我有一个java程序,它根据发送到该程序的参数生成有效的BufferedImage bi。我想从 servlet 调用该程序,并让 servlet 向用户发送一个包含适合用户输入参数的图像的 jsp。我在下面编写的代码生成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问题。
谁能告诉我如何更改下面的代码,以便它在用户的网络浏览器中输出实际图像而不是空消息?
这是 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:
<小时/>我已经根据我对Joop建议的理解编辑了我的代码,但它仍然不起作用。您能告诉我如何进一步编辑它以使其正常工作吗?
这是 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;
}
}
这是 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{}
}
这是 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>
最佳答案
您似乎有 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=... 发送 html-page-url
(使用 send-image-into-html.jsp(包含图像)进行响应)。
使用参数 imageParam1=... 获取 get-graph.gif
(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所在并一一解决。向 servlet 添加完整的日志记录,并使用 FireBug/Chrome DevTools 等工具来准确查看发生的情况。查看请求、参数和生成的 html。哪些网址是正确的?哪些参数是正确的?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。这个可以自己测试一下,直接在浏览器中输入url即可。检查您是否需要 .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());
}
当图像正确显示后,然后测试包含该图像的页面。您现在知道 url 应该是什么,因此请查看生成的 html 并将其与您期望的进行比较。图片源是否正确?
<td width=350>
<img src="<%="/get-graph.gif?imageParam1="%>">
</td>
这看起来像使用绝对路径和扩展名,不输出任何参数值,即使用户不输入 imageParam 也会显示。
所以这里需要输出 imageParam1 参数的值,可能在它周围有一个 if 语句。您现在可以像在其他地方一样使用 scriplet,但您应该考虑使用 jSTL 等标签库。
编辑:
我没有 GetBI 类,但我测试了这个示例:
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());
}
}
这会显示一个图像,其中 imageParam1 的文本位于:
http://127.0.0.1:8080/myapp/get-graph?imageParam1=Testing
关于java - 图像文件未从 servlet 加载到 JSP 中,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/18026535/