Request对象和response对象

一、概念

request对象和response对象是通过Servlet容器（如Tomcat）自动创建并传递给Servlet的。

Servlet容器负责接收客户端的请求，并将请求信息封装到request对象中，然后将request对象传

递给相应的Servlet进行处理。类似地，Servlet容器会创建一个response对象，并将其传递给

Servlet，用于生成响应并发送给客户端。

总的来说，request对象是来获取请求消息，response对象是来设置响应消息

二、Request

在Servlet的service()方法被调用时，Servlet容器会创建一个包含请求信息的HttpServletRequest对象，并将其作为参数传递给Servlet的service()方法。类似地，Servlet容器还会创建一个HttpServletResponse对象，并将其作为参数传递给Servlet的service()方法。

1、Request功能

（1）获取请求行数据

请求行的数据有：请求方式请求url 请求协议/协议版本号

①获取请求方式：getMethod()

②获取虚拟目录：getContextPath()

③获取servlet路径：getServletPath()

④获取get方式请求参数：getQueryString()

⑤获取请求URI：统一资源定位符：getRequestURI()

统一资源标识符：getRequestURL()

⑥获取协议及版本： getProtocol()

⑦获取客户机的IP地址：getRemoteAddr()

代码示例：

@WebServlet("/requestDemo1")
public class RequestDemo1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1获取请求方式
        String method=request.getMethod();
        System.out.println(method);
        //2获取虚拟目录
        String contextPath = request.getContextPath();
        System.out.println(contextPath);
        //3获取servlet路径
        String servletPath = request.getServletPath();
        System.out.println(servletPath);
        //4获取请求参数
        String queryString = request.getQueryString();
        System.out.println(queryString);
        //5获取请求URI
        String requestURI = request.getRequestURI();
        System.out.println(requestURI);
        StringBuffer requestURL = request.getRequestURL();
        System.out.println(requestURL);
        //6获取请求协议及版本号
        String protocol = request.getProtocol();
        System.out.println(protocol);
        //7获取客户机的ip地址
        String remoteAddr = request.getRemoteAddr();
        System.out.println(remoteAddr);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }
}

（2）获取请求头数据

方法：getHeader(String name):通过请求头的名称获取请求头的值

getHeaderNames():获取所有的请求头名称

@WebServlet("/requestDemo2")
public class RequestDemo2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //演示获取请求头数据
        //获取所以请求头数据
        Enumeration<String> headerNames = request.getHeaderNames();
        //遍历
        while(headerNames.hasMoreElements()){
            String s = headerNames.nextElement();
            //根据名称获取请求头的值
            String header = request.getHeader(s);
            System.out.println(s+"......"+header);
        }
        //演示获取请求头数据:user-Agent
        String header = request.getHeader("user-agent");
        //判断agent的浏览器版本
        System.out.println(header);
      
    }

（3）获取请求体数据

只有post请求有请求体

步骤：①获取流对象
BufferedReader getReader()：获取字符输入流，只能操作字符数据
ServletInputStream getInputStream()：获取字节输入流，可以操作所有类型数据

② 再从流对象中拿数据

@Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取请求消息体--请求参数
        //1、获取字符流
        BufferedReader reader = request.getReader();
        //2、读取数据
        String line=null;
        while((line=reader.readLine())!=null){
            System.out.println(line);
        }
        System.out.println("-------------------------------------");
    }

2、其他功能

（1）获取请求参数（不区分post和get方法）

①根据参数名称获取参数值：getParameter(String name)

②根据参数名称获取参数值数组：getParameterValues(String name)

③获取所有请求的参数名称：getParameterNames()

④获取所有参数的map集合：getParameterMap()

@WebServlet("/requestDemo4")
public class RequestDemo4 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
     this.doPost(request,response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //解决中文乱码问题
        request.setCharacterEncoding("utf-8");
        //根据请求参数的名称获取请求参数值
        String username = request.getParameter("username");
        System.out.println(username);
        System.out.println("post");
        System.out.println();
        //根据参数名称获取请求参数数组
        String[] parameterValues = request.getParameterValues("hobby");
        for (String hobby:parameterValues) {
            System.out.println(hobby);
        }
        System.out.println();

        //根据所以请求参数名称
        Enumeration<String> parameterNames = request.getParameterNames();
        while(parameterNames.hasMoreElements()){
            String s = parameterNames.nextElement();
            System.out.print(s);
            String parameter = request.getParameter(s);
            System.out.println(parameter);
        }
        System.out.println();

        //获取所以参数的map集合
        Map<String, String[]> parameterMap = request.getParameterMap();
        Set<String> strings = parameterMap.keySet();
        for(String name:strings){
            String[] strings1 = parameterMap.get(name);
            System.out.print(name);
            for(String value:strings1){
                System.out.println(value);
            }
        }
    }
}

（2）请求转发

在服务器内部的资源跳转方式

步骤：

通过request对象获取请求转发器对象：getRequestDispatcher(String path)。

使用RequestDispatcher对象来进行转发：forward(ServletRequest request, ServletResponse response) 。

特点：

浏览器地址栏不发生改变

只能转发到当前服务器内部资源中

转发是一次请求

（3）共享数据

域对象：一个有作用范围的对象，可以在范围内共享数据
request域：代表一次请求的范围，一般用于请求转发的多个资源中共享数据
方法：
①setAttribute(String name,Object obj):存储数据
②getAttitude(String name):通过键获取值
③ void removeAttribute(String name):通过键移除键值对
注意：这个放于forward方法的上面，不然响应太快会导致无法获取信息！

代码示例：

@WebServlet("/requestDemo5")
public class RequestDemo5 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("demo5被访问了");
        request.setAttribute("ttt","hhhh");
        //转发到demo6
        request.getRequestDispatcher("/requestDemo6").forward(request,response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }
}


@WebServlet("/requestDemo6")
public class RequestDemo6 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        Object ttt = request.getAttribute("ttt");
        System.out.println(ttt);
        System.out.println("demo6被访问了");
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }
}

（4）获取ServletContext对象：getServletContext()

三、Response

response：设置响应消息

1、设置响应行方法

（1）设置响应行状态码方法：setStatus（）；

（2）设置响应头：setHeader（String name，String value）

（3）设置响应体：

使用步骤：

①获取输出流
字符输出流：PrintWriter getWriter()

字节输出流：ServletOutputStream getOutputStream()

② 使用输出流，将数据输出到客户端浏览器

2、重定向：一种资源跳转的方式

（1）方法：sendRedirect(）

（2）重定向的特点:redirect
           ① 地址栏发生变化
           ② 重定向可以访问其他站点(服务器)的资源
           ③ 重定向是两次请求。不能使用request对象来共享数据

@WebServlet( "/responseDemo1")
public class responseDemo1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("demo1");
        //设置状态码为302
        response.setStatus(302);
       /* //设置响应头location
        response.setHeader("location","/servlet/responseDemo2");*/
        //获取当前应用程序的上下文路径
        String contextPath = request.getContextPath();

        //简单的重定向方法
        response.sendRedirect(contextPath+"/responseDemo2");
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request,response);
    }
}

@WebServlet("/responseDemo2")
public class responseDemo2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("demo2");
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request,response);
    }
}

（3）服务器输出字符数据到浏览器

步骤：
获取字符输出流
输出数据

@WebServlet("/responseDemo3")
public class responseDemo3 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        /*//获取流对象之前，设置流的默认编码：ISO-8859-1设置为：浏览器默认编码
        response.setCharacterEncoding("utf-8");
        //告诉浏览器服务器发送的消息体数据的编码，建议浏览器使用改编码解码
        response.setHeader("content-type","text/html;charset=utf-8");*/
        response.setContentType("text/html;charset=utf-8");//解决乱码问题
        //获取字符输出流
        PrintWriter writer = response.getWriter();
        //输出数据
        writer.write("牛牛牛");
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request,response);
    }
}

（4）服务器输出字节数据到浏览器
步骤：
获取字节输出流
输出数据

@WebServlet("/responseDemo4")
public class responseDemo4 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        //获取字节输出流
        ServletOutputStream outputStream = response.getOutputStream();
        //输出数据
        outputStream.write("你好".getBytes());
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request,response);
    }
}

三、ServletContext对象

1、概念

ServletContext 实例代表了整个 Web 应用程序的上下文环境，可以在整个应用程序中访问和共享，可以和服务器来通信。

2、获取

方式一：

通过request对象获取：request.getServletContext();

方式二：

通过HttpServlet获取：this.getServletContext();

3、功能

（1）获取MIME类

MIME类型:在互联网通信过程中定义的一种文件数据类型
格式：大类型/小类型 text/html image/jpeg

获取方法：getMimeType(String file)

代码示例：

@WebServlet("/ContextDemo1")
public class ContextDemo1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取Context对象的方式
       // ServletContext servletContext = request.getServletContext();
        ServletContext servletContext1 = this.getServletContext();
        //定义文件名称
        String filename="a.jpg";
        //获取MIME类型
        String mimeType = servletContext1.getMimeType(filename);
        System.out.println(mimeType  );
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request,response);
    }
}

（2）域对象：共享数据

① setAttribute(String name,Object value)
② getAttribute(String name)
③removeAttribute(String name)

ServletContext对象范围：所有用户所有请求的数据


@WebServlet(name = "ContextDemo2", value = "/ContextDemo2")
public class ContextDemo2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext servletContext1 = this.getServletContext();
        servletContext1.setAttribute("n","hello");
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request,response);
    }
}


@WebServlet(name = "ContextDemo2", value = "/ContextDemo2")
public class ContextDemo3 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext servletContext1 = this.getServletContext();
        Object n = servletContext1.getAttribute("n");
        System.out.println(n);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request,response);
    }
}