java使用httpclient时，获取HttpPost对象中的入参

 在某些特殊情况下，需要获取HttpPost对象中的参数，demo如下

    public static HttpResponse test( HttpPost post ) throws IOException{

        /**
         * 入参是HttpPost，在该方法中想根据HttpPost中的参数做一些逻辑，这时候就需要想办法获取到HttpPost中的入参
         */
        HttpEntity entity = post.getEntity();      //代码一

//      InputStream inputStream = entity.getContent();      //方法一
//      System.out.println(EntityUtils.toString(entity));   //方法二
        //获取入参的方法
        MyHttpEntityUnil.test(entity);   //方法三

        HttpClient httpclient = new DefaultHttpClient();
        return httpclient.execute(post);
    }


    public static void main(String[] args) throws ParseException, IOException {

        ContentType contentType = ContentType.create("text/plain", Consts.UTF_8);
        MultipartEntityBuilder builder = MultipartEntityBuilder.create();

        builder.addTextBody("aaa", "bbb", contentType);

        HttpEntity requestEntity = builder.build();

        HttpPost post = new HttpPost("http://127.0.0.1:8080/index");
        post.setEntity(requestEntity);

        test(post);

    }

常规思路如demo中的方法一、方法二都是通过获取HttpEntity的输入流（InputStream），但是会抛一个异常，原因是该处使用的HttpEntity是实现类MultipartFormEntity，而MultipartFormEntity并没有实现接口HttpEntity的getContent()方法。这时候就要转变思路，查看MultipartFormEntity的源码，如下

/*
 * ====================================================================
 * 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 org.apache.http.Header;
import org.apache.http.HttpEntity;
import org.apache.http.message.BasicHeader;
import org.apache.http.protocol.HTTP;

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

class MultipartFormEntity implements HttpEntity {

    private final AbstractMultipartForm multipart;
    private final Header contentType;
    private final long contentLength;

    MultipartFormEntity(
            final AbstractMultipartForm multipart,
            final String contentType,
            final long contentLength) {
        super();
        this.multipart = multipart;
        this.contentType = new BasicHeader(HTTP.CONTENT_TYPE, contentType);
        this.contentLength = contentLength;
    }

    AbstractMultipartForm getMultipart() {
        return this.multipart;
    }

    public boolean isRepeatable() {
        return this.contentLength != -1;
    }

    public boolean isChunked() {
        return !isRepeatable();
    }

    public boolean isStreaming() {
        return !isRepeatable();
    }

    public long getContentLength() {
        return this.contentLength;
    }

    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 {
        throw new UnsupportedOperationException(
                    "Multipart form entity does not implement #getContent()");
    }

    public void writeTo(final OutputStream outstream) throws IOException {
        this.multipart.writeTo(outstream);
    }

}

通过查看源码可以发现，其实数据是保存在私有属性AbstractMultipartForm中的，并且有一个getMultipart()方法可以获取该属性，但是该方法只能同包下使用，所以新建一个相同路径的包，在该包下调用getMultipart()方法。代码如下

package org.apache.http.entity.mime;

import java.io.IOException;
import java.io.Reader;
import java.util.List;

import org.apache.http.HttpEntity;
import org.apache.http.entity.mime.content.StringBody;

public class MyHttpEntityUnil {

    public static void test( HttpEntity entity ) throws IOException{

        List<FormBodyPart> bodyParts = ((MultipartFormEntity)entity).getMultipart().getBodyParts();
        for( FormBodyPart bodyPart : bodyParts ){

            String name = bodyPart.getName();
            System.out.println(name);

            StringBody body = (StringBody) bodyPart.getBody();
            Reader reader = body.getReader();
            char[] cs = new char[1024];
            reader.read(cs);

            System.out.println(new String(cs));
        }
    }

}