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Thursday, August 13, 2009

Uploading Files with a Multipart POST

Uploading Files with a Multipart POST

11.9.1. Problem

You need to upload a file or a set of files with an HTTP multipart POST.

11.9.2. Solution

Create a MultipartPostMethod and add File objects as parameters using addParameter( ) and addPart( ). The MultipartPostMethod creates a request with a Content-Type header of multipart/form-data, and each part is separated by a boundary. The following example sends two files in an HTTP multipart POST:

               import org.apache.commons.httpclient.HttpClient;

import org.apache.commons.httpclient.HttpException;

import org.apache.commons.httpclient.methods.MultipartPostMethod;

import org.apache.commons.httpclient.methods.multipart.FilePart;

HttpClient client = new HttpClient( );


// Create POST method

String weblintURL = "";

MultipartPostMethod method =

    new MultipartPostMethod( weblintURL );

File file = new File( "data", "test.txt" );

               File file2 = new File( "data", "sample.txt" );

               method.addParameter("test.txt", file );

               method.addPart( new FilePart( "sample.txt", file2, "text/plain",

"ISO-8859-1" ) );

// Execute and print response

client.executeMethod( method );

String response = method.getResponseBodyAsString( );

System.out.println( response );

method.releaseConnection( );

Two File objects are added to the MultipartPostMethod using two different methods. The first method, addParameter( ), adds a File object and sets the file name to test.txt. The second method, addPart(), adds a FilePart object to the MultipartPostMethod. Both files are sent in the request separated by a part boundary, and the script echoes the location and type of both files on the server:

<h3>Form input</h3>


sample.txt = /tmp/CGI14480.4 sample.txt {text/plain; charset=ISO-8859-1}

test.txt = /tmp/CGI14480.2 test.txt {application/octet-stream;



11.9.3. Discussion

Adding a part as a FilePart object allows you to specify the Multipurpose Internet Main Extensions (MIME) type and the character set of the part. In this example, the sample.txt file is added with a text/plain MIME type and an ISO-8859-1 character set. If a File is added to the method using addParameter( ) or setParameter( ), it is sent with the default application/octet-stream type and the default ISO-8859-1 character set.

When HttpClient executes the MultipartPostMethod created in the previous example, the following request is sent to the server. The Content-Type header is multipart/form-data, and an arbitrary boundary is created to delineate multiple parts being sent in the request:

POST /cgi-bin/cgi.tcl/echo.cgi HTTP/1.1

User-Agent: Jakarta Commons-HttpClient/3.0final


Content-Length: 498

Content-Type: multipart/form-data; boundary=----------------31415926535



Content-Disposition: form-data; name=test.txt; filename=test.txt

Content-Type: application/octet-stream; charset=ISO-8859-1

Content-Transfer-Encoding: binary

This is a test.


Content-Disposition: form-data; name=sample.txt; filename=sample.txt

Content-Type: text/plain; charset=ISO-8859-1

Content-Transfer-Encoding: binary

This is a sample


Each part contains a Content-Disposition header to name the part and a Content-Type header to classify the part with a MIME type and character set.


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