HTTPClient

参考
https://www.cnblogs.com/LuckyBao/p/6096145.html
丰富：
抽象类CloseableHttpClient为目前较实用的HttpClient接口抽象类
使用HttpClients.createDefault()实例化一个CloseableHttpClient类，实例的方式是使用HttpClientBuider.create().build()；
有意思的是

public static HttpClientBuilder create() {
        return new HttpClientBuilder();
    }
 public CloseableHttpClient build() {
 ...}
 这种模式

重要方法为execute，所有类型的execute方法都返回抽象方法doExecute来实现
doExecute(HttpHost target,HttpRequest request,HttpContext context)

@Override
    public CloseableHttpResponse execute(
            final HttpUriRequest request,
            final HttpContext context) throws IOException, ClientProtocolException {
        Args.notNull(request, "HTTP request");
        return doExecute(determineTarget(request), request, context);
    }

protected abstract CloseableHttpResponse doExecute(HttpHost target, HttpRequest request,
            HttpContext context) throws IOException, ClientProtocolException;

org.apache.http.client.methods.RequestBuilder使用这个builder创建各种HttpUriRequest