HttpServletResponse的应用
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getOutputStream与getWriter方法
.getOutputStream方法用于返回Servlet引擎创建的字节输出流对象,Servlet程序可以按字节形式输出响应正文。
.getWriter方法用于返回Servlet引擎创建的字符输出流对象,Servlet程序可以按字符形式输出响应正文。
.getOutputStream和getWriter这两个方法互相排斥,调用了其中的任何一个方法后,就不能再调用另一方法。
.getOutputStream方法返回的字节输出流对象的类型为ServletOutputStream,它可以直接输出字节数组中的二进制数据。
.getWriter方法将Servlet引擎的数据缓冲区包装成PrintWriter类型的字符输出流对象后返回,PrintWriter对象可以直接输出字符文本内容。
.Servlet程序向ServletOutputStream或PrintWriter对象中写入的数据将被Servlet引擎获取,Servlet引擎将这些数据当作响应消息的正文,然后再与响应状态行和各响应头组合后输出到客户端。
.Serlvet的service方法结束后,Servlet引擎将检查getWriter或getOutputStream方法返回的输出流对象是否已经调用过close方法,如果没有,Servlet引擎将调用close方法关闭该输出流对象。
选择getOutputStream 和getWriter方法的要点
.PrintWriter对象输出字符文本内容时,它内部还是将字符串转换成了某种字符集编码的字节数组后再进行输出,使用PrintWriter对象的好处就是不用编程人员自己来完成字符串到字节数组的转换。
.使用ServletOutputStream对象也能输出内容全为文本字符的网页文档,但是,如果网页文档内容是在Servlet程序内部使用文本字符串动态拼凑和创建出来的,则需要先将字符文本转换成字节数组后输出。
.如果一个网页文档内容全部为字符文本,但是这些内容可以直接从一个字节输入流中读取出来,然后再原封不动地输出到客户端,那么就应该使用ServletOutputStream对象直接进行输出,而不要使用PrintWriter对象进行输出。
HttpServletResponse实用例子
CacheTestServlet。java
package com.hbsi.csdn.ServletTest;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class CacheTestServlet extends HttpServlet {
/**
* Constructor of the object.
*/
public CacheTestServlet() {
super();
}
/**
* Destruction of the servlet. <br>
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}
/**
* The doGet method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
this.doPost(request, response);
}
/**
* The doPost method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=utf-8");
//禁止浏览器缓存当前的文档
response.setDateHeader("Expires", 0);
response.setHeader("Cache-Control", "no-Cache");
response.setHeader("Pragma", "no-Cache");
PrintWriter out = response.getWriter();
out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
out.println("<HTML>");
out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");
out.println(" <BODY>");
out.println("本次响应的随机数:"+Math.random());
//产生一个form表单
out.println("<form action='NoServlet' method='POST'>");
out.println("第一个参数:<input type='text' name='p1'><br/>");
out.println("第二个参数:<textarea name='p2'></textarea><br/>");
out.println("<input type='submit' value='提交'></form>");
out.println(" </BODY>");
out.println("</HTML>");
out.flush();
out.close();
}
/**
* Initialization of the servlet. <br>
*
* @throws ServletException if an error occurs
*/
public void init() throws ServletException {
// Put your code here
}
}
PageServlet.java
package com.hbsi.csdn.ServletTest;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class PageServlet extends HttpServlet {
/**
* Constructor of the object.
*/
public PageServlet() {
super();
}
/**
* Destruction of the servlet. <br>
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}
/**
* The doGet method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
this.doPost(request, response);
}
/**
* The doPost method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("application/x-msdownload"); //设置文件类型
response.addHeader("Content-Disposition", "attachment;filename=aa.txt");
ServletOutputStream sos=response.getOutputStream();
sos.write("this is a file".getBytes());
sos.close();
}
/**
* Initialization of the servlet. <br>
*
* @throws ServletException if an error occurs
*/
public void init() throws ServletException {
// Put your code here
}
}
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