4.Servlet的Response和Request

一.综述

• web服务器接受到客户端的HTTP请求，对于这个请求分别创建一个代表请求的对象HttpServletRequest和一个代表响应的对象HttpServletResponse。

  • 如果要获得客户端请求过来的参数：找HttpServletRequest

  • 如果要给客户端响应一些参数信息：找HttpServletResponse

二.HttpServletResponse

 1.简单分类

负责向浏览器发送数据的方法

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

负责向浏览器发送响应头的方法

public void setCharacterEncoding(String charset);
public void setContentLength(int len);
public void setContentLengthLong(long len);
public void setContentType(String type);
public void setBufferSize(int size);
public void setLocale(Locale loc);

public void setDateHeader(String name, long date);
public void addDateHeader(String name, long date);
public void setHeader(String name, String value);
public void addHeader(String name, String value);
public void setIntHeader(String name, int value);
public void addIntHeader(String name, int value);
public void setStatus(int sc);

 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;

2.常见应用

1. 向浏览器输出消息

2. 下载文件

   1. 获得要下载文件的路径和文件名

   2. 设置浏览器能够支持下载

   3. 获取下载文件的输入流

   4. 创建缓冲区

   5. 获取OutputStream对象

   6. 将FileOutputStream流写入到buffer缓冲区中

   7. 使用OutputStream将缓冲区中的数据输出到客户端

3. 验证码功能

4. 实现重定向：使用场景用户登陆

注：

• 重定向的 / 表示：http://服务器ip:端口/    ，重定向编码302

• 请求转发的 / 表示：http://服务器ip:端口/项目名  ，请求转发编码307

 

下载文件代码：

public class FileServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1.获取要下载的文件路径
        String realPath = "F:\java_code\ServletCode\Servlet-response\src\main\resources\1.jpg";
        System.out.println("下载文件的路径：" + realPath);

        //2.获取下载文件名
        String fileName = realPath.substring(realPath.lastIndexOf("\") + 1);

        //3.设置浏览器支持，设置将文件名进行编码，防止中文乱码
        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);

        //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);
    }
}

验证码功能：

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

        //设置浏览器3秒刷新一次
        resp.setHeader("refresh","3");

        //在内存中建立一个图片
        BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);

        //得到图片
        Graphics2D g = (Graphics2D) image.getGraphics();

        //设置图片样式
        g.setColor(Color.gray);
        g.fillRect(0,0,80,20);

        //给图片填充数据
        g.setColor(Color.orange);
        g.setFont(new Font(null,Font.BOLD,20));
        g.drawString(makeNum(7),0,20);

        //设置浏览器打开图片的方式
        resp.setContentType("image/jpeg");
        //设置浏览器不缓存
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Pragma","no-cache");

        //将图片写给浏览器
        ImageIO.write(image,"jpg",resp.getOutputStream());

    }

    //生成随机数
    private String makeNum(int len) {
        Random random = new Random();
        StringBuffer num = new StringBuffer();
        while (len > 0) {
            num.append(random.nextInt(9) + "");
            len--;
        }
        return num.toString();
    }

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

重定向实现

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

        /*
        传入参数为项目打包的路径名（sr1）+重定向的路径名（image）
        resp.sendRedirect("/sr1/image");
        等价于下面语句
        resp.setHeader("Location","/sr1/image");
        resp.setStatus(302);
        */


        resp.sendRedirect("/sr1/image");
    }

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

重定向案例：登陆后重定向

1. 在index.jsp中登陆
2. 在RequestTestServlet中处理，然后重定向
3. 重定向到Success.jsp中

RequestTestServlet：

public class RequestTestServlet extends HttpServlet {

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

        String username = req.getParameter("username");
        String password = req.getParameter("password");

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

        resp.sendRedirect("/sr1/success.jsp");
    }

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

index.jsp：

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<body>
<h2>Hello World!</h2>

<%--${pageContext.request.contextPath}代表当前的项目名，login为web.xml中注册绑定的处理Servlet--%>
<form action="${pageContext.request.contextPath}/login" method="get">
    用户名：<input type="text" name="username"> <br>
    密码：<input type="password" name="password"> <br>
    <input type="submit">
</form>


</body>
</html>

success.jsp：

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>

<h1>Success</h1>

</body>
</html>

二.HttpServletRequest

HttpServletRequest代表客户端的请求，用户通过Http协议访问服务器，HTTP请求中的所有信息会被封装到HttpServletRequest，通过HttpServletRequest的方法，获得客户端的所有信息

1.HttpServletRequest中的一些方法：

2.主要应用

1. 获取前端传递的参数（主要是两个方法）

   1.  public String getParameter(String name); 

   2.  public String[] getParameterValues(String name); 

2. 请求转发

请求转发案例：前端提交登录表单，Servlet处理并转发

LoginServlet：

public class LoginServlet extends HttpServlet {

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

        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");

        String username = req.getParameter("username");

        String password = req.getParameter("password");

        String[] hobbys = req.getParameterValues("hobbys");

        System.out.println(username);
        System.out.println(password);
        System.out.println(Arrays.toString(hobbys));


        //通过请求转发
        req.getRequestDispatcher("/success.jsp").forward(req, resp);

    }

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

登录页面：index.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>登录</title>
</head>
<body>


<h1>登录</h1>
<div>
    <form action="${pageContext.request.contextPath}/login" method="post">
        用户名：<input type="text" name="username"> <br>
        密码：<input type="password" name="password"> <br>
        爱好：
        <input type="checkbox" name="hobbys" value="打篮球"> 打篮球
        <input type="checkbox" name="hobbys" value="写代码"> 写代码
        <input type="checkbox" name="hobbys" value="玩游戏"> 玩游戏
        <input type="checkbox" name="hobbys" value="看电影"> 看电影
        <br>

        <input type="submit">
    </form>
</div>

</body>
</html>

成功登录页面：success.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Success</title>
</head>
<body>

<h1>登录成功</h1>
</body>
</html>