java web基础 --- 图像加载Http请求-优快云博客

本文链接：https://blog.youkuaiyun.com/bolininahuaalex/article/details/50409523

本文探讨了Java Web应用程序中如何处理图像加载，通过分析myform.html和web.xml文件的内容，讲解了利用HTTP请求获取并显示图像的基础知识。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

图片加载

myform.html

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="content-type" content="text/html;charset=utf-8">
<title>Insert title here</title>
</head>
<body>
	<h1>点击加载图片</h1>
	<form action="helloWorld" method="POST">
		<input type="submit" value="加载图片"/>
	</form>
</body>
</html>

testImage.html

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="content-type" content="text/html;charset=utf-8">
<title>Insert title here</title>
</head>
<body>
	<h1>图像加载测试-from servlet</h1>
	<img src="helloImage">
</body>
</html>

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" metadata-complete="true" version="3.0">
  <description>
		 Hello World Servlet
	</description>
  <display-name>Hello World Servlet</display-name>
  <servlet>
    <servlet-name>helloWorld</servlet-name>
    <servlet-class>com.web1.hello.HelloWorldServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>helloWorld</servlet-name>
    <url-pattern>/helloWorld</url-pattern>
  </servlet-mapping>
  
  <servlet>
    <servlet-name>helloImage</servlet-name>
    <servlet-class>com.web1.hello.ImageServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>helloImage</servlet-name>
    <url-pattern>/helloImage</url-pattern>
  </servlet-mapping>
</web-app>

HelloWorldServlet.java

package com.web1.hello;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class HelloWorldServlet
 */
@WebServlet("/HelloWorldServlet")
public class HelloWorldServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
    private String message;
    /**
     * @see HttpServlet#HttpServlet()
     */
    public HelloWorldServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see Servlet#init(ServletConfig)
	 */
	public void init(ServletConfig config) throws ServletException {
		message = "Hello world, Servlet Example!";
		/*重写了Servlet的init方法后一定要记得调用父类的init方法，
		否则在service/doGet/doPost方法中
		使用getServletContext()方法获取ServletContext对象时
		就会出现java.lang.NullPointerException异常*/
		super.init(config);
	}

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		//最原始的页面跳转
		String formPage = "/pages/myform.html";
		RequestDispatcher dispatcher = getServletContext().getRequestDispatcher(formPage);
		dispatcher.forward(request, response);
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		String formPage = "/pages/testImage.html";
		RequestDispatcher dispatcher = getServletContext().getRequestDispatcher(formPage);
		dispatcher.forward(request, response);
	}

	@Override
	public void destroy() {
		// TODO Auto-generated method stub
		super.destroy();
	}

}

ImageServlet.java

package com.web1.hello;

import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.nio.Buffer;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class ImageServlet
 */
@WebServlet("/ImageServlet")
public class ImageServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public ImageServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

	@Override
	public void init() throws ServletException {
		// TODO Auto-generated method stub
		super.init();
	}

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		String realPath = this.getServletContext().getRealPath("/");
		System.out.println(realPath);
		
		BufferedImage image = new BufferedImage(400, 400, BufferedImage.TYPE_INT_ARGB);
		Graphics2D g2d = image.createGraphics();
		g2d.setColor(Color.CYAN);
		g2d.fillRect(0, 0, 400, 400);
		g2d.setColor(Color.RED);
		g2d.drawString("My First Image", 150, 200);
		
		response.setContentType("image/png");
		ByteArrayOutputStream byteOutPut = new ByteArrayOutputStream();
		ImageIO.write(image, "png", byteOutPut);
		byte[] byteArray = byteOutPut.toByteArray();
		response.setContentLength(byteArray.length);
		
		OutputStream output = response.getOutputStream();
		output.write(byteArray);
		output.close();
	}


}