org.apache.http这个包是几年前的了，按照现在版本更迭的速度，估计过几年都没人能记起这个了吧。

先说问题

项目中类报红，提示找不到该类。

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpDelete;
import org.apache.http.client.methods.HttpEntityEnclosingRequestBase;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.methods.HttpPut;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.entity.ByteArrayEntity;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.params.HttpConnectionParams;
import org.apache.http.params.HttpParams;

错误: 程序包org.apache.http.impl.cookie不存在
import org.apache.http.impl.cookie.DateUtils;
 
错误: 程序包org.apache.http.client不存在
import org.apache.http.client.HttpClient;
 
错误: 程序包org.apache.http.client.methods不存在
import org.apache.http.client.methods.HttpDelete;
 
错误: 程序包org.apache.http.client.methods不存在
import org.apache.http.client.methods.HttpEntityEnclosingRequestBase;
 
错误: 程序包org.apache.http.client.methods不存在
import org.apache.http.client.methods.HttpGet;
 
错误: 程序包org.apache.http.client.methods不存在
import org.apache.http.client.methods.HttpPost;
 
错误: 程序包org.apache.http.client.methods不存在
import org.apache.http.client.methods.HttpPut;
 
错误: 程序包org.apache.http.client.methods不存在
import org.apache.http.client.methods.HttpUriRequest;
 
错误: 找不到符号
    protected final HttpClient mClient;
 
错误: 找不到符号
    public HttpClientStack(HttpClient client) {
                           ^
  符号:   类 HttpClient
  位置: 类 HttpClientStack
错误: 找不到符号
    private static void addHeaders(HttpUriRequest httpRequest, Map<String, String> headers) {
                                   ^
  符号:   类 HttpUriRequest
  位置: 类 HttpClientStack

解决方法：

在项目build.gradle中
在buildToolsVersion下边
defaultConfig上边

添加如下代码 

useLibrary 'org.apache.http.legacy'