如何构建Http Get请求拼接参数

参考：https://www.cnblogs.com/honeybee/p/7879705.html

HttpClient4.X发送Get请求的参数拼接

　　使用httpClient发送get请求时，请求参数可以以？key=val&key1=val1的拼接到url后面。
但是请求参数较多时，这种方法比较麻烦，也不太优雅；研究了一下发现HttpClient4.X本身
是支持处理参数的。

1. 使用 URIBuilder来构建请求URI

httpclient相关的jar包mvn依赖：

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpcore</artifactId>
    <version>4.4.3</version>
</dependency>
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.1</version>
</dependency>

import com.google.common.collect.Lists;
import org.apache.http.Consts;
import org.apache.http.HttpEntity;
import org.apache.http.HttpStatus;
import org.apache.http.NameValuePair;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.utils.URIBuilder;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;

    private HttpGet buildHttpGet(String url, Map<String, String> para)
            throws URISyntaxException {
        URIBuilder builder = new URIBuilder(url);
        Set<String> set = para.keySet();
        for(String key: set){
            builder.setParameter(key, para.get(key));
        }
        HttpGet request = new HttpGet(builder.build());
        RequestConfig requestConfig = RequestConfig.custom()
                .setSocketTimeout(6000)
                .setConnectTimeout(6000)
                .setConnectionRequestTimeout(6000).build();
        request.setConfig(requestConfig);
        System.out.println(request.getURI().toString());
        return request;
    }

2. 使用 NameValuePair 来拼接URI

List<NameValuePair> params = Lists.newArrayList();
params.add(new BasicNameValuePair("cityEname", "henan"));
String str = "";
//转换为键值对
str = EntityUtils.toString(new UrlEncodedFormEntity(params, Consts.UTF_8));
System.out.println(str);
HttpGet httpGet = new HttpGet(url + "?" + str);

3. 根据 HttpGet反向获取键值对列表

HttpGet request = new HttpGet("http://example.com/?var=1&var=2");
URIBuilder newBuilder = new URIBuilder(request.getURI());
//获取键值对列表
List<NameValuePair> params = newBuilder.getQueryParams();
//转换为键值对字符串
String str = EntityUtils.toString(new UrlEncodedFormEntity(params, Consts.UTF_8));