response常见应用（中文数据乱码解决，中文文件下载，随机图片等）

1.Web服务器收到客户端的http请求，会针对每一次请求，分别创建一个用于代表请求的request对象、和代表响应的response对象。

2.request和response对象即然代表请求和响应，那我们要获取客户机提交过来的数据，只需要找request对象就行了。要向客户机输出数据，只需要找response对象就行了。

3.HttpServletResponse对应服务器的响应。这个对象中封装了向客户端发送数据、发送响应头，发送响应状态码的方法。

4.向客户端输出中文数据

(1)用outputStream输出中文数据的问题

package cn.lsl.response;
import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

//用outputStream输出中文数据的问题
public class ResponseDemo1 extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
test4(response);
}

//输出gb2312的数据，没出现中文乱码问题
public void test1(HttpServletResponse response) throws IOException{
String data = "你好";
OutputStream out = response.getOutputStream();
out.write(data.getBytes());
}

//输出UTF-8的数据，有出现乱码问题，需要控制浏览器以UTF-8打开
public void test2(HttpServletResponse response) throws IOException{
response.setHeader("content-type", "text/html;charset=UTF-8");
String data = "你好";
OutputStream out = response.getOutputStream();
out.write(data.getBytes("UTF-8"));
}

//用<meta>模拟一个http响应头，控制浏览器以UTF-8打开数据
public void test3(HttpServletResponse response) throws IOException{
response.getOutputStream().write("<meta http-equiv='content-type' content='text/html;charset=UTF-8'>".getBytes());
String data = "你好";
OutputStream out = response.getOutputStream();
out.write(data.getBytes("UTF-8"));
}

//控制数字乱码的问题
public void test4(HttpServletResponse response) throws IOException{
response.getOutputStream().write((120+"").getBytes("UTF-8"));
}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request,response);
}

}

（2）用writer输出中文数据

package cn.lsl.response;
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;

//用writer输出中文数据
public class ResponseDemo2 extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
test2(response);
}
public void test1(HttpServletResponse response) throws IOException{
//更改response的码表，通知服务器用UTF-8码表去取response中的数据，然后写给客户机
response.setCharacterEncoding("UTF-8");
//通知浏览器以UTF-8码表打开回送的数据
//response.setHeader("content-type", "text/html;charset=UTF-8");
response.setContentType("text/html;charset=UTF-8");
String data = "你好";
PrintWriter writer = response.getWriter();
writer.write(data);
}

public void test2(HttpServletResponse response) throws IOException{
//调用了这句话，相当于把response.setCharacterEncoding("UTF-8");也设好了
response.setContentType("text/html;charset=UTF-8");
String data = "你好";
PrintWriter writer = response.getWriter();
writer.write(data);
}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request,response);
}
}

5.中文文件的下载

package cn.lsl.response;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.URLEncoder;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

//中文文件的下载
public class ResponseDemo3 extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//1.获取需要下载的文件
String path = this.getServletContext().getRealPath("/download/一直很安静.mp3");
String filename = path.substring(path.lastIndexOf("\\")+1);
//System.out.println(filename);
//2.通知浏览器以下载方式打开（下载的中文文件名必须要给过URL编码）
response.setHeader("content-disposition", "attachment;filename="+URLEncoder.encode(filename,"UTF-8"));
//3.向浏览器写出数据
FileInputStream in = null;
try{
OutputStream out = response.getOutputStream();
in = new FileInputStream(path);
byte buffer[] = new byte[1024];
int len = 0;
while((len=in.read(buffer))>0){
out.write(buffer,0,len);
}
}finally{
if(in!=null){
in.close();		//关闭流
}
}

}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request,response);
}

}

6.随机图片

package cn.lsl.response;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

//输出随机图片
public class ResponseDemo4 extends HttpServlet {

private static final int WIDTH = 120;
private static final int HEIGHT = 25;
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//1.在内存中创建一个图片
BufferedImage image = new BufferedImage(WIDTH,HEIGHT,BufferedImage.TYPE_INT_RGB);  //长、宽、图片类型
//2.得到图片
Graphics g = image.getGraphics();
//3.设置背景色
setBackground(g);
//4.设置图片边框
setBorder(g);
//5.设置图片干扰线
drawRandomLine(g);
//6.向图片上写数据
drawRandomData2(g);
//7.把图片写给客户机，再通知浏览器以图片方式打开数据，并且要通知浏览器不能缓存图片（若没设置，浏览器将会取缓存图片）
response.setHeader("Expires", "-1");
response.setHeader("Cache-Control", "no-cache");
response.setHeader("Pragma", "no-cache");
response.setContentType("image/jpeg");
ImageIO.write(image, "jpg", response.getOutputStream());
}

//随机数字
private void drawRandomData(Graphics g) {
// TODO Auto-generated method stub
StringBuffer sb = new StringBuffer();
for(int i=0;i<5;i++){
sb.append(new Random().nextInt(10)+ " ");
}
String randomData = sb.toString();

g.setColor(Color.RED);
g.setFont(new Font("宋体",Font.BOLD,20));
g.drawString(randomData, 10, 20);

}

//随机文字
private void drawRandomData2(Graphics g){
StringBuffer sb = new StringBuffer();
String base = "\u7684\u4e00\u4e86\u662f\u6211\u4e0d\u5728\u4eba\u4eec\u6709\u6765\u4ed6\u8fd9\u4e0a\u7740\u4e2a\u5730\u5230\u5927\u91cc

\u8bf4\u5c31\u53bb\u5b50\u5f97\u4e5f\u548c\u90a3\u8981\u4e0b\u770b\u5929\u65f6\u8fc7\u51fa\u5c0f\u4e48\u8d77\u4f60\u90fd\u628a\u597d\u8fd8\u591a\u6ca1\u4e3a

\u53c8\u53ef\u5bb6\u5b66\u53ea\u4ee5\u4e3b\u4f1a\u6837\u5e74\u60f3\u751f\u540c\u8001\u4e2d\u5341\u4ece\u81ea\u9762\u524d\u5934\u9053\u5b83\u540e

\u7136\u8d70\u5f88\u50cf\u89c1\u4e24\u7528\u5979\u56fd\u52a8\u8fdb\u6210\u56de\u4ec0\u8fb9\u4f5c\u5bf9\u5f00\u800c\u5df1\u4e9b\u73b0\u5c71\u6c11\u5019\u7ecf

\u53d1\u5de5\u5411\u4e8b\u547d\u7ed9\u957f\u6c34\u51e0\u4e49\u4e09\u58f0\u4e8e\u9ad8\u624b\u77e5\u7406\u773c\u5fd7\u70b9\u5fc3\u6218\u4e8c\u95ee\u4f46\u8eab

\u65b9\u5b9e\u5403\u505a\u53eb\u5f53\u4f4f\u542c\u9769\u6253\u5462\u771f\u5168\u624d\u56db\u5df2\u6240\u654c\u4e4b\u6700\u5149\u4ea7\u60c5\u8def\u5206\u603b

\u6761\u767d\u8bdd\u4e1c\u5e2d\u6b21\u4eb2\u5982\u88ab\u82b1\u53e3\u653e\u513f\u5e38\u6c14\u4e94\u7b2c\u4f7f\u5199\u519b\u5427\u6587\u8fd0\u518d\u679c\u600e\u5b9a

\u8bb8\u5feb\u660e\u884c\u56e0\u522b\u98de\u5916\u6811\u7269\u6d3b\u90e8\u95e8\u65e0\u5f80\u8239\u671b\u65b0\u5e26\u961f\u5148\u529b\u5b8c

\u5374\u7ad9\u4ee3\u5458\u673a\u66f4\u4e5d\u60a8\u6bcf\u98ce\u7ea7\u8ddf\u7b11\u554a\u5b69\u4e07\u5c11\u76f4\u610f\u591c\u6bd4\u9636\u8fde\u8f66\u91cd\u4fbf

\u6597\u9a6c\u54ea\u5316\u592a\u6307\u53d8\u793e\u4f3c\u58eb\u8005\u5e72\u77f3\u6ee1\u65e5\u51b3\u767e\u539f\u62ff\u7fa4\u7a76\u5404\u516d\u672c\u601d\u89e3\u7acb

\u6cb3\u6751\u516b\u96be\u65e9\u8bba\u5417\u6839\u5171\u8ba9\u76f8\u7814\u4eca\u5176\u4e66\u5750\u63a5\u5e94\u5173\u4fe1\u89c9\u6b65\u53cd

\u5904\u8bb0\u5c06\u5343\u627e\u4e89\u9886\u6216\u5e08\u7ed3\u5757\u8dd1\u8c01\u8349\u8d8a\u5b57\u52a0\u811a\u7d27\u7231\u7b49\u4e60\u9635\u6015\u6708\u9752\u534a

\u706b\u6cd5\u9898\u5efa\u8d76\u4f4d\u5531\u6d77\u4e03\u5973\u4efb\u4ef6\u611f\u51c6\u5f20\u56e2\u5c4b\u79bb\u8272\u8138\u7247\u79d1\u5012\u775b\u5229\u4e16\u521a

\u4e14\u7531\u9001\u5207\u661f\u5bfc\u665a\u8868\u591f\u6574\u8ba4\u54cd\u96ea\u6d41\u672a\u573a\u8be5\u5e76\u5e95\u6df1\u523b\u5e73\u4f1f\u5fd9\u63d0\u786e

\u8fd1\u4eae\u8f7b\u8bb2\u519c\u53e4\u9ed1\u544a\u754c\u62c9\u540d\u5440\u571f\u6e05\u9633\u7167\u529e\u53f2\u6539\u5386\u8f6c\u753b\u9020\u5634\u6b64\u6cbb

\u5317\u5fc5\u670d\u96e8\u7a7f\u5185\u8bc6\u9a8c\u4f20\u4e1a\u83dc\u722c\u7761\u5174\u5f62\u91cf\u54b1\u89c2\u82e6\u4f53\u4f17\u901a\u51b2\u5408\u7834\u53cb

\u5ea6\u672f\u996d\u516c\u65c1\
b15c
u623f\u6781\u5357\u67aa\u8bfb\u6c99\u5c81\u7ebf\u91ce\u575a\u7a7a\u6536\u7b97\u81f3\u653f\u57ce\u52b3\u843d\u94b1\u7279\u56f4\u5f1f

\u80dc\u6559\u70ed\u5c55\u5305\u6b4c\u7c7b\u6e10\u5f3a\u6570\u4e61\u547c\u6027\u97f3\u7b54\u54e5\u9645\u65e7\u795e\u5ea7\u7ae0\u5e2e\u5566\u53d7\u7cfb

\u4ee4\u8df3\u975e\u4f55\u725b\u53d6\u5165\u5cb8\u6562\u6389\u5ffd\u79cd\u88c5\u9876\u6025\u6797\u505c\u606f\u53e5\u533a\u8863\u822c\u62a5\u53f6\u538b

\u6162\u53d4\u80cc\u7ec6";
for(int i=0;i<4;i++){
int num = new Random().nextInt(base.length());
sb.append(base.charAt(num)+" ");
}
String randomData = sb.toString();
g.setColor(Color.RED);
g.setFont(new Font("宋体",Font.BOLD,20));
g.drawString(randomData, 0, 20);
}

private void drawRandomLine(Graphics g) {
// TODO Auto-generated method stub
g.setColor(Color.GREEN);
for(int i=0;i<5;i++){
int x1 = new Random().nextInt(WIDTH);
int y1 = new Random().nextInt(HEIGHT);
int x2 = new Random().nextInt(WIDTH);
int y2 = new Random().nextInt(HEIGHT);
g.drawLine(x1, y1, x2, y2);
}

}

private void setBorder(Graphics g) {
// TODO Auto-generated method stub
g.setColor(Color.BLUE);
g.drawRect(1, 1, WIDTH-2, HEIGHT-2);

}

private void setBackground(Graphics g) {
// TODO Auto-generated method stub
g.setColor(Color.WHITE);
g.fillRect(0, 0, WIDTH, HEIGHT);
}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request,response);
}

}

7.控制浏览器定时刷新网页

package cn.lsl.response;
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;

//控制网页定时刷新
public class ResponseDemo5 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String data = "中国的人";
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=UTF-8");
//response.setHeader("refresh", "3");
//用<meta>标签模拟
response.getWriter().write("<meta http-equiv='refresh' content='3;url=/Response/index.jsp'>");
response.getWriter().write(data);
}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
}
}

8.请求重定向

package cn.lsl.response;
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;
//请求重定向
/*1.请求重定向下，浏览器向服务器发送了2次请求，request和response对象分别有两个
* 2.请求重定向下，浏览器的地址会发生变化
* 3.请求重定向要少用，它只适合用于一些特定的场景下例如登录（因为用户登录成功后，我们系统希望用户知道他到首页上去了）
*/
public class ResponseDemo extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
/*response.setStatus(302);
response.setHeader("location", "/Response/index.jsp");*/
response.sendRedirect("/Response/index.jsp");
}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request,response);
}
}

9.getOutputStream和getWriter方法冲突的问题

getOutputStream和getWriter方法分别用于得到输出二进制数据、输出文本数据的ServletOuputStream、Printwriter对象。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。 

package cn.lsl.response;
import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

//getOutputStream和getWriter方法冲突的问题
//出错：java.lang.IllegalStateException: getWriter() has already been called for this response
public class ResponseDemo6 extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
/*OutputStream out = response.getOutputStream();
this.getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
//出错，调用流不同，因为转到jsp页面，服务器会自动帮你调用getWriter();*/

PrintWriter writer = response.getWriter();
this.getServletContext().getRequestDispatcher("/servlet/ResponseDemo7").forward(request, response);
//getWriter() has already been called for this response
//出错，因为ResponseDemo6跟ResponseDemo7调用的流不同
}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request,response);
}
}

//getOutputStream() has already been called for this response
//任何数据都可以用字节流输出

ResponseDemo7.java

package cn.lsl.response;
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 ResponseDemo7 extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.getOutputStream();
}

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request,response);
}
}