Código:
There are two separate file size limits. First is struts.multipart.maxSize which comes from the Struts 2 default.properties file. This setting exists for security reasons to prohibit a malicious user from uploading extremely large files to file up your servers disk space. This setting defaults to approximately 2 megabytes and should be adjusted to the maximum size file (2 gigs max) that your will need the framework to receive. If you are uploading more than one file on a form the struts.multipart.maxSize applies to the combined total, not the individual file sizes The other setting, maximumSize, is an interceptor setting that is used to ensure a particular Action does not receive a file that is too large. .Notice the locations of both settings in the following example:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.0.dtd">
<struts>
<constant name="struts.multipart.maxSize" value="1000000" />
<action name="doUpload" class="com.example.UploadAction">
<interceptor-ref name="basicStack"/>
<interceptor-ref name="fileUpload">
<param name="maximumSize">500000</param>
</interceptor-ref>
<interceptor-ref name="validation"/>
<interceptor-ref name="workflow"/>
<result name="success">good_result.jsp</result>
</action>
</struts>
En el default.properties se fija a 2Mb por defecto el valor total máximo de subida por archivo. Cámbialo y listo.
Saludos