Response of java learning

• Java

Response of java learning

0x00 Preface

Continuing from the previous article, this chapter updates the response.

0x01 Response

Common methods:

setStatus(int sc)  : 设置响应状态码

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

resp.sendRedirect(String Redirect);      302跳转

Forwarding and redirection are different here. Let's see the difference between them.

重定向：

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
			
转发：

1. 转发地址栏路径不变
2. 转发只能访问当前服务器下的资源
3. 转发是一次请求，可以使用request对象来共享数据

Redirect Code:

Response class:


@WebServlet("/response")
public class Response extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException {
        resp.setStatus(302);
        resp.setHeader("location","/demo1");
    }

    @Override
    protected void doPost(HttpServletRequest req,IOException {
        super.doPost(req,resp);
    }
}

Servletdemo class:


@WebServlet("/demo1")
public class ServeletDemo1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req,IOException {
        System.out.println("已跳转");
        resp.sendRedirect("http://www.baidu.com");
    }

    @Override
    protected void doPost(HttpServletRequest req,resp);
    }
}

The writer method uses:

@WebServlet("/response")
public class Response extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req,IOException {
        resp.setCharacterEncoding("gbk");   //设置编码
        PrintWriter writer = resp.getWriter();  //获取输出对象
        writer.write("response");//输出内容
        writer.println("1235");

    }

    @Override
    protected void doPost(HttpServletRequest req,resp);
    }
}

Output byte stream

ServletOutputStream outputStream = resp.getOutputStream();
        outputStream.write("abc".getBytes());

0x02 ServletContext

Common methods:


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

String getMimeType(String file)  : 获取MIME对象


域对象：共享数据

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

获取文件的真实(服务器)路径：

String getRealPath(String path)

File download case:

Write an HTML page with a hyperlink to download the pictures.

HTML：

<!DOCTYPE html>
<html lang="en">
<head>
    <Meta charset="UTF-8">
    <title>downlaod</title>
</head>
<body>

<a href="/demo/img/1.jpg">图片查看</a>

<a href="downloadServlet?filename=1.jpg">图片下载</a>

</body>
</html>

Downloadserlet class:

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


        this.doGet(request,response);
    }

    protected void doGet(HttpServletRequest request,IOException {


        String filename = request.getParameter("filename");  //接收filename传参的值
            ServletContext servletContext = this.getServletContext();   //创建servletContext 对象
            String Path = servletContext.getRealPath("/img/" + filename);  //获取文件真实路径

        String mimeType = servletContext.getMimeType(filename);//获取mimel类型





        FileInputStream fis = new FileInputStream(Path);   //路径参数文件输入流对象中
        response.setHeader("content-type",mimeType);  //响应头设置mime类型
        response.setHeader("content-disposition","attachment;filename="+filename); //设置为附件类型
            ServletOutputStream outputStream = response.getOutputStream();   //获取文件输出流
            byte[] buff = new byte[1024];   //设置每次读取的字节大小
            int len =0;
            while ((len = fis.read(buff))!=-1){     

                outputStream.write(buff,len);  
            }

    }
}

Here a simple case is completed.

0x03 end

The contents here are nothing more than the use of several methods, which reflects the power of java object-oriented language.

The content of this article comes from the network collection of netizens. It is used as a learning reference. The copyright belongs to the original author.
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