httpClient用Entity来封装报文实体。那么我们肯定可以从entity中获取请求体/响应体的数据。但是entity似乎并没有提供可以直接获取请求/响应体的方法。那么我们如何拿数据呢？

方法一：使用httpclient提供的工具类

response获取contentType response获取响应数据_java

EntityUtils类提供了一系列操作entity的方法，其中的toString方法就可以将entity中的响应数据输出位字符串

HttpEntity entity = response.getEntity();
//实体内容
String responseJson = EntityUtils.toString(entity, "UTF-8");

方法二：通过流

既然方法一可行，我们可以去看看方法一是怎么做的，看是否可以找到一种新的方式。下面对EntityUtils类中的toString()方法做一些简化。可以看到，先是通过entity获取了一个流。后面的就是操作流，然后对流中的数据编码，得到的就是实体内容。由此不难想到，实体内容很有可能是以流的形式存在的。想要弄清楚这个问题，我们首先要明白HttpEntity的工作方式

private static String toString(
    HttpEntity entity,
    ContentType contentType) throws IOException {
//获取一个含有实体信息的流
    InputStream inStream = entity.getContent();
    if (inStream == null) {
       return null;
    }
//这是从报文中获取的实体长度
    int capacity = (int)entity.getContentLength();
    if (capacity < 0) {
        capacity = DEFAULT_BUFFER_SIZE;
    }
//编码
    if (charset == null) {
        charset = HTTP.DEF_CONTENT_CHARSET;
    }
//从流中读取数据
    Reader reader = new InputStreamReader(inStream, charset);
    CharArrayBuffer buffer = new CharArrayBuffer(capacity);
    char[] tmp = new char[1024];
    int l;
    while((l = reader.read(tmp)) != -1) {
        buffer.append(tmp, 0, l);
    }
    return buffer.toString();
}
An entity that can be sent or received with an HTTP message. Entities can be found in 
some requests and in responses, where they are optional.
可以通过 HTTP 消息发送或接收的实体。实体可以在一些请求和响应中找到，它们是可选的。

There are three distinct types of entities in HttpCore, depending on where their content
 originates:
HttpCore 中有三种不同类型的实体，具体取决于它们的内容来源：

1.streamed: The content is received from a stream, or generated on the fly. Inparticular, 
this category includes entities being received from a connection. Streamed entities are 
generally not repeatable.
流式传输：内容是从流中接收的，或动态生成的。特别是，此类别包括从连接接收的实体。流式实体通常是不可重复的。

2.self-contained: The content is in memory or obtained by means that are independent from 
a connection or other entity. Self-contained entities are generally repeatable.
自包含：内容在内存中或通过独立于连接或其他实体的方式获得。自包含实体通常是可重复的。

3.wrapping: The content is obtained from another entity.
wrapping：内容是从另一个实体获取的。

This distinction is important for connection management with incoming entities. For 
entities that are created by an application and only sent using the HTTP components 
framework, the difference between streamed and self-contained is of little importance. In 
that case, it is suggested to consider non-repeatable entities as streamed, and those 
that are repeatable (without a huge effort) as self-contained.
这种区别对于与传入实体的连接管理很重要。对于由应用程序创建并且仅使用 HTTP 组件框架发送的实体，流式传输和自包含之间的区别并不重要。在这种情况下，建议将不可重复的实体视为流式传输，而将可重复（无需付出巨大努力）的实体视为独立的。

从api文档上可以了解到，HttpEntity数据来源主要是通过流的。我们可以通过HttpEntity中的getContent()方法来获取这个流，进而可以拿到实体数据