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Last Published: 18 January 2008
| Version: 1.2.1
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<h5>Commons FileUpload</h5>
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<div class="section"><h2><a name="Using_FileUpload"></a>Using FileUpload</h2><p> FileUpload can be used in a number of different ways, depending upon the requirements of your application. In the simplest case, you will call a single method to parse the servlet request, and then process the list of items as they apply to your application. At the other end of the scale, you might decide to customize FileUpload to take full control of the way in which individual items are stored; for example, you might decide to stream the content into a database. </p><p> Here, we will describe the basic principles of FileUpload, and illustrate some of the simpler - and most common - usage patterns. Customization of FileUpload is described <a href="customizing.html">elsewhere</a>. </p><p> FileUpload depends on Commons IO, so make sure you have the version mentioned on the <a href="dependencies.html">dependencies page</a> in your classpath before continuing. </p></div><div class="section"><h2><a name="How_it_works"></a>How it works</h2><p> A file upload request comprises an ordered list of <em>items</em> that are encoded according to <a class="externalLink" href="http://www.ietf.org/rfc/rfc1867.txt">RFC 1867</a>, "Form-based File Upload in HTML". FileUpload can parse such a request and provide your application with a list of the individual uploaded items. Each such item implements the <code>FileItem</code> interface, regardless of its underlying implementation. </p><p> This page describes the traditional API of the commons fileupload library. The traditional API is a convenient approach. However, for ultimate performance, you might prefer the faster <a href="streaming.html">Streaming API</a>. </p><p> Each file item has a number of properties that might be of interest for your application. For example, every item has a name and a content type, and can provide an <code>InputStream</code> to access its data. On the other hand, you may need to process items differently, depending upon whether the item is a regular form field - that is, the data came from an ordinary text box or similar HTML field - or an uploaded file. The <code>FileItem</code> interface provides the methods to make such a determination, and to access the data in the most appropriate manner. </p><p> FileUpload creates new file items using a <code>FileItemFactory</code>. This is what gives FileUpload most of its flexibility. The factory has ultimate control over how each item is created. The factory implementation that currently ships with FileUpload stores the item's data in memory or on disk, depending on the size of the item (i.e. bytes of data). However, this behavior can be customized to suit your application. </p></div><div class="section"><h2><a name="Servlets_and_Portlets"></a>Servlets and Portlets</h2><p> Starting with version 1.1, FileUpload supports file upload requests in both servlet and portlet environments. The usage is almost identical in the two environments, so the remainder of this document refers only to the servlet environment. </p><p> If you are building a portlet application, the following are the two distinctions you should make as you read this document: <ul><li> Where you see references to the <code>ServletFileUpload</code> class, substitute the <code>PortletFileUpload</code> class. </li><li> Where you see references to the <code>HttpServletRequest</code> class, substitute the <code>ActionRequest</code> class. </li></ul></p></div><div class="section"><h2><a name="Parsing_the_request"></a>Parsing the request</h2><p> Before you can work with the uploaded items, of course, you need to parse the request itself. Ensuring that the request is actually a file upload request is straightforward, but FileUpload makes it simplicity itself, by providing a static method to do just that. </p><div class="source"><pre>// Check that we have a file upload requestboolean isMultipart = ServletFileUpload.isMultipartContent(request);</pre></div><p> Now we are ready to parse the request into its constituent items. </p><div class="section"><h3><a name="The_simplest_case"></a>The simplest case</h3><p> The simplest usage scenario is the following: <ul><li> Uploaded items should be retained in memory as long as they are reasonably small.⌨️ 快捷键说明
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