java响应gzip Java响应对象输出字符限制

admin2024-06-11  10

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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