Retrofit的所有接口添加一个签名字段(值为原有键值对的MD

难点：获取已有的键值对
目标：获取已有的键值对，组成字符串加密后，新增一个字段signature，值为加密后的字符串。

import android.support.annotation.NonNull;
import android.support.v4.util.ArrayMap;

import com.linkfun.mpos.util.SignUtil;

import java.io.IOException;
import java.util.List;
import java.util.Set;

import okhttp3.HttpUrl;
import okhttp3.Interceptor;
import okhttp3.Request;
import okhttp3.Response;

/**
 * 对已有的接口多添加一个签名字段
 *
 * @author jdallen
 * @since 2019/4/2
 */

public class AddParameterInterceptor implements Interceptor {

    @Override
    public Response intercept(@NonNull Chain chain) throws IOException {
        Request oldRequest = chain.request();
        HttpUrl oldHttpUrl = oldRequest.url();
        //构建签名字段的值
        ArrayMap<String, String> signParams = new ArrayMap<>();
        //todo 现仅支持Get方法
        if (oldRequest.method().equals("GET")) {
            Set<String> nameList = oldHttpUrl.queryParameterNames();//获取所有的键
            for (String name : nameList) {
                List<String> valueList = oldHttpUrl.queryParameterValues(name);//获取指定键名的值
                if (null != valueList && valueList.size() > 0) {
                    signParams.put(name, valueList.get(0));
                } else {
                    signParams.put(name, null);
                }
            }
        }
        String signature = SignUtil.signMap(signParams);
        //新增签名字段
        HttpUrl url = oldHttpUrl.newBuilder()
                .addQueryParameter("signature", signature)
                .build();
        // Request customization: add request headers
        Request.Builder requestBuilder = oldRequest.newBuilder().url(url);
        return chain.proceed(requestBuilder.build());
    }
}