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File Upload

The Struts 2 framework provides built-in support for processing file uploads that conform to RFC 1867,
“Form-based File Upload in HTML”. When correctly configured the framework will pass uploaded file(s) into your Action
class. Support for individual and multiple file uploads are provided. When a file is uploaded it will typically be
stored in a temporary directory. Uploaded files should be processed or moved by your Action class to ensure the data is
not lost. Be aware that servers may have a security policy in place that prohibits you from writing to directories other
than the temporary directory and the directories that belong to your web application.

Dependencies

The Struts 2 framework leverages the Commons FileUpload library as a based library to support file upload in the framework.
The library is included in a base Struts 2 distribution.

Basic Usage

The org.apache.struts2.interceptor.FileUploadInterceptor class is included as part of the defaultStack. As long as
the required libraries are added to your project you will be able to take advantage of the Struts 2 file upload
capability. Configure an Action mapping for your Action class as you typically would.

Example action mapping:

<action
 name=
"doUpload"
 class=
"com.example.UploadAction"
>
    <result
 name=
"success"
>
good_result.jsp</result>
</action>

A form must be create with a form field of type file, <INPUT type="file" name="upload">. The form used to upload the
file must have its encoding type set
to multipart/form-data, <form action="doUpload" enctype="multipart/form-data" method="post">.
The standard procedure for adding these elements is by using the Struts 2 tag libraries as shown in the following
example:

<s:form
 action=
"doUpload"
 method=
"post"
 enctype=
"multipart/form-data"
>
    <s:file
 name=
"upload"
 label=
"File"
/>
    <s:submit/>
</s:form>

The fileUpload interceptor will use setter injection to insert the uploaded file and related data into your Action
class. For a form field named upload you would provide the three setter methods shown in the following example:

Example Action class:

package
 com.example
;

import
 java.io.File
;

import
 com.opensymphony.xwork2.ActionSupport
;

public
 class
 UploadAction
 extends
 ActionSupport
 {
    private
 File
 file
;
    private
 String
 contentType
;
    private
 String
 filename
;

    public
 void
 setUpload
(
File
 file
)
 {
        this
.
file
 =
 file
;
    }

    public
 void
 setUploadContentType
(
String
 contentType
)
 {
        this
.
contentType
 =
 contentType
;
    }

    public
 void
 setUploadFileName
(
String
 filename
)
 {
        this
.
filename
 =
 filename
;
    }

    public
 String
 execute
()
 {
        //...
        return
 SUCCESS
;
    }
}

The purpose of each one of these methods is described in the table below. Notice that if you have multiple file form
elements with different names you would be required to have another corresponding set of these methods for each file
uploaded.

Method Signature
Description

setX(File file)
The file that contains the content of the uploaded file. This is a temporary file and file.getName() will not return the original name of the file

setXContentType(String contentType)
The mime type of the uploaded file

setXFileName(String fileName)
The actual file name of the uploaded file (not the HTML name)

Uploading Multiple Files

As mentioned in the previous section one technique for uploading multiple files would be to simply have multiple form
input elements of type file all with different names. This would require a number of setter methods that was equal to 3
times the number of files being uploaded. Another option is to use Arrays or java.util.Lists. The following examples are
taken from the Showcase example application that is part sample applications you can download
at http://struts.apache.org/download.cgi. For the Action mapping details
see struts-fileupload.xml in the sample application download.

Uploading Multiple Files using Arrays

multipleUploadUsingArray.jsp Notice all file input types have the same name.

<s:form
 action=
"doMultipleUploadUsingArray"
 method=
"POST"
 enctype=
"multipart/form-data"
>
    <s:file
 label=
"File (1)"
 name=
"upload"
/>
    <s:file
 label=
"File (2)"
 name=
"upload"
/>
    <s:file
 label=
"FIle (3)"
 name=
"upload"
/>
    <s:submit
 cssClass=
"btn btn-primary"
/>
</s:form>

MultipleFileUploadUsingArrayAction.java

public
 class
 MultipleFileUploadUsingArrayAction
 extends
 ActionSupport
 {
    private
 File
[]
 uploads
;
    private
 String
[]
 uploadFileNames
;
    private
 String
[]
 uploadContentTypes
;

    public
 String
 upload
()
 throws
 Exception
 {
        System
.
out
.
println
(
"\n\n upload2"
);
        System
.
out
.
println
(
"files:"
);
        for
 (
File
 u
 :
 uploads
)
 {
            System
.
out
.
println
(
"*** "
 +
 u
 +
 "\t"
 +
 u
.
length
());
        }
        System
.
out
.
println
(
"filenames:"
);
        for
 (
String
 n
 :
 uploadFileNames
)
 {
            System
.
out
.
println
(
"*** "
 +
 n
);
        }
        System
.
out
.
println
(
"content types:"
);
        for
 (
String
 c
 :
 uploadContentTypes
)
 {
            System
.
out
.
println
(
"*** "
 +
 c
);
        }
        System
.
out
.
println
(
"\n\n"
);
        return
 SUCCESS
;
    }

    public
 File
[]
 getUpload
()
 {
        return
 this
.
uploads
;
    }

    public
 void
 setUpload
(
File
[]
 upload
)
 {
        this
.
uploads
 =
 upload
;
    }

    public
 String
[]
 getUploadFileName
()
 {
        return
 this
.
uploadFileNames
;
    }

    public
 void
 setUploadFileName
(
String
[]
 uploadFileName
)
 {
        this
.
uploadFileNames
 =
 uploadFileName
;
    }

    public
 String
[]
 getUploadContentType
()
 {
        return
 this
.
uploadContentTypes
;
    }

    public
 void
 setUploadContentType
(
String
[]
 uploadContentType
)
 {
        this
.
uploadContentTypes
 =
 uploadContentType
;
    }
}

Uploading Multiple Files using Lists

multipleUploadUsingList.jsp Notice all file input types have the same name.

<s:form
 action=
"doMultipleUploadUsingList"
 method=
"POST"
 enctype=
"multipart/form-data"
>
    <s:file
 label=
"File (1)"
 name=
"upload"
/>
    <s:file
 label=
"File (2)"
 name=
"upload"
/>
    <s:file
 label=
"FIle (3)"
 name=
"upload"
/>
    <s:submit
 cssClass=
"btn btn-primary"
/>
</s:form>

MultipleFileUploadUsingListAction.java

public
 class
 MultipleFileUploadUsingListAction
 extends
 ActionSupport
 {
    private
 List
<
File
>
 uploads
 =
 new
 ArrayList
<
File
>();
    private
 List
<
String
>
 uploadFileNames
 =
 new
 ArrayList
<
String
>();
    private
 List
<
String
>
 uploadContentTypes
 =
 new
 ArrayList
<
String
>();

    public
 List
<
File
>
 getUpload
()
 {
        return
 this
.
uploads
;
    }

    public
 void
 setUpload
(
List
<
File
>
 uploads
)
 {
        this
.
uploads
 =
 uploads
;
    }

    public
 List
<
String
>
 getUploadFileName
()
 {
        return
 this
.
uploadFileNames
;
    }

    public
 void
 setUploadFileName
(
List
<
String
>
 uploadFileNames
)
 {
        this
.
uploadFileNames
 =
 uploadFileNames
;
    }

    public
 List
<
String
>
 getUploadContentType
()
 {
        return
 this
.
uploadContentTypes
;
    }

    public
 void
 setUploadContentType
(
List
<
String
>
 contentTypes
)
 {
        this
.
uploadContentTypes
 =
 contentTypes
;
    }

    public
 String
 upload
()
 throws
 Exception
 {
        System
.
out
.
println
(
"\n\n upload1"
);
        System
.
out
.
println
(
"files:"
);
        for
 (
File
 u
 :
 uploads
)
 {
            System
.
out
.
println
(
"*** "
 +
 u
 +
 "\t"
 +
 u
.
length
());
        }
        System
.
out
.
println
(
"filenames:"
);
        for
 (
String
 n
 :
 uploadFileNames
)
 {
            System
.
out
.
println
(
"*** "
 +
 n
);
        }
        System
.
out
.
println
(
"content types:"
);
        for
 (
String
 c
 :
 uploadContentTypes
)
 {
            System
.
out
.
println
(
"*** "
 +
 c
);
        }
        System
.
out
.
println
(
"\n\n"
);
        return
 SUCCESS
;
    }
}

Advanced Configuration

The Struts 2 default.properties file defines several settings that affect the behavior of file uploading. You may find
in necessary to change these values. The names and default values are:

struts.multipart.parser=jakarta
struts.multipart.saveDir=
struts.multipart.maxSize=2097152
struts.multipart.maxFiles=256

Please remember that the struts.multipart.maxSize is the size limit of the whole request, which means when you’re
uploading multiple files, the sum of their size must be below the struts.multipart.maxSize!

In order to change these settings you define a constant in your applications struts.xml file like so:

<struts>
    <constant
 name=
"struts.multipart.maxSize"
 value=
"1000000"
/>
    ...
</struts>

Additionally, the fileUpload interceptor has settings that can be put in place for individual action mappings
by customizing your interceptor stack.

<action
 name=
"doUpload"
 class=
"com.example.UploadAction"
>
    <interceptor-ref
 name=
"basicStack"
/>
    <interceptor-ref
 name=
"fileUpload"
>
        <param
 name=
"allowedTypes"
>
text/plain</param>
    </interceptor-ref>
    <interceptor-ref
 name=
"validation"
/>
    <interceptor-ref
 name=
"workflow"
/>

    <result
 name=
"success"
>
good_result.jsp</result>
</action>

File Size Limits

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:

<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>

Files Number Limit

Since Struts 6.1.2/6.2.0 a new option was added, which uses Commons FileUpload feature to limit how many files can be uploaded
at once, in one request. This option requires to use Commons FileUpload ver. 1.5 at least and by default is set to 256.
To change this value define a constant in struts.xml as follows:

<struts>
    <constant
 name=
"struts.multipart.maxFiles"
 value=
"500"
/>
</struts>

File Types

There are two ways to limit the uploaded file type, decoratively and programmatically. To decoratively limit the file
type a comma separated list of allowedTypes can be specified as a fileUpload interceptor param as shown in the following
example:

<action
 name=
"doUpload"
 class=
"com.example.UploadAction"
>
    <interceptor-ref
 name=
"basicStack"
/>
    <interceptor-ref
 name=
"fileUpload"
>
        <param
 name=
"allowedTypes"
>
image/jpeg,image/gif</param>
    </interceptor-ref>
    <interceptor-ref
 name=
"validation"
/>
    <interceptor-ref
 name=
"workflow"
/>

    <result
 name=
"success"
>
good_result.jsp</result>
</action>

When the uploaded file type does not match one of the MIME types specified a field error will be created as described in
the next section entitled Error Messages. Programmatically limiting the file type means using the information passed in
to your Action class via the setXContentType(String contentType) method. The benefit to this type of approach would be
that it’s more flexible and no interceptor configuration would be needed if file sizes are keep under 2 megs.

Error Messages

If an error occurs several field errors will be added assuming that the action
implements com.opensymphony.xwork2.ValidationAware
or extends com.opensymphony.xwork2.ActionSupport. These error messages are based on several i18n values stored in
struts-messages.properties, a default i18n file processed for all i18n requests. You can override the text of these
messages by providing text for the following keys:

Error Key
Description

struts.messages.error.uploading
A general error that occurs when the file could not be uploaded

struts.messages.error.file.too.large
Occurs when the uploaded file is too large as specified by maximumSize.

struts.messages.error.content.type.not.allowed
Occurs when the uploaded file does not match the expected content types specified

struts.messages.error.file.extension.not.allowed
Occurs when uploaded file has disallowed extension

struts.messages.upload.error.SizeLimitExceededException
Occurs when the upload request (as a whole) exceed configured struts.multipart.maxSize
struts.messages.upload.error.<Exception class SimpleName>
Occurs when any other exception took place during file upload process

Temporary Directories

All uploaded files are saved to a temporary directory by the framework before being passed in to an Action. Depending on
the allowed file sizes it may be necessary to have the framework store these temporary files in an alternate location.
To do this change struts.multipart.saveDir
to the directory where the uploaded files will be placed. If this property is not set it defaults
to javax.servlet.context.tempdir. Keep in mind that on some operating systems, like Solaris, /tmp is memory based
and files stored in that directory would consume an amount of RAM approximately equal to the size of the uploaded file.

Alternate Libraries

The struts.multipart.parser used by the fileUpload interceptor to handle HTTP POST requests, encoded using the
MIME-type multipart/form-data, can be changed out. Currently there are two choices, jakarta and pell. The jakarta
parser is a standard part of the Struts 2 framework needing only its required libraries added to a project. The pell
parser uses Jason Pell’s multipart parser instead of the Commons-FileUpload library. The pell parser is a Struts 2
plugin, for more details see: Pell multipart plugin. There was a third alternative, cos, but it was
removed due to licensing incompatibilities.

As from Struts version 2.3.18 a new implementation of MultiPartRequest was added – JakartaStreamMultiPartRequest. It
can be used to handle large files, see WW-3025 for more details, but
you can simple set

<constant name="struts.multipart.parser" value="jakarta-stream" />

in struts.xml to start using it.

Request validation

The struts.multipart.validationRegex is used to define a RegEx to be used to validate if the incoming request is a
multipart request. The request must use the POST method and match the RegEx, by default the RegEx is defined as
follow:

^multipart/form-data(?:\\s*;\\s*boundary=[0-9a-zA-Z'()+_,\\-./:=?]{1,70})?(?:\\s*;\\s*charset=[a-zA-Z\\-0-9]{3,14})?

Please read RFC1341 the Multipart section for more
details,
existing Struts Multipart parsers support only multipart/form-data content type. This option is available since
Struts 2.3.11.

Disabling file upload support

You can alternatively disable the whole file upload mechanism defining a constant in struts.xml:

<constant
 name=
"struts.multipart.enabled"
 value=
"false"
/>

With this constant in place, Struts will ignore a Content-Type header and will treat each request as an ordinary http
request. This option is available since Struts 2.3.11.