找了二篇介紹比較好的作法可參考以下二篇：
Multipart form upload on Android
Useful Code of the Day: Multipart Form File Upload
Useful Code of the Day: Multipart Form File Upload
So, you want to upload files to your web server, do ya? Well, I've seen this topic posted a few times in the last month or so and many of the response I've seen here haven't included definitive answers. Of course, the actual problems vary, but ultimately, a bunch of people want to do file upload from an applet or application to an existing file upload script (CGI, PHP, JSP, etc.) on a web server. And invariably, there are problems with formatting the HTTP request to get things working.
Well, I had a need to do the same thing. I realize there are other solutions out there, such as some sample code that comes with Jakarta Commons Upload. But since we all like reusable code, and we also all seem to like reinventing wheels, here's my go at it: MultiPartFormOutputStream!
MultiPartFormOutputStream is a specialized OutputStream-like class. You create your URLConnection to the server (a static method included can do this for a URL for you, as some of the settings, doInput and doOutput specifically, seem to confuse people). Then get the OutputStream from it and create a boundary string (a static method to create one is provided as well) and pass them to the constructor. Now you have a MultiPartFormOutputStream which you can use to write form fields like text fields, checkboxes, etc., as well as write file data (from Files, InputStreams or raw bytes).
There are some convenience methods for writing primative type values as well as strings, but any higher level objects (aside from Files or InputStreams) aren't supported. (You can always serialize and pass the raw bytes.)
Sample usage code is below. Also, any recommendations for improvement are requested. The code was tested with the Jakarta Struts.
import java.io.*;
import java.net.*;
/**
* MultiPartFormOutputStream is used to write
* "multipart/form-data" to a java.net.URLConnection for
* POSTing. This is primarily for file uploading to HTTP servers.
*
* @since JDK1.3
*/
public class MultiPartFormOutputStream {
/**
* The line end characters.
*/
private static final String NEWLINE = "\r\n";
/**
* The boundary prefix.
*/
private static final String PREFIX = "--";
/**
* The output stream to write to.
*/
private DataOutputStream out = null;
/**
* The multipart boundary string.
*/
private String boundary = null;
/**
* Creates a new MultiPartFormOutputStream object using
* the specified output stream and boundary. The boundary is required
* to be created before using this method, as described in the
* description for the getContentType(String) method.
* The boundary is only checked for null or empty string,
* but it is recommended to be at least 6 characters. (Or use the
* static createBoundary() method to create one.)
*
* @param os the output stream
* @param boundary the boundary
* @see #createBoundary()
* @see #getContentType(String)
*/
public MultiPartFormOutputStream(OutputStream os, String boundary) {
if(os == null) {
throw new IllegalArgumentException("Output stream is required.");
}
if(boundary == null || boundary.length() == 0) {
throw new IllegalArgumentException("Boundary stream is required.");
}
this.out = new DataOutputStream(os);
this.boundary = boundary;
}
/**
* Writes an boolean field value.
*
* @param name the field name (required)
* @param value the field value
* @throws java.io.IOException on input/output errors
*/
public void writeField(String name, boolean value)
throws java.io.IOException {
writeField(name, new Boolean(value).toString());
}
/**
* Writes an double field value.
*
* @param name the field name (required)
* @param value the field value
* @throws java.io.IOException on input/output errors
*/
public void writeField(String name, double value)
throws java.io.IOException {
writeField(name, Double.toString(value));
}
/**
* Writes an float field value.
*
* @param name the field name (required)
* @param value the field value
* @throws java.io.IOException on input/output errors
*/
public void writeField(String name, float value)
throws java.io.IOException {
writeField(name, Float.toString(value));
}
/**
* Writes an long field value.
*
* @param name the field name (required)
* @param value the field value
* @throws java.io.IOException on input/output errors
*/
public void writeField(String name, long value)
throws java.io.IOException {
writeField(name, Long.toString(value));
}
/**
* Writes an int field value.
*
* @param name the field name (required)
* @param value the field value
* @throws java.io.IOException on input/output errors
*/
public void writeField(String name, int value)
throws java.io.IOException {
writeField(name, Integer.toString(value));
}
/**
* Writes an short field value.
*
* @param name the field name (required)
* @param value the field value
* @throws java.io.IOException on input/output errors
*/
public void writeField(String name, short value)
throws java.io.IOException {
writeField(name, Short.toString(value));
}
/**
* Writes an char field value.
*
* @param name the field name (required)
* @param value the field value
* @throws java.io.IOException on input/output errors
*/
public void writeField(String name, char value)
throws java.io.IOException {
writeField(name, new Character(value).toString());
}
/**
* Writes an string field value. If the value is null, an empty string
* is sent ("").
*
* @param name the field name (required)
* @param value the field value
* @throws java.io.IOException on input/output errors
*/
public void writeField(String name, String value)
throws java.io.IOException {
if(name == null) {
throw new IllegalArgumentException("Name cannot be null or empty.");
}
if(value == null) {
value = "";
}
/*
--boundary\r\n
Content-Disposition: form-data; name=""\r\n
\r\n
\r\n
*/
// write boundary
out.writeBytes(PREFIX);
out.writeBytes(boundary);
out.writeBytes(NEWLINE);
// write content header
out.writeBytes("Content-Disposition: form-data; name=\"" + name + "\"");
out.writeBytes(NEWLINE);
out.writeBytes(NEWLINE);
// write content
out.writeBytes(value);
out.writeBytes(NEWLINE);
out.flush();
}
/**
* Writes a file's contents. If the file is null, does not exists, or
* is a directory, a java.lang.IllegalArgumentException
* will be thrown.
*
* @param name the field name
* @param mimeType the file content type (optional, recommended)
* @param file the file (the file must exist)
* @throws java.io.IOException on input/output errors
*/
public void writeFile(String name, String mimeType, File file)
throws java.io.IOException {
if(file == null) {
throw new IllegalArgumentException("File cannot be null.");
}
if(!file.exists()) {
throw new IllegalArgumentException("File does not exist.");
}
if(file.isDirectory()) {
throw new IllegalArgumentException("File cannot be a directory.");
}
writeFile(name, mimeType, file.getCanonicalPath(), new FileInputStream(file));
}
/**
* Writes a input stream's contents. If the input stream is null, a
* java.lang.IllegalArgumentException will be thrown.
*
* @param name the field name
* @param mimeType the file content type (optional, recommended)
* @param fileName the file name (required)
* @param is the input stream
* @throws java.io.IOException on input/output errors
*/
public void writeFile(String name, String mimeType,
String fileName, InputStream is)
throws java.io.IOException {
if(is == null) {
throw new IllegalArgumentException("Input stream cannot be null.");
}
if(fileName == null || fileName.length() == 0) {
throw new IllegalArgumentException("File name cannot be null or empty.");
}
/*
--boundary\r\n
Content-Disposition: form-data; name=""; filename=""\r\n
Content-Type: \r\n
\r\n
\r\n
*/
// write boundary
out.writeBytes(PREFIX);
out.writeBytes(boundary);
out.writeBytes(NEWLINE);
// write content header
out.writeBytes("Content-Disposition: form-data; name=\"" + name +
"\"; filename=\"" + fileName + "\"");
out.writeBytes(NEWLINE);
if(mimeType != null) {
out.writeBytes("Content-Type: " + mimeType);
out.writeBytes(NEWLINE);
}
out.writeBytes(NEWLINE);
// write content
byte[] data = new byte[1024];
int r = 0;
while((r = is.read(data, 0, data.length)) != -1) {
out.write(data, 0, r);
}
// close input stream, but ignore any possible exception for it
try {
is.close();
} catch(Exception e) {}
out.writeBytes(NEWLINE);
out.flush();
}
/**
* Writes the given bytes. The bytes are assumed to be the contents
* of a file, and will be sent as such. If the data is null, a
* java.lang.IllegalArgumentException will be thrown.
*
* @param name the field name
* @param mimeType the file content type (optional, recommended)
* @param fileName the file name (required)
* @param data the file data
* @throws java.io.IOException on input/output errors
*/
public void writeFile(String name, String mimeType,
String fileName, byte[] data)
throws java.io.IOException {
if(data == null) {
throw new IllegalArgumentException("Data cannot be null.");
}
if(fileName == null || fileName.length() == 0) {
throw new IllegalArgumentException("File name cannot be null or empty.");
}
/*
--boundary\r\n
Content-Disposition: form-data; name=""; filename=""\r\n
Content-Type: \r\n
\r\n
\r\n
*/
// write boundary
out.writeBytes(PREFIX);
out.writeBytes(boundary);
out.writeBytes(NEWLINE);
// write content header
out.writeBytes("Content-Disposition: form-data; name=\"" + name +
"\"; filename=\"" + fileName + "\"");
out.writeBytes(NEWLINE);
if(mimeType != null) {
out.writeBytes("Content-Type: " + mimeType);
out.writeBytes(NEWLINE);
}
out.writeBytes(NEWLINE);
// write content
out.write(data, 0, data.length);
out.writeBytes(NEWLINE);
out.flush();
}
/**
* Flushes the stream. Actually, this method does nothing, as the only
* write methods are highly specialized and automatically flush.
*
* @throws java.io.IOException on input/output errors
*/
public void flush() throws java.io.IOException {
// out.flush();
}
/**
* Closes the stream.
*
* NOTE: This method MUST be called to finalize the
* multipart stream.
*
* @throws java.io.IOException on input/output errors
*/
public void close() throws java.io.IOException {
// write final boundary
out.writeBytes(PREFIX);
out.writeBytes(boundary);
out.writeBytes(PREFIX);
out.writeBytes(NEWLINE);
out.flush();
out.close();
}
/**
* Gets the multipart boundary string being used by this stream.
*
* @return the boundary
*/
public String getBoundary() {
return this.boundary;
}
/**
* Creates a new java.net.URLConnection object from the
* specified java.net.URL. This is a convenience method
* which will set the doInput, doOutput,
* useCaches and defaultUseCaches fields to
* the appropriate settings in the correct order.
*
* @return a java.net.URLConnection object for the URL
* @throws java.io.IOException on input/output errors
*/
public static URLConnection createConnection(URL url)
throws java.io.IOException {
URLConnection urlConn = url.openConnection();
if(urlConn instanceof HttpURLConnection) {
HttpURLConnection httpConn = (HttpURLConnection)urlConn;
httpConn.setRequestMethod("POST");
}
urlConn.setDoInput(true);
urlConn.setDoOutput(true);
urlConn.setUseCaches(false);
urlConn.setDefaultUseCaches(false);
return urlConn;
}
/**
* Creates a multipart boundary string by concatenating 20 hyphens (-)
* and the hexadecimal (base-16) representation of the current time in
* milliseconds.
*
* @return a multipart boundary string
* @see #getContentType(String)
*/
public static String createBoundary() {
return "--------------------" +
Long.toString(System.currentTimeMillis(), 16);
}
/**
* Gets the content type string suitable for the
* java.net.URLConnection which includes the multipart
* boundary string.
*
* This method is static because, due to the nature of the
* java.net.URLConnection class, once the output stream
* for the connection is acquired, it's too late to set the content
* type (or any other request parameter). So one has to create a
* multipart boundary string first before using this class, such as
* with the createBoundary() method.
*
* @param boundary the boundary string
* @return the content type string
* @see #createBoundary()
*/
public static String getContentType(String boundary) {
return "multipart/form-data; boundary=" + boundary;
}
}
Usage: (try/catch left out to shorten the post a bit)
URL url = new URL("http://www.domain.com/webems/upload.do");
// create a boundary string
String boundary = MultiPartFormOutputStream.createBoundary();
URLConnection urlConn = MultiPartFormOutputStream.createConnection(url);
urlConn.setRequestProperty("Accept", "*/*");
urlConn.setRequestProperty("Content-Type",
MultiPartFormOutputStream.getContentType(boundary));
// set some other request headers...
urlConn.setRequestProperty("Connection", "Keep-Alive");
urlConn.setRequestProperty("Cache-Control", "no-cache");
// no need to connect cuz getOutputStream() does it
MultiPartFormOutputStream out =
new MultiPartFormOutputStream(urlConn.getOutputStream(), boundary);
// write a text field element
out.writeField("myText", "text field text");
// upload a file
out.writeFile("myFile", "text/plain", new File("C:\\test.txt"));
// can also write bytes directly
//out.writeFile("myFile", "text/plain", "C:\\test.txt",
// "This is some file text.".getBytes("ASCII"));
out.close();
// read response from server
BufferedReader in = new BufferedReader(
new InputStreamReader(urlConn.getInputStream()));
String line = "";
while((line = in.readLine()) != null) {
System.out.println(line);
}
in.close();
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