使用Servlet處理一個上傳的文件

2024-07-14 08:43:26

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Servlet中可以使用post請求上傳文件，使用getReader()和getInputStream()自己處理，也可以使用getPart()或getParts()封裝了一些功能的方法處理，getParts()可以同時上傳多個文件。接下來使用四個Demo來練習一下使用方法

一.使用getReader()和getInputStream()

Demo1

<!-- 這是HTML代碼塊，窗體網頁上顯示的是一個選擇文件的input框和一個upload的button --><!DOCTYPE html><html> <head>  <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">  <title></title> </head> <body>  <form action="upload" method="post" enctype="multipart/form-data">  選擇文件：<input type="file" name="filename" value="" /><br>  <input type="submit" value="Upload" name="upload" />  </form> </body></html>

//這是Servlet處理部分import java.io.DataInputStream;import java.io.FileOutputStream;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;//Servlet implementation class uploadServlet@WebServlet("/upload")public class UploadServlet extends HttpServlet { private static final long serialVersionUID = 1L; //@see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) protected void doPost(HttpServletRequest request, HttpServletResponse response)   throws ServletException, IOException {  //讀取請求Body  byte[] body = readBody(request);  //取得所有Body內容的字符串表示  String textBody = new String(body, "ISO-8859-1");  //取得上傳的文件的文件名(取得路徑并分離)  String filename = getFilename(textBody);  //取得文件內容在Body中的首尾索引  Position p = getFilePosition(request, textBody);  //將內容輸出到文件  writeTo(filename, body, p); } //存放索引的類 class Position{  int begin;  int end;  Position(int begin, int end) {   this.begin = begin;   this.end = end;  } } //讀取請求body private byte[] readBody(HttpServletRequest request) throws IOException {  int formDataLength = request.getContentLength();  //獲得ServletInputStream對象  //getReader()和getInputStream()只能則一調用，否則會拋出IllegalStateException異常  DataInputStream dataStream = new DataInputStream(request.getInputStream());  byte[] body = new byte[formDataLength];  int totalBytes = 0;  while(totalBytes < formDataLength) {   int bytes = dataStream.read(body, totalBytes, formDataLength);   totalBytes += bytes;  }  return body; } //取得上傳文件名稱 private String getFilename(String reqBody) {  //獲取filename的value,10是filename="的長度  //通過后臺調試我發現filename=后加的是帶著雙引號的路徑名，在獲取路徑名時不需要分號所以在分離時就將分號也分離掉了  String filename = reqBody.substring(reqBody.indexOf("filename=/"") + 10);  //找到文件名這行的末尾，過濾掉對于獲取文件名而言的無用信息  filename = filename.substring(0, filename.indexOf("/n"));  //獲取不包含路徑名的文件名  filename = filename.substring(filename.lastIndexOf("//") + 1, filename.lastIndexOf("/""));  //此時后臺打印分離路徑后的文件名并將其作為返回值返回  System.out.println(filename);  return filename; } //取得文件開始和結束位置 private Position getFilePosition(HttpServletRequest request, String textBody) throws IOException {  //取得文件區段邊界信息  String contentType = request.getContentType();  String boundaryText = contentType.substring(    contentType.lastIndexOf("=") + 1, contentType.length());  //取得實際上傳文件的起始與結束位置  int pos = textBody.indexOf("filename=/"");  pos = textBody.indexOf("/n", pos) + 1;  pos = textBody.indexOf("/n", pos) + 1;  pos = textBody.indexOf("/n", pos) + 1;  int boundaryLoc = textBody.indexOf(boundaryText, pos) - 4;  int begin = ((textBody.substring(0, pos)).getBytes("ISO-8859-1")).length;  int end = ((textBody.substring(0, boundaryLoc)).getBytes("ISO-8859-1")).length;  return new Position(begin, end); } //輸出至文件 private void writeTo(String filename, byte[] body, Position p) throws IOException {  //默認上傳的文件是在F://javaeeAroundFiles目錄下  FileOutputStream fos = new FileOutputStream("F://javaeeAroundFiles//later//" + filename);  fos.write(body, p.begin, (p.end - p.begin));  fos.flush();  fos.close(); }}

二.使用getPart()和getInputStream()

Demo2

//HTML代碼塊<!-- 該HTML供uploadPartDemo和uploadPartDemo2共同使用，使用時通過更改body的form的action屬性值控制 --><!DOCTYPE html><html> <head>  <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">  <title></title> </head> <body>  <form action="uploadPhoto" method="post"  enctype="multipart/form-data">  上傳相片：<input type="file" name="photo" /><br><br>  <input type="submit" value="上傳" name="upload" />  </form> </body></html>

//uploadPhotoDemo.javaimport java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;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;//Servlet implementation class uploadPartDemo//Tomcat中必須設置@MutipartConfig標注才能使用getPart()相關API@MultipartConfig@WebServlet("/uploadPhoto")public class uploadPartDemo extends HttpServlet { private static final long serialVersionUID = 1L; //@see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  // TODO Auto-generated method stub  //getPart()獲取Part對象  Part part = request.getPart("photo");  String filename = getFilename(part);  writeTo(filename, part); } private String getFilename(Part part) {  String header = part.getHeader("Content-Disposition");  //獲取完整路徑  String filename = header.substring(header.indexOf("filename=/"") + 10, header.lastIndexOf("/""));  //filename after substring is: F:/Entertainment/pictures/e5e893df874df44d99f06bc52504a65c.jpg  System.out.println("filename after substring is: " + filename);  //獲取文件名  filename = filename.substring(filename.lastIndexOf("//") + 1);  //filename after 2 substring is: e5e893df874df44d99f06bc52504a65c.jpg  System.out.println("filename after 2 substring is: " + filename);  return filename; } private void writeTo(String filename, Part part) throws IOException, FileNotFoundException {  InputStream is = part.getInputStream();  FileOutputStream fos = new FileOutputStream("F://javaeeAroundFiles//later//" + filename);  byte[] buffer = new byte[1024];  int length = -1;  while((length = is.read(buffer)) != -1) {   fos.write(buffer, 0, length);  }  is.close();  fos.close(); }}

這個Demo和第一個代碼最大的區別就是，通過getPart()方法獲得了Part對象，通過part對象的getHeader()方法指定標頭獲得對應的值。

在Tomcat中要在Servlet上設置@MultipartConfig才能取得Part對象，否則getPart會得到null

@MultipartConfig含有的屬性如下：

fileSizeThreshold：整數值設置，若上傳文件大小超過設置門檻，則先寫入緩存文件，默認值為0
location：字符串設置，設置寫入文件時的目錄，使用時與write方法一起使用，下一個Demo中演示如何使用，默認是空字符串
maxFileSize：限制上傳文件大小，默認-1L即無限制
maxRequestSize：限制multipart/form-data請求個數，默認值為-1L

Demo3

使用Part的write方法進行文件的寫入，HTML文件查看Demo2注釋部分

//uploadPhotoDemo2.javaimport java.io.IOException;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;//Servlet implementation class uploadPartDemo2//設置屬性，這里的最后一級不用分隔符，可以與Demo2中writeTo方法的路徑做一下對比@MultipartConfig(location="F://javaeeAroundFiles//later")@WebServlet("/uploadPhoto2")public class uploadPartDemo2 extends HttpServlet { private static final long serialVersionUID = 1L; //@see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) protected void doPost(HttpServletRequest request, HttpServletResponse response)   throws ServletException, IOException {  //文件名中可能有中文字符所以進行編碼設置，使用setCharacterEncoding()方法  request.setCharacterEncoding("UTF-8");  Part part = request.getPart("photo");  String filename = getFilename(part);  //使用Part的write方法，寫入location指定路徑  part.write(filename); } //獲取文件名與Demo2相同不放代碼 private String getFilename(Part part) {}}

若要實現同時上傳多個文件則可以使用getParts()方法，獲取到的Part對象被保存在一個Collection中

Demo4

<!-- 該HTML是三個input選框，選擇三個文件 --><!DOCTYPE html><html> <head>  <meta http-equiv="Content-Type"    content="text/html; charset=UTF-8">  <title></title> </head> <body>  <form action="uploadParts" method="post"   enctype="multipart/form-data">   文件1：<input type="file" name="file1" value="" /><br>   文件2：<input type="file" name="file2" value="" /><br>   文件3：<input type="file" name="file3" value="" /><br><br>   <input type="submit" value="上傳" name="upload" />  </form> </body></html>

import java.io.IOException;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;//Servlet implementation class uploadPartsDemo@MultipartConfig(location="F://javaeeAroundFiles//later")@WebServlet("/uploadParts")public class uploadPartsDemo extends HttpServlet { private static final long serialVersionUID = 1L; //@see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) protected void doPost(HttpServletRequest request, HttpServletResponse response)   throws ServletException, IOException {  request.setCharacterEncoding("UTF-8");  //使用foreach遍歷獲取每一個Part對象  for(Part part : request.getParts()) {   if(part.getName().startsWith("file")) {    String filename = getFilename(part);    part.write(filename);   }  } } //與之前的getFilename()方法相同 private String getFilename(Part part) {}

總結

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