FileItem

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.fileupload;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.UnsupportedEncodingException;

/**
 * <p> This class represents a file or form item that was received within a
 * <code>multipart/form-data</code> POST request.
 *
 * <p> After retrieving an instance of this class from a {@link
 * org.apache.commons.fileupload.FileUpload FileUpload} instance (see
 * {@link org.apache.commons.fileupload.servlet.ServletFileUpload
 * #parseRequest(javax.servlet.http.HttpServletRequest)}), you may
 * either request all contents of the file at once using {@link #get()} or
 * request an {@link java.io.InputStream InputStream} with
 * {@link #getInputStream()} and process the file without attempting to load
 * it into memory, which may come handy with large files.
 *
 * <p> While this interface does not extend
 * <code>javax.activation.DataSource</code> per se (to avoid a seldom used
 * dependency), several of the defined methods are specifically defined with
 * the same signatures as methods in that interface. This allows an
 * implementation of this interface to also implement
 * <code>javax.activation.DataSource</code> with minimal additional work.
 *
 * @since 1.3 additionally implements FileItemHeadersSupport
 */
public interface FileItem extends FileItemHeadersSupport {

    // ------------------------------- Methods from javax.activation.DataSource

    /**
     * Returns an {@link java.io.InputStream InputStream} that can be
     * used to retrieve the contents of the file.
     *
     * @return An {@link java.io.InputStream InputStream} that can be
     *         used to retrieve the contents of the file.
     *
     * @throws IOException if an error occurs.
     */
     /**
     *返回一个{@link java.io.InputStream InputStream}，它可以是
     *用于检索文件的内容。
     *
     *@return {@link java.io.InputStream InputStream}可以是
     *用于检索文件的内容。
     *
     *如果发生错误，则抛出IOException。
     */
    InputStream getInputStream() throws IOException;

    /**
     * Returns the content type passed by the browser or <code>null</code> if
     * not defined.
     *
     * @return The content type passed by the browser or <code>null</code> if
     *         not defined.
     */
     /**
     *返回浏览器传递的内容类型；如果返回，则为<code> null </code>
     *没有定义的。
     *
     *@return浏览器传递的内容类型；如果为null，则为<code> null </code>
     *        没有定义的。
     */
     // getContentType 方法用于获得上传文件的类型，即表单字段元素描述头属性“Content-Type”的值，如“image/jpeg”。如果FileItem类对象对应的是普通表单字段，该方法将返回null。
    String getContentType();

    /**
     * Returns the original filename in the client's filesystem, as provided by
     * the browser (or other client software). In most cases, this will be the
     * base file name, without path information. However, some clients, such as
     * the Opera browser, do include path information.
     *
     * @return The original filename in the client's filesystem.
     * @throws InvalidFileNameException The file name contains a NUL character,
     *   which might be an indicator of a security attack. If you intend to
     *   use the file name anyways, catch the exception and use
     *   InvalidFileNameException#getName().
     */
     /**
     *返回客户端文件系统中的原始文件名，由
     *浏览器（或其他客户端软件）。在大多数情况下，这将是
     *基本文件名，不包含路径信息。但是，有些客户，例如
     *Opera浏览器，确实包含路径信息。
     *
     *@return客户端文件系统中的原始文件名。
     *@throws InvalidFileNameException文件名包含一个NUL字符，
     *可能表明存在安全攻击。如果你打算
     *始终使用文件名，捕获异常并使用
     *InvalidFileNameException＃getName（）。
     */
     // getName方法用于获得文件上传字段中的文件名。注意IE或FireFox中获取的文件名是不一样的，IE中是绝对路径，FireFox中只是文件名。
    String getName();

    // ------------------------------------------------------- FileItem methods

    /**
     * Provides a hint as to whether or not the file contents will be read
     * from memory.
     *
     * @return <code>true</code> if the file contents will be read from memory;
     *         <code>false</code> otherwise.
     */
     /**
     *提供有关是否读取文件内容的提示
     *从记忆里。
     *
     *@return <code> true </code>如果将从内存中读取文件内容；
     *<code> false </code>否则。
     */
     // isInMemory方法用来判断FileItem对象封装的数据内容是存储在内存中，还是存储在临时文件中，如果存储在内存中则返回true，否则返回false。
    boolean isInMemory();

    /**
     * Returns the size of the file item.
     *
     * @return The size of the file item, in bytes.
     */
    long getSize();

    /**
     * Returns the contents of the file item as an array of bytes.
     *
     * @return The contents of the file item as an array of bytes.
     */
    byte[] get();

    /**
     * Returns the contents of the file item as a String, using the specified
     * encoding.  This method uses {@link #get()} to retrieve the
     * contents of the item.
     *
     * @param encoding The character encoding to use.
     *
     * @return The contents of the item, as a string.
     *
     * @throws UnsupportedEncodingException if the requested character
     *                                      encoding is not available.
     */
    String getString(String encoding) throws UnsupportedEncodingException;

    /**
     * Returns the contents of the file item as a String, using the default
     * character encoding.  This method uses {@link #get()} to retrieve the
     * contents of the item.
     *
     * @return The contents of the item, as a string.
     */
     /**
     *使用默认值以字符串形式返回文件项的内容
     *字符编码。此方法使用{@link #get（）}来检索
     *项目内容。
     *
     *@return项目的内容，以字符串形式。
     */
     /**
     * getString方法用于将FileItem对象中保存的数据流内容以一个字符串返回，它有两个重载的定义形式：
    * public java.lang.String getString()
    * public java.lang.String getString(java.lang.String encoding)
    * throws java.io.UnsupportedEncodingException
    * 前者使用缺省的字符集编码将主体内容转换成字符串，后者使用参数指定的字符集编码将主体内容转换成字符串。如果在读取普通表单字段元素的内容时出现了中文乱码现象，请调用第二个getString方法，并为之传递正确的字符集编码名称。
     */
    String getString();

    /**
     * A convenience method to write an uploaded item to disk. The client code
     * is not concerned with whether or not the item is stored in memory, or on
     * disk in a temporary location. They just want to write the uploaded item
     * to a file.
     * <p>
     * This method is not guaranteed to succeed if called more than once for
     * the same item. This allows a particular implementation to use, for
     * example, file renaming, where possible, rather than copying all of the
     * underlying data, thus gaining a significant performance benefit.
     *
     * @param file The <code>File</code> into which the uploaded item should
     *             be stored.
     *
     * @throws Exception if an error occurs.
     */
     /**
     *一种方便的方法将上传的项目写入磁盘。客户端代码
     *与项目是否存储在内存中无关
     *磁盘在一个临时位置。他们只想写上载的项目
     *到文件。
     *<p>
     *如果多次调用此方法，则不能保证此方法成功
     *同一项目。这允许特定的实现用于
     *例如，在可能的情况下重命名文件，而不是复制所有
     *基础数据，从而获得显着的性能优势。
     *
     *@param file上传项目应放入的<code> File </code>
     *被存储。
     *
     *@throws 如果发生错误，则异常。
     */
     // write方法用于将FileItem对象中保存的主体内容保存到某个指定的文件中。如果FileItem对象中的主体内容是保存在某个临时文件中，该方法顺利完成后，临时文件有可能会被清除。该方法也可将普通表单字段内容写入到一个文件中，但它主要用途是将上传的文件内容保存在本地文件系统中。
    void write(File file) throws Exception;

    /**
     * Deletes the underlying storage for a file item, including deleting any
     * associated temporary disk file. Although this storage will be deleted
     * automatically when the <code>FileItem</code> instance is garbage
     * collected, this method can be used to ensure that this is done at an
     * earlier time, thus preserving system resources.
     */
    void delete();

    /**
     * Returns the name of the field in the multipart form corresponding to
     * this file item.
     *
     * @return The name of the form field.
     */
    /**
     *以对应的多部分形式返回字段名称
     *此文件项。
     *
     *@return表单字段的名称。
     */
     // getFieldName方法用于返回表单标签name属性的值。如上例中<input type="text" name="column" />的value。
    String getFieldName();

    /**
     * Sets the field name used to reference this file item.
     *
     * @param name The name of the form field.
     */
    void setFieldName(String name);

    /**
     * Determines whether or not a <code>FileItem</code> instance represents
     * a simple form field.
     *
     * @return <code>true</code> if the instance represents a simple form
     *         field; <code>false</code> if it represents an uploaded file.
     */
     /**
     *确定<code> FileItem </code>实例是否代表
     *一个简单的表单字段。
     *
     *@return <code> true </code>（如果实例代表一种简单形式）
     *栏位； <code> false </code>（如果它代表上传的文件）。
     */
     // isFormField方法用于判断FileItem类对象封装的数据是一个普通文本表单字段，还是一个文件表单字段，如果是普通表单字段则返回true，否则返回false。因此，可以使用该方法判断是否为普通表单域，还是文件上传表单域。
    boolean isFormField();

    /**
     * Specifies whether or not a <code>FileItem</code> instance represents
     * a simple form field.
     *
     * @param state <code>true</code> if the instance represents a simple form
     *              field; <code>false</code> if it represents an uploaded file.
     */
    void setFormField(boolean state);

    /**
     * Returns an {@link java.io.OutputStream OutputStream} that can
     * be used for storing the contents of the file.
     *
     * @return An {@link java.io.OutputStream OutputStream} that can be used
     *         for storing the contensts of the file.
     *
     * @throws IOException if an error occurs.
     */
    OutputStream getOutputStream() throws IOException;

}