖像文件未從servlet中加載到JSP中
[英]image file not loading in JSP from servlet
問題描述
我有一個java程序，它根據發送到程序的參數生成有效的BufferedImage bi。 我想從servlet調用這個程序，並讓servlet向用戶發送一個包含符合用戶輸入參數的圖像的jsp。 我在下面寫的代碼生成一個空消息而不是請求的圖像。
我應該補充一點，get_bi（）有時需要幾百毫秒才能在我的開發計算機上生成BufferedImage。 不確定問題的一部分是否是時間延遲的事情。
任何人都可以告訴我如何更改下面的代碼，以便它在用戶的Web瀏覽器中輸出實際圖像而不是空消息？
這是ImageServlet的代碼：
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的代碼是：
<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" %>
編輯：
我根據我對Joop建議的理解編輯了我的代碼，但它仍然不起作用。 你能告訴我如何進一步編輯它以使其有效嗎？
這是FirstServlet的代碼：
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;
}
}
這是SecondServlet的代碼：
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{}
}
這是send-image-into-html.jsp的代碼
<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中的相關標記：
<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>
3 個解決方案
解決方案1
1 2013-08-02 22:05:59
使用帶有getRealPath文件轉換的Web應用程序路徑。
File imgFile = req.getServletContext().getRealPath("/images/generated.gif");
<img src="/images/generated.gif?t=<%= imgFile.lastModified() %>">
添加偽參數t=...以防止緩存。
由於重定向（對HTML！）不是這樣的：
//resp.setContentType("image/gif");
//resp.setContentLength((int)imgFile.length());
您也可以在img.src中輸入servlet URL，以便在沒有文件的情況下即時生成圖像：
resp.setContentType("image/gif");
ImageIO.write(bi, "gif", resp.getOutputStream());
創建一個單獨的圖像生成servlet，在響應的輸出流上返回圖像的二進制數據。 <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());
}
解決方案2
1 已采納 2013-08-04 11:32:14
看起來您有3個單獨的請求：
獲取html-page-url
（用send-image-into-html.jsp（包含表格）回復）。
POST html-page-url，參數imageParam1 = ...
（用send-image-into-html.jsp（包含圖像）回復）。
使用參數imageParam1 = G獲取get-graph.gif
（使用gif內容類型和圖像數據進行響應）。
重要的是縮小問題所在並逐一解決。 將完整日志記錄添加到servlet並使用FireBug / Chrome DevTools之類的工具來查看正在發生的事情。 查看請求，參數和生成的html。 哪些網址正確？ 哪些參數正確？ 哪些回答是正確的？
我認為第一個要求是正常工作。
從第三個請求開始。 這可以通過直接在瀏覽器中輸入URL來自行測試。 檢查是否需要.gif擴展名和完整路徑。
您至少需要刪除重復的行和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());
}
正確顯示圖像后，請測試包含圖像的頁面。 你現在知道了url應該是什么，所以看看生成的html並將它與你期望的進行比較。 圖像src是否正確？
<td width=350>
<img src="<%="/get-graph.gif?imageParam1="%>">
</td>
這看起來像使用絕對路徑和擴展名，不輸出任何參數值，即使用戶沒有輸入imageParam也會顯示。
因此，需要在此處輸出imageParam1參數的值，可能在其周圍使用if語句。 您現在可以像在其他地方一樣使用scriplet，但是您應該考慮使用像jstl這樣的標記庫。
編輯：
我沒有GetBI類，但我測試了這個例子：
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());
}
}
這將顯示imageParam1文本的圖像：
http://127.0.0.1:8080/myapp/get-graph?imageParam1=Testing
解決方案3
0 2013-08-03 12:41:40
試試這個......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;
}
}
將圖片從servlet加載到JSP
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