JavaWeb入门:HttpResponse和HttpRequest详解

• httpresponse 讲解
• httpservletresponse概述:
• response运行流程
• httprequest 讲解
• httpservletrequest概述
• request 运行流程
• servletcontext 作用域：

httpresponse 讲解

httpservletresponse概述:

​ 在创建servlet时会覆盖service()方法，或doget()/dopost(),这些方法都有两个参数，一个为代表请求的request和代表响应response。service方法中的response的类型是servletresponse，而doget/dopost方法的response的类型是httpservletresponse，httpservletresponse是servletresponse的子接口，功能和方法更加强大。

response运行流程

响应头有很多这里只介绍常用的。

在浏览器可以按f12 抓包看响应头、请求头、具体的可以再查。

设置响应行

设置响应的状态码

/**
 * @author: crush
 * @date: 2021-05-09 19:35
 * version 1.0
 */
@webservlet("/test3")
public class httpresponsetest3 extends httpservlet {
    @override
    protected void doget(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        system.out.println("设置状态码,前台通过判断状态码，来判断请求是否成功");
        resp.setstatus(404);
    }
    @override
    protected void dopost(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        doget(req, resp);
    }
}

测试

设置响应头

刷新 跳转页面

/**
 * @author: crush
 * @date: 2021-05-09 19:35
 * version 1.0
 */
@webservlet("/test4")
public class httpresponsetest4 extends httpservlet {
    @override
    protected void doget(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        // 设置响应头 每1秒自动刷新
        system.out.println("设置响应头 每1秒自动刷新");
        resp.setheader("refresh", "1");
        //定时跳转 3秒后将自动跳转
//        resp.setheader("refresh","3;url=hello.jsp");
    }
    @override
    protected void dopost(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        doget(req, resp);
    }
}

测试

一个小demo 实现刷新 页面累加

/**
 * response
 * @author adimi
 */
@webservlet("/test4")
public class responsetest4 extends httpservlet {
    private static integer id=1;
    @override
    protected void doget(httpservletrequest request, httpservletresponse response) throws servletexception, ioexception {
        response.setheader("refresh","1");
        printwriter writer = response.getwriter();
        id++;
        writer.print("id==>"+id);
    }
    @override
    protected void dopost(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        doget(req, resp);
    }
}

设置字符编码 解决中文乱码问题

/**
 * @author: crush
 * @date: 2021-05-09 19:35
 * version 1.0
 */
@webservlet("/test1")
public class httpresponsetest1 extends httpservlet {
    @override
    protected void doget(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        // 解决中文乱码问题
        // 设置响应头
        // 设置字符编码 resp.setcharacterencoding("utf-8");
        // 设置响应内容以什么格式展示到页面 什么编码格式 包含了设置字符编码
        resp.setcontenttype("text/html;charset=utf-8");
        printwriter writer = resp.getwriter();
        writer.print("中国,你好！！！");
    }
    @override
    protected void dopost(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        doget(req, resp);
    }
}

测试

重定向 redirect

/**
 * 重定向
 * @author: crush
 * @date: 2021-05-09 19:35
 * version 1.0
 */
@webservlet("/test5")
public class httpresponsetest5 extends httpservlet {
    @override
    protected void doget(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        resp.sendredirect("hello.jsp");
//        resp.setheader("location","www.baidu.com"); 通过设置响应头转发
    }
    @override
    protected void dopost(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        doget(req, resp);
    }
}

request转发

/**
 * 重定向
 * @author: crush
 * @date: 2021-05-09 19:35
 * version 1.0
 */
@webservlet("/test5")
public class httpresponsetest5 extends httpservlet {
    @override
    protected void doget(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
//        resp.sendredirect("hello.jsp");
        req.getrequestdispatcher("hello.jsp").forward(req,resp);
    }
    @override
    protected void dopost(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        doget(req, resp);
    }
}

重定向和转发的区别

文件下载

获取路径资源

string path=this.getservletcontext().getrealpath("web-inf\\classes\\8.jpg");

读取资源

fileinputstream fileinputstream=new fileinputstream(path);

获取到文件名，路径在电脑上保存的形式是 \ \

string filename=path.substring(path.lastindexof("\\")+1);

设置消息头告诉浏览器，我要下载1.png这个图片 设置编码

resp.setheader("content-disposition", "attachment; filename=" + urlencoder.encode(filename, "utf-8"));

把读取到的内容回送给浏览器

 int len=0;
byte[] bytes=new byte[1024];
// servletoutputstream 提供用于将二进制数据发送到客户端的输出流
servletoutputstream servletoutputstream=resp.getoutputstream();
while((len=fileinputstream.read(bytes))>0) {
    servletoutputstream.write(bytes,0,len);
}

关闭资源

servletoutputstream.close();
        fileinputstream.close();

注：8.jpg 放在我的resources 文件夹下 但是这里需要写的是编译完8.jpg存放的位置

具体代码

/**
 * @author: crush
 * @date: 2021-05-09 19:40
 * version 1.0
 */
@webservlet("/down")
public class responsedownfile extends httpservlet {
    @override
    protected void doget(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        //获取路径资源
        string path=this.getservletcontext().getrealpath("web-inf\\classes\\8.jpg");
        //读取资源
        fileinputstream fileinputstream=new fileinputstream(path);
        //获取到文件名，路径在电脑上保存的形式是\\
        string filename=path.substring(path.lastindexof("\\")+1);
        //设置消息头告诉浏览器，我要下载1.png这个图片
        // 该方式文件名为中文时会乱码
        //防止中文乱码
        resp.setheader("content-disposition", "attachment; filename=" + urlencoder.encode(filename, "utf-8"));
        //把读取到的内容回送给浏览器
        int len=0;
        byte[] bytes=new byte[1024];
        servletoutputstream servletoutputstream=resp.getoutputstream();
        while((len=fileinputstream.read(bytes))>0) {
            servletoutputstream.write(bytes,0,len);
        }
        // 关闭资源
        servletoutputstream.close();
        fileinputstream.close();
    }
    @override
    protected void dopost(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        doget(req, resp);
    }
}

httprequest 讲解

httpservletrequest概述

​ 我们在创建servlet时会覆盖service()方法，或doget()/dopost(),这些方法都有两个参数，一个为代表请求的request和代表响应response。service（）方法中写了根据请求方式的不同调用doget()和dopost().

service方法中的request的类型是servletrequest，而doget/dopost方法的request类型httpservletrequest，httpservletrequest是servletrequest的子接口，功能和方法更加强大.

request 运行流程

获取请求携带的参数

/**
 * @author: crush
 * @date: 2021-05-11 16:52
 * version 1.0
 */
@webservlet("/request1")
public class requesttest1 extends httpservlet {
    @override
    protected void doget(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        // 这里是请求的参数名  必须是同名的 
        string username = req.getparameter("username"); 
        string password = req.getparameter("password");
        printwriter writer = resp.getwriter();
        writer.print("<h1>"+username+":"+password+"</h1>");
    }
    @override
    protected void dopost(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        doget(req, resp);
    }
}

获取多个参数的值

  @override
    protected void doget(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        // 设置请求的编码  不然会乱码
        req.setcharacterencoding("utf-8");
        enumeration<string>  names = req.getparameternames();
        while (names.hasmoreelements()) {
            string name = (string) names.nextelement();
            string[]  values = req.getparametervalues(name);
            system.out.println(name+":"+ arrays.tostring(values));
        }
    }

获得请求行的信息

/**
 * @author: crush
 * @date: 2021-05-11 16:52
 * version 1.0
 */
@webservlet("/request3")
public class requesttest3 extends httpservlet {
    @override
    protected void doget(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        // 获得请求的url
        stringbuffer requesturl = req.getrequesturl();
        system.out.println("请求的url===>"+requesturl);
        // 获得请求的servlet的路径
        string path = req.getservletpath();
        system.out.println("请求的servlet的路径===>"+path);
        //返回发出此请求的http方法的名称，例如get，post或put
        string method = req.getmethod();
        system.out.println("返回发出此请求的http方法的名称==>"+method);
        //返回发送请求的客户端或最后一个代理的internet协议（ip）地址
        string remoteaddr = req.getremoteaddr();
        system.out.println("remoteaddr==>"+remoteaddr);
    }
    @override
    protected void dopost(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        doget(req, resp);
    }
}

request实现转发

/**
 * @author: crush
 * @date: 2021-05-11 16:52
 * version 1.0
 */
@webservlet("/request2")
public class requesttest2 extends httpservlet {
    @override
    protected void doget(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        // 访问request2 转发到 request4去
        req.getrequestdispatcher("/request4").forward(req,resp);
    }
    @override
    protected void dopost(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        doget(req, resp);
    }
}

request是一个域对象

request对象也是一个存储数据的区域对象，所以也具有如下方法：

setattribute(string name, object o)

getattribute(string name)

removeattribute(string name)

servletcontext 作用域：

创建：启动web应用程序的时候创建

销毁：关闭web应用程序的时候销毁

域的作用范围：整个web应用的启动周期

request作用域：

创建：访问时创建request

销毁：响应结束request销毁

域的作用范围：一次请求中

总结

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