Web基础-05 HttpServletResponse

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HttpServletResponse

  web服务器接收到客户端的http请求,针对这个请求,分别创建一个代表请求的HttpServletReques对象,一个代表响应的HttpServletResponser对象

   1、如果要获取客户端请求过来的参数:找HttpServletRequest

   2、如果要给客户端响应一些信息:找HttpServletResponse

1、简单分类

  负责向浏览器发送数据的方法

ServletOutputStream getOutputStream() throws IOException;
PrintWriter getWriter() throws IOException;

  负责向浏览器发送响应头的方法

void 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)

  响应的状态码

技术图片
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;
nt 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;
View Code

2、下载文件

1、像浏览器输出消息

2、下载文件

  1、要获取下载文件的路径

  2、下载文件的下载名是啥?

  3、设置想办法让浏览器能够支持下载我们需要的东西

  4、获取下载文件的输入流

  5、创建缓冲区

  6、获取OutputStream对象

  7、将FileOutputStream流写入到buffer缓冲区

  8、使用OutputStream见缓冲区中数据输出到客户端!

public class FileServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {


// 1. 要获取下载文件的路径

        String realPath = "D:\\JavaStudy\\JavaWeb\\javaweb-02-servlet\\response\\target\\classes\\游戏.png";
        System.out.println("下载文件的路径:"+realPath);
// 2. 下载的文件名是啥?
        String fileName = realPath.substring(realPath.lastIndexOf("\\") + 1);//截取最后一个//后的内容
// 3. 设置想办法让浏览器能够支持(Content-Disposition) 下载我们需要的东西 ,中文文件名 +URLEncoder.encode编码,否者有可能乱码
        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);//通过realPath获取文件并返回一个InputStream流

// 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);

        }
// 8. 关闭流

        in.close();
        out.close();
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

 在web.xml注册对应的FileServlet

<servlet>
    <servlet-name>filedown</servlet-name>
    <servlet-class>com.pao.servlet.FileServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>filedown</servlet-name>
    <url-pattern>/down</url-pattern>
  </servlet-mapping>

  3、验证码功能

  验证怎么来的?

  前端实现

  后端实现,需要用到java的图片类,生产一个图片

public class ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //如何让浏览器5秒刷新一次
        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);
        //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");

        //把图片写给浏览器
        ImageIO.write(image,"jpg", resp.getOutputStream());
    }
    //生成随机数的方法
    private String makeNum(){
        Random random = new Random();
        String num = random.nextInt(99999999) + "";
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < 7-num.length(); i++) {

            sb.append(0);
        }
        String s = sb.toString() + num;
        return num;

    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

  组测servlet

<servlet>
    <servlet-name>ImageServlet</servlet-name>
    <servlet-class>com.pao.servlet.ImageServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>ImageServlet</servlet-name>
    <url-pattern>/img</url-pattern>
  </servlet-mapping>

4、实现重定向

技术图片

 

重定向流程: 一个web资源B,收到客户端A的请求后,B会通知A客户端去访问另外一个Web资源C,这样的一个请求过程叫做重定向

常见场景:

  用户登陆

void sendRedirect(String var1) throws IOException;

  重定向测试:

  

public class RedirectServlet  extends HttpServlet {

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

resp.sendRedirect("/img");//用户请求/red会自定转发到/img下

}

@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}


web.xml 注册servlet
<servlet>
<servlet-name>RedirectServlet</servlet-name>
<servlet-class>com.pao.servlet.RedirectServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>RedirectServlet</servlet-name>
<url-pattern>/red</url-pattern>
</servlet-mapping>


  面试题:请你聊一下重定向和转发的去区别?

  相同点:    页面都会跳转

  不同点:

    请求转发的时候,url不会发生变化

    重定向的时候,url地址栏会发生变化

  简单实现登陆重定向

  index.jsp

<html>
<body>
<h2>Hello World!</h2>
<%--这里提交的路径,需要寻找到项目的路径--%>
<%--pageContext.request.contextPath  代表当前的项目--%>
<form action="${pageContext.request.contextPath}/login" method="get">
        用户名:<input type="text" name="username">
        密码:<input type="password" name="password">
        <input type="submit">
</form>


</body>
</html>

  

public class RequestTest extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //处理请求
        String username = req.getParameter("username");
        String password = req.getParameter("password");

        System.out.println(username + ":" + password);

        //重定向的时候一定要注意,路径问题,否者404
        resp.sendRedirect("/success.jsp");


    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

  注册servlet

<servlet>
    <servlet-name>RequestTest</servlet-name>
    <servlet-class>com.pao.servlet.RequestTest</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>RequestTest</servlet-name>
    <url-pattern>/login</url-pattern>
  </servlet-mapping>

  测试的流程:用户点击提交按钮,发出一个/login的请求,请求响应到RequestTest ,在这里对前端发来的请求进行处理,并通过重定向将请求转发到”/success.jsp“,最后在前端显示出来

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