【Java.Web】Servlet —— 实例 之 动态生成图像
动态生成图像
在这个例子中，我们首先通过一个Servlet（ImageServlet）动态的生成一个图像，然后在另一个Servlet（ShowImageServlet）中通过设置<image>元素的src属性指向这个Servlet来动态地生成图像：
创建第一个Servlet用于生成图像，可以通过如下的url指定图像显示的文本内容：
http://localhost:8080/base-webapp/image?text=my image servlet
package com.gof.test.servlet;
import java.io.IOException;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import com.sun.image.codec.jpeg.JPEGImageEncoder;
import com.sun.image.codec.jpeg.JPEGCodec;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.ServletOutputStream;
public class ImageServlet extends HttpServlet {
/**
*
*/
private static final long serialVersionUID = 6311783263824452228L;
private Font font = new Font("Courier", Font.BOLD,12);
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException{
String text = req.getParameter("text");
if(text == null){
text = "DEMO";
}
int len = text.length();
resp.setContentType("image/jpeg");
ServletOutputStream out = resp.getOutputStream();
BufferedImage image = new BufferedImage(11*len, 16, BufferedImage.TYPE_INT_RGB);
Graphics g = image.getGraphics();
g.setColor(Color.black);
g.fillRect(0, 0, 11*len, 16);
g.setColor(Color.white);
g.setFont(font);
char c;
for (int i = 0; i < len; i++){
c = text.charAt(i);
g.drawString(c + " ", i*11, 12);
}
JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
encoder.encode(image);
out.close();
}
}<span style="font-family:SimSun;font-size:10px;">
</span>
通过浏览器访问上面的URL:
下面创建第二个Servlet用于显示图像，其中图像通过在html正文中指定image的src属性，使其指向上面的servlet：
package com.gof.test.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ShowImageServlet extends HttpServlet {
/**
*
*/
private static final long serialVersionUID = -6345607864598566037L;
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException{
resp.setContentType("text/html;charset=utf-8");
PrintWriter out = resp.getWriter();
out.println("<html><head><title>Show Image</title></head>");
out.println("<body>");
String imageLink = "<img src='image?text=testing string'/>";
out.println("The image is: " + imageLink);
out.println("</body></html>");
out.close();
}
}
通过浏览器访问上面的Servlet：
http://localhost:8080/base-webapp/showimage
可以看到浏览器在遇到<image>元素的时候，再次发出一个http request请求第一个servlet - image；通过两次http request完成上面页面的加载。
配置servlet在web.xml：
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<display-name>Base Java Webapp</display-name>
<description>A Basic Maven Java Webapp Application</description>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<!-- test url: http://localhost:8080/base-webapp/download?filename=testreport.txt -->
<servlet>
<servlet-name>downloadtest</servlet-name>
<servlet-class>com.gof.test.servlet.DownloadServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>downloadtest</servlet-name>
<url-pattern>/download</url-pattern>
</servlet-mapping>
<!-- test upload file: http://localhost:8080/base-webapp/uploadfile.html -->
<servlet>
<servlet-name>uploadfiletest</servlet-name>
<servlet-class>com.gof.test.servlet.UploadFileServlet</servlet-class>
<init-param>
<param-name>filePath</param-name>
<param-value>/upload</param-value>
</init-param>
<init-param>
<param-name>tempFilePath</param-name>
<param-value>/tempupload</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>uploadfiletest</servlet-name>
<url-pattern>/uploadfile</url-pattern>
</servlet-mapping>
<!-- Image Servlet -->
<!-- access to this servlet through url: i.e. http://localhost:8080/base-webapp/image?text=123 -->
<servlet>
<servlet-name>image</servlet-name>
<servlet-class>com.gof.test.servlet.ImageServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>image</servlet-name>
<url-pattern>/image</url-pattern>
</servlet-mapping>
<!-- Show Image Servlet -->
<!-- access to this servlet through url: i.e. http://localhost:8080/base-webapp/showimage -->
<servlet>
<servlet-name>showimage</servlet-name>
<servlet-class>com.gof.test.servlet.ShowImageServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>showimage</servlet-name>
<url-pattern>/showimage</url-pattern>
</servlet-mapping>
</web-app>