java响应gzip Java响应对象输出字符限制

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mob6454cc7203e2 2024-06-10 20:44:13

文章标签 java响应gzip System java 服务器 文章分类 Java 后端开发

添加模板

package ${enclosing_package};

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ${primary_type_name} extends HttpServlet {

    public void doGet(HttpServletRequest request,
                      HttpServletResponse response)
                      throws ServletException, IOException {

            ${cursor}  
    }

设置全局配置信息

public class Demo01 extends HttpServlet {

//  public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//        //先获取config对象
//      ServletConfig servletConfig = this.getServletConfig();
//      //取出servlet的配置信息
//      String value = servletConfig.getInitParameter("username");
//      System.out.println(value);
//  }
//
//  public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//      doGet(request, response);
//  }
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       //获取context域对象
        ServletContext application = this.getServletContext();
        //获取全局配置信息
        String value = application.getInitParameter("key");
        System.out.println(value);
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

获取服务器真实文件上的路径并读取

使用Context域对象获取，可以获取到服务器上任意资源路径

public class Demo02 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 获取a文件
        ServletContext context1 = this.getServletContext();
        // 获取服务器上的真实路径(绝对路径 磁盘路径)
        String path1 = context1.getRealPath("/WEB-INF/classes/a.properties");
        System.out.println(path1);
        // 读取文件
        Properties properties1 = new Properties();
        properties1.load(new FileInputStream(path1));
        System.out.println(properties1.getProperty("key"));

        //读取b文件 /WEB-INF/classes/com/lanou/demo/b.properties
        ServletContext context2 = this.getServletContext();
        String path2 = context2.getRealPath("/WEB-INF/classes/com/lanou/demo/b.properties");
        System.out.println(path2);
        Properties properties2 = new Properties();
        properties2.load(new FileInputStream(path2));
        System.out.println(properties2.getProperty("key"));

        //读取c文件 /WEB-INF/c.properties
        ServletContext context3 = this.getServletContext();
        String path3 = context3.getRealPath("/WEB-INF/classes/com/lanou/demo/b.properties");
        System.out.println(path3);
        Properties properties3 = new Properties();
        properties3.load(new FileInputStream(path3));
        System.out.println(properties3.getProperty("key"));
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

请求转发

浏览器只是发起了一次请求
servlet内部做了请求转发浏览器并不知道

public class Demo03 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("Guess who I am?");
        System.out.println("I don't know，你让demo04猜猜");
        //获取context域对象
        ServletContext context = this.getServletContext();
        //从context域中 获取请求转发器
        RequestDispatcher dispatcher = context.getRequestDispatcher("/demo04");
        //进行请求转发
        dispatcher.forward(request, response);
        System.out.println("I do，哈哈");
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

public class Demo04 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        System.out.println("I tell you");
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

HttpServletResponse 服务器的响应对象

响应对象中都有什么？
1.响应行 http/1.1 状态码200
2.响应头告诉浏览器我要做什么例如响应给你的文件需要下载以什么编码格式解析数据
3.响应体响应回浏览器的数据

public class Demo05 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.设置编码格式服务器的编码格式，默认tomcat iso-8859-1
        //response.setCharacterEncoding("UTF-8");
        //告诉浏览器要使用什么编码格式来查看
        //2.添加响应头
        //response.setHeader("Content-type", "text/html;charset=UTF-8");
        //这句代表以上两句的方法
        response.setContentType("text/html;charset=UTF-8");
        //响应给浏览器一句话
        //从响应对象HttpServletResponse中获取流对象
        //注意：这个流对象不是你自己创建，要从响应中获取
        PrintWriter out = response.getWriter();
        out.write("啦啦啦啦");
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

下载文件

用户发送请求，请求到访问servlet
Servlet处理请求(把服务器上的图片，以流的形式，使用response响应给用户浏览器)

public class Demo06 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {


        // 获取服务器上的图片路径
        String path = this.getServletContext().getRealPath("/WEB-INF/classes/1.jpeg");
        //字符串切割，获取图片的名字
        int index = path.lastIndexOf("/");
        String filename = path.substring(index+1);
        System.out.println(filename);
        //修改文件名字的字符集
        filename = new String(filename.getBytes(), "iso-8859-1");
        //添加响应头(需要拼接文件的名字)
        response.setHeader("content-disposition", "attachment;filename="+filename);
        //告诉浏览器文件下载的格式添加响应头
        response.setHeader("content-type", "image/jpeg");
        // 从服务器中读取图片
        FileInputStream fis = new FileInputStream(path);
        //注意：需要获取response当中的字节流进行数据的响应
        ServletOutputStream sos = response.getOutputStream();
        // 边读边写
        int len = 0;
        byte[] b = new byte[1024];
        while((len = fis.read(b)) != -1) {
            //响应回浏览器
            //如果只是单纯的吧图片响应回去，浏览器并不知道你要干啥(下载或浏览)
            //需要通过响应头 通知浏览器 我给你这个文件，是下载用的
            sos.write(b,0,len);
        }
        //注意：自己创建的流自己关
        fis.close();
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

请求重定向

请求重定向和请求转发的区别
请求重定向是发起的两次请求(请求地址发生了变化)
响应时要注意细节
从response获取的字符流和字节流，在一个servlet中不能同时使用

public class Demo07 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //通过请求头的方式，请求重定向
        //System.out.println("我要借钱");
        //System.out.println("我没有，去找demo08");
        //添加重定向响应头
        //注意：添加头信息网址的时候，需要写明工程名
        //response.setHeader("location","/java-web-servlet-3.27/demo08");
        //添加重定向状态码
        //response.setStatus(302);
        //System.out.println("我去了");

        //添加刷新头(每秒刷新一次)
        //response.setIntHeader("refresh",1);
        //添加随机数
        //response.getWriter().write(Math.random() + "");

        //设置响应的字符集
        response.setContentType("text/html;charset=UTF-8");
        //三秒后跳转一个网址
        response.setHeader("refresh", "3;url=/java-web-servlet-3.27/demo08");
        response.getWriter().write("三秒后跳转");

    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

HttpServletRequest 用户的请求对象

包含了请求行，请求头，请求体

public class Demo08 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        System.out.println(request);
        //System.out.println("我借了");
        ///java-web-servlet-3.27/demo08
        System.out.println(request.getRequestURI());
        //http://localhost:8080/java-web-servlet-3.27/demo08
        System.out.println(request.getRequestURL());

        //获取请求的类型(用浏览器直接请求的都是Get请求)
        System.out.println(request.getMethod());
        //获取请求路径(相对路径)
        System.out.println(request.getContextPath());

        //获取请求中携带的参数
        //参数是你提交表单的时候，表单的name属性
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        System.out.println(username + " " + password);
        //判断浏览器
        //可以通过请求中的信息获取用户使用浏览器
        String header = request.getHeader("User-Agent");
        System.out.println(header);
        if(header.toLowerCase().contains("firefox")) {
            System.out.println("用的是火狐");
        }else if(header.toLowerCase().contains("chrome")){
            System.out.println("用的是谷歌");
        }else {
            System.out.println("其他浏览器");
        }
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

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