一、简介
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.
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.
二、HttpServletResponse
HttpServletResponse对象,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.如下方法
三、HttpServletResponse常见应用
1、向客户端输出中文数据,注意字符流和字节流的区别,编码问题
例1：采用字节流
public class ServletTest extends HttpServlet {
protected void doGet(HttpServletRequest req, HttpServletResponse response)throws Exception {
test2(response);
}
private void test2(HttpServletResponse response) throws Exception {
String data="中国2";
//html: <meta>标签模拟一个http响应头,写回去后浏览器可以解析
OutputStream out=response.getOutputStream();
//out.write(data.getBytes()); //这种方式采用平台默认的字符集编码也就是gb2332
out.write("<meta http-equiv='content-type' content='text/html;charset=UTF-8'>".getBytes());
out.write(data.getBytes("UTF-8"));
}
//字节流可以读取任何数据,字符流只能读取字符
private void test1(HttpServletResponse response) throws Exception {
String data="中国";
//程序以什么码表输出,就要控制浏览器以什么码表打开(否则浏览器默认按平台的默认字符集进行解码输出)
response.setHeader("Content-type", "text/html;charset=UTF-8");
OutputStream out=response.getOutputStream();
//out.write(data.getBytes());使用平台的默认字符集将此 String 编码为 byte 序列
//下面这句程序会将data按UTF-8编码将数据转换为二进制数据传递给客户端
out.write(data.getBytes("UTF-8"));
}
}
例2：采用字符流
public class ResponseDemo2 extends HttpServlet { protected void doGet(HttpServletRequest req, HttpServletResponse response)throws Exception{ test1(response); } private void test2(HttpServletResponse response) throws IOException { String data="中国q"; //该句代码等价于其后面两句 response.setContentType("text/html;charset=UTF-8"); //response.setCharacterEncoding("UTF-8"); //response.setHeader("Content-type", "text/html;charset=UTF-8"); PrintWriter out=response.getWriter(); out.write(data);// } private void test1(HttpServletResponse response) throws IOException { String data="中国q"; //设置response使用的码表,控制以什么码表向response写入数据,默认为GBK字符集编码 response.setCharacterEncoding("UTF-8"); //指定浏览器以什么码表打开服务器发送的数据,默认为平台默认字符集编码 response.setHeader("Content-type", "text/html;charset=UTF-8"); PrintWriter out=response.getWriter(); out.write(data);//setCharacterEncoding就是控制这句写入response时的编码 } }
ps:建议都指明使用UTF-8字符集编码,这样比较清晰.
例3：如果要向客户端输出数据,要将数字变成字符串
public class ServletTest extends HttpServlet { protected void doGet(HttpServletRequest req, HttpServletResponse response) throws ServletException, IOException { test2(response); } private void test2(HttpServletResponse response) throws Exception { String data="1"; OutputStream out=response.getOutputStream(); out.write(data.getBytes()); } }
2、文件下载
//通过response实现文件下载 public class ResponseDemo3 extends HttpServlet { protected void doGet(HttpServletRequest req, HttpServletResponse response)throws Exception { test1(response); } private void test1(HttpServletResponse response) throws Exception { String path=this.getServletContext().getRealPath("/download/new.jpg"); //C:\apache-tomcat-7.0.22\webapps\day06\download\new.jsp String filename=path.substring(path.lastIndexOf("\\")+1);
//如果下载文件是中文文件,则文件名需要经过url编码 response.setHeader("content-disposition", "attachment;
filename="+URLEncoder.encode(filename,"UTF-8"));
//如下代码是一个模板 InputStream in=null; OutputStream out=null; try { in=new FileInputStream(path); int len=0; byte buffer[]=new byte[1024]; out=response.getOutputStream(); while((len=in.read(buffer))>0){ out.write(buffer,0,len); } }finally{ if(in!=null){ try{ in.close();//注意并没有关闭response流,交给servlet去管理 }catch(Exception e){ e.printStackTrace(); } } } } }
3、输出随机图片,防止恶意注册
package cn.itcast.response; import java.awt.Color; import java.awt.Graphics; import java.awt.image.BufferedImage; import java.util.Random; import javax.servlet.http.HttpServlet; public class RandomImage { private final static int WIDTH=80; private final static int HEIGHT=30; public static BufferedImage createImage(){ //创建图片 BufferedImage image=new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_BGR); //得到图形绘制的对象 Graphics g=image.getGraphics(); //设置背景颜色 setBackGroud(g); //设置边框 setBorder(g); //绘制内容 drawContent(g); //绘制干扰线 drawDisturbLine(g); return image; } /** * 绘制干扰线 * @param g */ private static void drawDisturbLine(Graphics g) { g.setColor(Color.yellow); Random r=new Random(); for(int i=0;i<4;i++){ int x1=r.nextInt(WIDTH); int y1=r.nextInt(HEIGHT); int x2=r.nextInt(WIDTH); int y2=r.nextInt(HEIGHT); g.drawLine(x1, y1, x2, y2); } } /** * 绘制内容 * @param g */ private static void drawContent(Graphics g) { //字符资源 String resource="\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\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"; //获取字符长度 int length=resource.length(); //随机操作对象 Random r=new Random(); //存储字符对象 StringBuffer sb=new StringBuffer(); for(int i=0;i<4;i++){ //随机产生数字 int index=r.nextInt(length); //获取字符 char c=resource.charAt(index); //拼接字符 sb.append(c); } g.setColor(Color.black); g.drawString(sb.toString(), 20, 20); } /** * 设置边框 * @param g */ private static void setBorder(Graphics g) { g.setColor(Color.black); g.drawRect(0, 0, WIDTH-2, HEIGHT-2); } /** * 设置背景颜色 * @param g */ private static void setBackGroud(Graphics g) { //绘制矩形 g.setColor(Color.lightGray); g.fillRect(0,0, WIDTH, HEIGHT); } } public class ImgServlet extends HttpServlet { final int WIDTH=80; final int HEIGH=30; public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //禁止浏览器缓存数据 response.setHeader("expires", "0"); response.setHeader("Cache-Control", "no-cache"); response.setHeader("Pragma", "no-cache"); //通知浏览器以图片的方式打开数据 response.setContentType("image/jpeg"); //把图片显示给浏览器 ImageIO.write(RandomImage.createImage(), "jpeg", response.getOutputStream()); } }