Servlet请求和响应

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原创最新推荐文章于 2026-03-15 00:18:23 发布 338 阅读 AI 写同款· GEO 优化 ›

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Servlet请求

Servlet请求对应的是ServletRequest对象，它有一个子类HttpServletRequet基于Http协议的规则对请求数据进行了封装。我们可以使用HttpServletRequet对象的方法来获取请求数据，来完成功能的开发。

1.获取路径的方法

public String getContextPath()
    获取虚拟目录路径
public String getServletPath()
    获取Servlet的映射路径
public String getRemoteAddr()
    获取访问者的ip地址
public String getQueryString()
    获取请求的消息数据
public String getRequestURI()
    获取统一资源标识符
public String getRequestURL()
    获取统一资源定位符

@WebServlet("/servletRequestDemo1")
public class ServletRequestDemo1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取虚拟目录
        String contextPath = req.getContextPath();
        System.out.println("虚拟目录："+contextPath); 

        //获取Servlet映射路径
        String servletPath = req.getServletPath();
        System.out.println("servlet访问路径："+servletPath);

        //获取访问者ip地址: 
        String remoteAddr = req.getRemoteAddr();
        System.out.println("访问者ip："+remoteAddr);

        //获取统一资源标识符
        String requestURI = req.getRequestURI();
        System.out.println("资源标识符："+requestURI);

        //获取统一资源定位符
        StringBuffer requestURL = req.getRequestURL();
        System.out.println("统一资源定位符："+requestURL);
    }

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

2.获取请求头信息

请求头是浏览器告诉服务器的一些请求配置信息，以键值对的形式存在。

public String getHeader(String name)
    获取一个请求头的值
public Enumeration<String> getHeaders(String name)
    获取一个请求头的多个值
public Enumeration<String> getHeadNames()
    获取所有请求头名称

@WebServlet("/servletRequestDemo2")
public class ServletRequestDemo2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取一个请求头
        String connection = req.getHeader("connection");
        System.out.println(connection);
        System.out.println("----------------");

        //获取一个请求头的多个值
        Enumeration<String> values = req.getHeaders("accept-encoding");
        while (values.hasMoreElements()) {
            String value = values.nextElement();
            System.out.println(value);
        }

        System.out.println("------------");

        //获取所有的请求头名称
        Enumeration<String> headerNames = req.getHeaderNames();
        //遍历请求头名称，根据名称获取值
        while (headerNames.hasMoreElements()) {
            String headName = headerNames.nextElement();
            String headValue = req.getHeader(headName);
            System.out.println(headName+"="+headValue);
        }
    }

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

3.获取请求参数信息

public String getParameter(String name)
    根据参数名获取一个参数值
public String[] getParameterValues(String name)
    根据参数名获取多个参数值
public Enumeration<String> getParameterNames()
    获取所有的参数名称
public Map<String,String[]> getParameterMap()
    获取所有的参数名和参数值，并封装为Map集合

创建一个regist.html页面（参考源代码），然后使用Servlet获取参数信息

@WebServlet("/servletRequestDemo3")
public class ServletRequestDemo3 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //根据参数名获取参数指
        String username = req.getParameter("username");
        System.out.println("姓名："+username);

        //根据参数名获取多个值
        String[] hobbies = req.getParameterValues("hobby");
        System.out.println("爱好："+ Arrays.toString(hobbies));
        System.out.println("---------");
        
        //获取所有的参数名称
        Enumeration<String> parameterNames = req.getParameterNames();
        while (parameterNames.hasMoreElements()) {
            String parameterName = parameterNames.nextElement();
            String[] values = req.getParameterValues(parameterName);
            System.out.println(parameterName+":"+Arrays.toString(values));
        }
        System.out.println("----------");

        //获取所有的参数名和参数指，存入一个Map集合
        Map<String, String[]> parameterMap = req.getParameterMap();
        Set<String> keys = parameterMap.keySet();
        for (String key : keys) {
            String[] values = parameterMap.get(key);
            System.out.println(key+"="+Arrays.toString(values));
        }
    }

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

4.请求数据封装对象

需要用到beanutils工具类，把jar包复制到web/WEB-INF/libs目录下

@WebServlet("/servletRequestDemo5")
public class ServletRequestDemo5 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取所有的参数名和参数指，存入一个Map集合
        Map<String, String[]> parameterMap = req.getParameterMap();
        Student stu=new Student();
        try {
            BeanUtils.populate(stu,parameterMap);
            System.out.println(stu);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

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

5.请求数据乱码解决

//设置请求字符编码
req.setCharacterEncoding("utf-8");

6.请求转发-请求域

当客户端请求一个Servlet1时，Servlet1可以将请求转发给Servlet2，同时可以转发过程中共享数据。多次转发形成的一条请求链，叫做请求域。可以在请求域访问内共享数据。

在Servlet7中设置共享数据

@WebServlet("/servletRequestDemo7")
public class ServletRequestDemo7 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //设置请求编码
        req.setCharacterEncoding("utf-8");

        //设置请求参数
        req.setAttribute("user","李四");
        req.getRequestDispatcher("/servletRequestDemo8").forward(req,resp);
    }

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

在Servlet8中获取共享数据

@WebServlet("/servletRequestDemo8")
public class ServletRequestDemo8 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //设置请求编码
        req.setCharacterEncoding("utf-8");

        //获取请求共享数据
        Object user = req.getAttribute("user");
        System.out.println(user);
    }

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

Servlet响应

浏览器访问服务器后，服务器给客户端响应的数据会封装为ServletResponse对象，它有一个子类叫HttpServletResponse对象，用于封装按照Http协议封装的响应数据。

1.响应状态码

状态码	状态
100	只有请求的一部分已经被服务器接收，但只要它没有被拒绝，客户端应继续该请求
200	请求成功
302	重定向，所请求的页面已经临时转移到一个新的 URL
304	访问缓存，所请求的页面已经临时转移到一个新的 URL
404	客户端错误，请求路径服务器没有对应的资源
405	客户端错误，请求方式找不到对应的方法
500	服务端错误，可能服务器内部有异常

2.响应数据乱码解决

//设置响应编码
resp.setContentType("text/html;charset=utf-8");

使用字符流响应数据

@WebServlet("/servletResponseDemo1")
public class ServletResponseDemo1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //设置响应编码
        resp.setContentType("text/html;charset=utf-8");
        //输出响应数据
        resp.getWriter().println("<h1>你好，这是一个响应消息</h1>");
    }

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

使用字节流响应数据

@WebServlet("/servletResponseDemo2")
public class ServletResponseDemo2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //设置响应编码
        resp.setContentType("text/html;charset=utf-8");
        //输出响应数据
        ServletOutputStream outputStream = resp.getOutputStream();
        outputStream.write("你好世界".getBytes("utf-8"));
    }

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

3.响应图片

在web/img目录下放一张a.jpeg图片，把图片中所有的字节响应给客户端。

@WebServlet("/servletResponseDemo3")
public class ServletResponseDemo3 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取输出流对象
        ServletOutputStream out = resp.getOutputStream();
        //获取文件的绝对路径
        String imgPath = getServletContext().getRealPath("img/a.jpeg");
        //获取输入流对象
        FileInputStream fis = new FileInputStream(imgPath);
        byte[] bs=new byte[1024];
        int len;
        while ((len=fis.read(bs))!=-1){
            out.write(bs,0,len);
        }
        fis.close();
    }

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

5.设置定时刷新

@WebServlet("/servletResponseDemo5")
public class ServletResponseDemo5 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setHeader("Refresh","3;url=/day03_Servlet/login.html");
        resp.setContentType("text/html;charset=utf-8");
        resp.getWriter().println("你好世界 三秒钟跳转到登录页面");
    }

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

6.重定向

重定向和请求转发不太一样，请求转发是只有一个请求，而重定向有两次请求。所以重定向不能通过请求域共享数据，只有在同一个请求链中才能通过请求域中心数据。

@WebServlet("/servletResponseDemo6")
public class ServletResponseDemo6 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html;charset=utf-8");
        //重定向到servletResponseDemo5
        //resp.sendRedirect(req.getContextPath()+"/servletResponseDemo5");

        //也可以使用下面两个方法，完成重定向；302表示重定向的状态码
        resp.setStatus(302);
        resp.setHeader("location",req.getContextPath()+"/servletResponseDemo5");
    }

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

7.文件下载

写一个html页面，点击图片开始下载

<a href="/day03_Servlet/servletResponseDemo7">点击下载图片</a>

写以Servlet处理下载的请求，给客户端响应一张图片

@WebServlet("/servletResponseDemo7")
public class ServletResponseDemo7 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //准备要下载的图片
        File file=new File("img/a.jpeg");

        //设置响应头，告诉浏览器以附件形式接受
        resp.setHeader("content-disposition","attachment;filename="+file.getName());

        //获取输出流对象
        ServletOutputStream out = resp.getOutputStream();
        //获取文件的绝对路径
        String imgPath = getServletContext().getRealPath(file.getPath());
        //获取输入流对象
        FileInputStream fis = new FileInputStream(imgPath);
        byte[] bs=new byte[1024];
        int len;
        while ((len=fis.read(bs))!=-1){
            out.write(bs,0,len);
        }
        fis.close();
    }

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