HttpServletResponse对象代表服务器的响应。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。
1、负责向客户端(浏览器)发送数据的方法:
ServletOutputStream getOutputStream() throws IOException;
PrintWriter getWriter() throws IOException;
2、负责向客户端(浏览器)发送响应头的方法：
oid setCharacterEncoding(String var1);
void setContentLength(int var1);
void setContentLengthLong(long var1);
void setContentType(String var1);
void setDateHeader(String var1, long var2);
void addDateHeader(String var1, long var2);
void setHeader(String var1, String var2);
void addHeader(String var1, String var2);
void setIntHeader(String var1, int var2);
void addIntHeader(String var1, int var2);
3、负责向客户端(浏览器)发送响应状态码的方法：
void setStatus(int var1);
4、响应的状态码（常量）：
int SC_CONTINUE = 100;
int SC_SWITCHING_PROTOCOLS = 101;
int SC_OK = 200;
int SC_CREATED = 201;
int SC_ACCEPTED = 202;
int SC_NON_AUTHORITATIVE_INFORMATION = 203;
int SC_NO_CONTENT = 204;
int SC_RESET_CONTENT = 205;
int SC_PARTIAL_CONTENT = 206;
int SC_MULTIPLE_CHOICES = 300;
int SC_MOVED_PERMANENTLY = 301;
int SC_MOVED_TEMPORARILY = 302;
int SC_FOUND = 302;
int SC_SEE_OTHER = 303;
int SC_NOT_MODIFIED = 304;
int SC_USE_PROXY = 305;
int SC_TEMPORARY_REDIRECT = 307;
int SC_BAD_REQUEST = 400;
int SC_UNAUTHORIZED = 401;
int SC_PAYMENT_REQUIRED = 402;
int SC_FORBIDDEN = 403;
int SC_NOT_FOUND = 404;
int SC_METHOD_NOT_ALLOWED = 405;
int SC_NOT_ACCEPTABLE = 406;
int SC_PROXY_AUTHENTICATION_REQUIRED = 407;
int SC_REQUEST_TIMEOUT = 408;
int SC_CONFLICT = 409;
int SC_GONE = 410;
int SC_LENGTH_REQUIRED = 411;
int SC_PRECONDITION_FAILED = 412;
int SC_REQUEST_ENTITY_TOO_LARGE = 413;
int SC_REQUEST_URI_TOO_LONG = 414;
int SC_UNSUPPORTED_MEDIA_TYPE = 415;
int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;
int SC_EXPECTATION_FAILED = 417;
int SC_INTERNAL_SERVER_ERROR = 500;
int SC_NOT_IMPLEMENTED = 501;
int SC_BAD_GATEWAY = 502;
int SC_SERVICE_UNAVAILABLE = 503;
int SC_GATEWAY_TIMEOUT = 504;
int SC_HTTP_VERSION_NOT_SUPPORTED = 505;
5、应用：
- 向浏览器发送数据：getWriter()、getOutputStream()；
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
@WebServlet("/hello")
public class HelloServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.setContentType("text/html");
resp.setCharacterEncoding("utf-8");
PrintWriter writer = resp.getWriter();
writer.print("<h1>HelloServlet</h1>");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req,resp);
}
}
运行结果如下：
- 下载文件：
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.URLEncoder;
@WebServlet("/down")
public class FileServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
//1、获取下载文件的路径
//String realpath = this.getServletContext().getRealPath("xxx"); //获取要下载的文件的绝对路径
String realpath = "D:\Users\Java\JavaWeb\Servlet\Servlet-03-Response\target\classes\白豆五.png";
System.out.println("下载文件的路径:" + realpath);
//2、获取文件名
String fileName = realpath.substring(realpath.lastIndexOf("\") + 1);
//3、设置content-disposition响应头控制浏览器以下载的形式打开文件,使用URLEncoder.encode解决文件名乱码问题
resp.setHeader("Content-disposition", "attachment;filename=" + URLEncoder.encode(fileName, "UTF-8"));
//4、获取下载文件的输入流；
FileInputStream in = new FileInputStream(realpath);
//5、创建缓冲区
int len = 0;
byte[] buffer = new byte[1024];
//6、获取OutputStream对象；
ServletOutputStream out = resp.getOutputStream();
//7、将FileOutputStream流写入到buffer缓冲区,使用OutputStream将缓冲区中的数据输出到客户端。
while ((len = in.read(buffer)) > 0) {
out.write(buffer, 0, len);
}
in.close();
out.close();
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
运行结果如下：
- 实现验证码功能：
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;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;
@WebServlet("/checkcode")
public class ImageServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//让浏览器3秒自动刷新一次
resp.setHeader("refresh", "3");
//在内存中创建一个图片
BufferedImage image = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);
//得到图片
Graphics2D g = (Graphics2D) image.getGraphics(); //笔
//设置图片的背景颜色
g.setColor(Color.white);
g.fillRect(0, 0, 80, 20);//矩形
//给图片写数据
g.setColor(Color.blue);
g.setFont(new Font(null, Font.BOLD, 20));
g.drawString(makeNum(), 0, 20);
//告诉浏览器，这个请求用图片的方式打开
resp.setContentType("image/jpeg");
//网站存在缓存，不让浏览器缓存
resp.setDateHeader("expires", -1);
resp.setHeader("Cache-Control", "no-cache");
resp.setHeader("Pragma", "no-cache");
//把图片输出给浏览器
ImageIO.write(image, "jpeg", resp.getOutputStream());
}
/**
* 生成随机数
*
* @return
*/
private String makeNum() {
Random random = new Random();
//String.valueOf(random.nextInt(9999));
String num = random.nextInt(9999999) + "";
StringBuffer sb = new StringBuffer();
for (int i = 0; i < 7 - num.length(); i++) {
sb.append("0");
}
num = sb.toString() + num;
return num;
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
运行结果如下：
