java使用httpclient時，獲取HttpPost對象中的入參

 在某些特殊狀況下，須要獲取HttpPost對象中的參數，demo以下

public static HttpResponse test( HttpPost post ) throws IOException{
        
        /**
         * 入參是HttpPost，在該方法中想根據HttpPost中的參數作一些邏輯，這時候就須要想辦法獲取到HttpPost中的入參
         */
        HttpEntity entity = post.getEntity();      //代碼一
        
//      InputStream inputStream = entity.getContent();      //方法一
//      System.out.println(EntityUtils.toString(entity));   //方法二
        //獲取入參的方法
        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);
        
    }

常規思路如demo中的方法1、方法二都是經過獲取HttpEntity的輸入流（InputStream），可是會拋一個異常，緣由是該處使用的HttpEntity是實現類MultipartFormEntity，而MultipartFormEntity並無實現接口HttpEntity的getContent()方法。這時候就要轉變思路，查看MultipartFormEntity的源碼，以下

/*
 * ====================================================================
 * 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/>.
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 */

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);
    }

}

經過查看源碼能夠發現，其實數據是保存在私有屬性AbstractMultipartForm中的，而且有一個getMultipart()方法能夠獲取該屬性，可是該方法只能同包下使用，因此新建一個相同路徑的包，在該包下調用getMultipart()方法。代碼以下

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));
        }
    }
    
}