解决MultipartEntity无法获取内容数据问题：Multipart form entity does not implement #getContent()

最近在使用httppost和CloseableHttpClient进行文件上传的时候碰到了问题，就是MultipartEntity无法获取内容数据。报错提示如下：

Exception in thread "main" java.lang.UnsupportedOperationException: Multipart form entity does not implement #getContent()
at org.apache.http.entity.mime.MultipartFormEntity.getContent(MultipartFormEntity.java:92)

下面是MultipartEntity的源码展示：

The MultipartEntity.java example source code

/* * ==================================================================== * 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. * ==================================================================== * * This software consists of voluntary contributions made by many * individuals on behalf of the Apache Software Foundation.  For more * information on the Apache Software Foundation, please see * <http://www.apache.org/>. * */package org.apache.http.entity.mime;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;import java.nio.charset.Charset;import java.util.Iterator;import java.util.List;import java.util.Random;import org.apache.http.annotation.ThreadSafe;import org.apache.http.Header;import org.apache.http.HttpEntity;import org.apache.http.entity.mime.content.ContentBody;import org.apache.http.message.BasicHeader;import org.apache.http.protocol.HTTP;import org.apache.james.mime4j.field.Fields;import org.apache.james.mime4j.message.Message;/** * Multipart/form coded HTTP entity consisting of multiple * body parts.  *  * * @since 4.0 */@ThreadSafepublic class MultipartEntity implements HttpEntity {    /**     * The pool of ASCII chars to be used for generating a multipart boundary.     */    private final static char[] MULTIPART_CHARS =         "-_1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"            .toCharArray();        private final Message message;    private final HttpMultipart multipart;    private final Header contentType;        private long length;    private volatile boolean dirty; // used to decide whether to recalculate length        public MultipartEntity(            HttpMultipartMode mode,             final String boundary,            final Charset charset) {        super();        this.multipart = new HttpMultipart("form-data");        this.contentType = new BasicHeader(                HTTP.CONTENT_TYPE,                generateContentType(boundary, charset));        this.dirty = true;                this.message = new Message();        org.apache.james.mime4j.message.Header header =           new org.apache.james.mime4j.message.Header();        this.message.setHeader(header);        this.multipart.setParent(message);        if (mode == null) {            mode = HttpMultipartMode.STRICT;        }        this.multipart.setMode(mode);        this.message.getHeader().addField(Fields.contentType(this.contentType.getValue()));    }    public MultipartEntity(final HttpMultipartMode mode) {        this(mode, null, null);    }    public MultipartEntity() {        this(HttpMultipartMode.STRICT, null, null);    }    protected String generateContentType(            final String boundary,            final Charset charset) {        StringBuilder buffer = new StringBuilder();        buffer.append("multipart/form-data; boundary=");        if (boundary != null) {            buffer.append(boundary);        } else {            Random rand = new Random();            int count = rand.nextInt(11) + 30; // a random size from 30 to 40            for (int i = 0; i < count; i++) {                buffer.append(MULTIPART_CHARS[rand.nextInt(MULTIPART_CHARS.length)]);            }        }        if (charset != null) {            buffer.append("; charset=");            buffer.append(charset.name());        }        return buffer.toString();    }    public void addPart(final String name, final ContentBody contentBody) {        this.multipart.addBodyPart(new FormBodyPart(name, contentBody));        this.dirty = true;    }      public boolean isRepeatable() {        List<?> parts = this.multipart.getBodyParts();        for (Iterator<?> it = parts.iterator(); it.hasNext(); ) {            FormBodyPart part = (FormBodyPart) it.next();            ContentBody body = (ContentBody) part.getBody();            if (body.getContentLength() < 0) {                return false;            }        }        return true;    }    public boolean isChunked() {        return !isRepeatable();    }    public boolean isStreaming() {        return !isRepeatable();    }    public long getContentLength() {        if (this.dirty) {            this.length = this.multipart.getTotalLength();            this.dirty = false;        }        return this.length;    }    public Header getContentType() {        return this.contentType;    }    public Header getContentEncoding() {        return null;    }    public void consumeContent()        throws IOException, UnsupportedOperationException{        if (isStreaming()) {            throw new UnsupportedOperationException(                    "Streaming entity does not implement #consumeContent()");        }    }    public InputStream getContent() throws IOException, UnsupportedOperationException {        throw new UnsupportedOperationException(                    "Multipart form entity does not implement #getContent()");    }    public void writeTo(final OutputStream outstream) throws IOException {        this.multipart.writeTo(outstream);    }}

那要获取请求的内容怎么办？下面是解决方案：

使用 org.apache.http.entity.mime.MultipartEntity writeTo(java.io.OutputStream) 方法把内容写入到一个 java.io.OutputStream中, 然后把数据转换成 String or byte[]:

// import java.io.ByteArrayOutputStream;// import org.apache.http.entity.mime.MultipartEntity;// ...// MultipartEntity entity = ...;// ...ByteArrayOutputStream out = new ByteArrayOutputStream(entity.getContentLength());// write content to streamentity.writeTo(out);// either convert stream to stringString string = out.toString();// or convert stream to bytesbyte[] bytes = out.toByteArray();

Note: this only works for multipart entities both smaller than 2Gb, the maximum size of a byte array in Java, and small enough to be read into memory.