java_文件流_以及文件上传下载

作者：@kuaiquxie
作者的github：https://github.com/bitebita
本文为作者原创，如需转载，请注明出处：https://www.cnblogs.com/dzwj/p/16124092.html

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import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;

public class FileToUnicode {
    public static void main(String args[]){
        try{
            FileInputStream fis = new FileInputStream("file1.txt");
            InputStreamReader dis = new InputStreamReader(fis);
            BufferedReader reader = new BufferedReader(dis);
            String s;
            while ((s = reader.readLine())!= null){
                System.out.println("read:"+s);
            }
            dis.close();
        }catch(IOException e){
            System.out.println(e);
        }

    }//main()
}//class

 

 

import java.io.IOException;
import java.io.PipedInputStream;
import java.io.PipedOutputStream;

public class PipedStreamDemo {
    public static void main(String args[])throws IOException
    {
        //建立管道连接
        PipedOutputStream pos = new PipedOutputStream();
        PipedInputStream pis = new PipedInputStream(pos);
        //数据赋值
        byte datamover = 0;
        System.out.println("start work...");
        try{
            System.out.println("transfer "+ datamover +" to pos.\n");
            //写入数据
            pos.write(datamover);
            //读取数据
            System.out.println("pis get "+(byte)pis.read());
        }finally{
            pis.close();
            pos.close();
        }
    }
}

 

 

import java.io.File;

public class UseFile {
    public static void main(String args[]){
        File f  = new File("file1.txt");
        System.out.println("the file is exists?   "+ f.exists());
        System.out.println("the file is write?   " + f.canWrite());
        System.out.println("the file is read ?   "+ f.canRead());
        System.out.println("the file is a file " +f.isFile());
        System.out.println("the file's path is ?    "+ f.getPath());
        System.out.println("the file's absolute path is "+ f.getAbsolutePath());
        System.out.println("the file's parent path is ?" + f.getParent());

        File newfile = new File("newfile.txt");

        f.renameTo(newfile);
        System.out.println(newfile.getName());
        System.out.println("if file is exists?" + f.exists());
        f.delete();
        newfile.delete();
        System.out.println("if file is exists?" + f.exists());

    }

}

 

 

 

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class CharInput {
    public static void main(String args[]) throws IOException {
        String s;
        InputStreamReader ir = new InputStreamReader(System.in);
        BufferedReader in = new BufferedReader(ir);
            while ((s = in.readLine())!= null){
            System.out.println("Read:"+ s );
        }
    }

}

 

 

import java.io.*;

public class FileInputStreamTest {

    public static void main(String[] args) {
        try{
            FileInputStream in = new FileInputStream("myfile.dat");
            while(in.available()>0){
                System.out.println(in.read()+ " ");
            }
            in.close();
        }catch(FileNotFoundException e){
            System.out.println("Error:Cannot open file for reading ");
        }catch(EOFException e){
            System.out.println("Error:EOF");
        }catch(IOException e ){
            System.out.println("Error:Cannot read from file ");
        }
    }
}

 

 

import java.io.*;
public class FileOutputStreamTest{
    public static void main (String args[]){
        try{
            FileOutputStream out = new FileOutputStream("myFile.dat");
            out.write('H');
            out.close();
        }catch(FileNotFoundException e)  {
            System.out.println("Error:Cannot open file for writing.");
        }catch(IOException e){
            System.out.println("Error:Cannot write to file.");
        }

    }
}

 

 

 

 

package com.xxxx.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet("/s01")
public class Servlet01 extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

//        通过session获取
        ServletContext  servletContext1 = request.getServletContext();

//        通过request获取
        ServletContext servletContext2 = request.getSession().getServletContext();
//        通过ServletConfig获取

        ServletContext servletContext3 = getServletConfig().getServletContext();

//        直接获取
        ServletContext servletContext4 = getServletContext();

//       获取根路径
        String realPath = request.getServletContext().getRealPath("/");
        System.out.println("真实路径："+realPath);
    }
}

 

 

package com.xxxx.wenjian;

import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.Part;
import java.io.IOException;


@WebServlet("/uploadServlet")
@MultipartConfig
public class UploadServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("文件上传");
//        设置请求的编码格式
        request.setCharacterEncoding("UtF-8");

        String uname = request.getParameter("uname");
        System.out.println("uname"+ uname);
//        获取Part对象（Servlet将Post请求封装成part对象
        Part part = request.getPart("myfile");
//        通过part对象得到上传的文件名
        String fileName = part.getSubmittedFileName();
        System.out.println("上传文件名："+ fileName);
//        得到文件的存放路径
        String filePath = request.getServletContext().getRealPath("/");
        System.out.println("文件存放的路径："+ filePath);
//        上传文件到指定目录
        part.write(filePath+"/"+ fileName);


    }
}

 

 

package com.xxxx.wenjian;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;

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

        System.out.println("下载文件");
//        编码一致
        response.setContentType("text/html; charset=UTF-8");
        request.setCharacterEncoding("UTF-8");
//         得到要下载的文件名
        String fileName = request.getParameter("fileName");
//        非空判断
        if(fileName == null ||"".equals(fileName.trim())){
            response.getWriter().write("请输入下载的文件名");
            response.getWriter().close();
            return;
        }
//        得到存放路径
        String path = request.getServletContext().getRealPath("/download/");
//        通过路径得到file对象
        File file = new File(path + fileName);
//        判断文件是否存在
        if(file.exists() && file.isFile()){
//            设置响应类型
        response.setContentType("text/html; charset=UTF-8");
//            设置响应头
            response.setHeader("Content-Disposition","attchment;fileName"+ fileName);

//            得到输入流
            InputStream in = new FileInputStream(file);
//            得到字节输出流
            ServletOutputStream out = response.getOutputStream();
            byte[] bytes = new byte[1024];
            int len = 0;
            while((len  = in.read(bytes)) != -1)
            {
                out.write(bytes,0,len);
            }
            out.close();
            in.close();
        }else{
            response.getWriter().write("文件名不存在，请重试");
            response.getWriter().close();
        }
    }
}

 

 

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>文件下载</title>
</head>
<body>

<a href="download/text.txt">文本</a>
<a href="download/text.rar">压缩</a>
<hr>
<a href="download/text.txt" download>文本</a>

<form action="downloadServlet">
    文件名：<input type="text" name="fileName" placeholder="请输入下载文件名">
    <button>下载</button>
</form>
</body>
</html>

 

 

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>文件上传</title>
</head>
<body>
<form method="post" enctype="multipart/form-data" action="uploadServlet">
    姓名：<input name="uname" type="text"> <br>
    文件：<input name="myfile" type="file"> <br>
    <button>提交</button>

</form>
</body>
</html>