无法通过servlet代码在tomcat服务器上上传文件

Question

我一直试图通过servlet将文件上传到Tomcat服务器，但没有成功。我可以创建一个目录，但不知何故servlet代码并没有在"上传"目录中创建文件。

Android中的Java代码：

public void upLoad()
{

String exsistingFileName = path+"//"+"test123.txt";
String lineEnd = "rn";
String twoHyphens = "--";
String boundary = "*****";
try {
// ------------------ CLIENT REQUEST
Log.e(Tag, "Inside second Method");
FileInputStream fileInputStream = new FileInputStream(new File(
exsistingFileName));
// open a URL connection to the Servlet
URL url = new URL(urlString);
// Open a HTTP connection to the URL
conn = (HttpURLConnection) url.openConnection();
// Allow Inputs
conn.setDoInput(true);
// Allow Outputs
conn.setDoOutput(true);
// Don't use a cached copy.
conn.setUseCaches(false);
// Use a post method.
conn.setRequestMethod("POST");
conn.setRequestProperty("Connection", "Keep-Alive");
conn.setRequestProperty("Content-Type",
"multipart/form-data;boundary=" + boundary);

DataOutputStream dos = new DataOutputStream(conn.getOutputStream());
dos.writeBytes(twoHyphens + boundary + lineEnd);
dos.writeBytes("Content-Disposition: post-data; name=uploadedfile;filename="
+ exsistingFileName + "" + lineEnd);
dos.writeBytes(lineEnd);
Log.e(Tag, "Headers are written");
// create a buffer of maximum size
int bytesAvailable = fileInputStream.available();
int maxBufferSize = 1000;
// int bufferSize = Math.min(bytesAvailable, maxBufferSize);
byte[] buffer = new byte[bytesAvailable];
// read file and write it into form...
int bytesRead = fileInputStream.read(buffer, 0, bytesAvailable);
while (bytesRead > 0) {
dos.write(buffer, 0, bytesAvailable);
bytesAvailable = fileInputStream.available();
bytesAvailable = Math.min(bytesAvailable, maxBufferSize);
bytesRead = fileInputStream.read(buffer, 0, bytesAvailable);
}
// send multipart form data necesssary after file data...
dos.writeBytes(lineEnd);
dos.writeBytes(twoHyphens + boundary + twoHyphens + lineEnd);
// close streams
Log.e(Tag, "File is written");
fileInputStream.close();
dos.flush();
dos.close();
} catch (MalformedURLException ex) {
Log.e(Tag, "error: " + ex.getMessage(), ex);
}
catch (IOException ioe) {
Log.e(Tag, "error: " + ioe.getMessage(), ioe);
}
try {
BufferedReader rd = new BufferedReader(new InputStreamReader(conn
.getInputStream()));
String line;
while ((line = rd.readLine()) != null) {
Log.e("Dialoge Box", "Message: " + line);
}
rd.close();
} catch (IOException ioex) {
Log.e("MediaPlayer", "error: " + ioex.getMessage(), ioex);
}
}

Tomcat服务器上的Servlet代码：

import java.io.File;
import java.io.IOException;
import java.util.Iterator;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
/**
* Servlet implementation class UploadServlet
*/
public class UploadServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
private static final String UPLOAD_DIRECTORY = "upload";
private static final int THRESHOLD_SIZE = 1024 * 1024 * 3; // 3MB
private static final int MAX_FILE_SIZE = 1024 * 1024 * 40; // 40MB
private static final int REQUEST_SIZE = 1024 * 1024 * 50; // 50MB
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
*      response)
*/
protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
// checks if the request actually contains upload file
if (!ServletFileUpload.isMultipartContent(request)) {
// if not, we stop here
return;
}
// configures some settings
DiskFileItemFactory factory = new DiskFileItemFactory();
factory.setSizeThreshold(THRESHOLD_SIZE);
factory.setRepository(new File(System.getProperty("java.io.tmpdir")));
ServletFileUpload upload = new ServletFileUpload(factory);
upload.setFileSizeMax(MAX_FILE_SIZE);
upload.setSizeMax(REQUEST_SIZE);
// constructs the directory path to store upload file
String uploadPath = getServletContext().getRealPath("")
+ File.separator + UPLOAD_DIRECTORY;
// creates the directory if it does not exist
File uploadDir = new File(uploadPath);
if (!uploadDir.exists()) {
uploadDir.mkdir();   //I can see the created directory...but nothing happens after that....No error message display after creating directory
}
try {
// parses the request's content to extract file data
List formItems = upload.parseRequest(request);
Iterator iter = formItems.iterator();
// iterates over form's fields
while (iter.hasNext()) {
FileItem item = (FileItem) iter.next();
// processes only fields that are not form fields
if (!item.isFormField()) {
String fileName = new File(item.getName()).getName();
String filePath = uploadPath + File.separator + fileName;
File storeFile = new File(filePath);
// saves the file on disk
item.write(storeFile);
}
}
request.setAttribute("message", "Upload has been done successfully!");
} catch (Exception ex) {
request.setAttribute("message", "There was an error: " + ex.getMessage());
}
getServletContext().getRequestDispatcher("/message.jsp").forward(request,         response);
}
}

我在服务器上的文件结构是：

/webapps/
demo/
upload/ - The file I'm trying to create (test123.txt) should be inside this folder, but it's not.
WEB-INF/
classes/ - UploadServlet.class
lib/ - commons IO and upload jars

Answer 1

您的Content-Disposition标头错误。它说post-data，而在multipart/form-data的情况下它必须是form-data。在您的客户端中相应地进行修复：

dos.writeBytes("Content-Disposition: form-data; name=uploadedfile;filename="
+ exsistingFileName + "" + lineEnd);

另请参阅：

• 使用java.net.URLConnection激发和处理HTTP请求

---

与具体问题无关将上传的文件存储在Web应用程序的部署文件夹中绝对是个坏主意。每当你重新部署新版本的web应用程序时，它们都会丢失，原因很简单，到目前为止上传的所有文件肯定都不包含在原始WAR中。将它们存储在部署文件夹之外的其他位置。只是永远不要使用getRealPath()，它只会导致糟糕的实践。

此外，FileInputStream#available()绝对不会按照您在代码中的想法执行操作。去掉它，只需在具有固定缓冲区大小(例如10KB)的for循环中执行通常的读写操作。

此外，在这里使用DataOutputStream也很可怕。它有不同的用途(创建.dat文件)，在这个特定的结构中，存在与字符编码相关的问题的巨大风险。只需使用PrintWriter，用指定的字符集将其包裹在OutputStreamWriter周围。请注意，上面的"另请参阅"链接中显示了一个完整的示例。