Classe util que busca o cep informado na API VIACEP, funciona bem no java 1.8

BuscaCepWSUtil.java

import java.io.IOException;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

import javax.json.Json;
import javax.json.JsonObject;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;

import com.fasterxml.jackson.annotation.JsonValue;


/**
 * https://github.com/uliss3s/ceputil Classe para recuperar informações do WS do
 * viacep.com.br
 */
public class BuscaCepWSUtil {

	private static final Set<String> CAMPOS = new HashSet<String>(
			Arrays.asList("cep", "logradouro", "complemento", "bairro", "localidade", "uf", "unidade", "ibge", "gia"));

	/**
	 * Recupera objeto Endereco pelo CEP
	 * 
	 * @param cep
	 *            String no formato 00000000
	 * @return instancia de br.com.viacep.Endereco
	 */
	public static Endereco getEnderecoPorCep(String cep) {

		JsonObject jsonObject = getCepResponse(cep);
		Endereco endereco = null;

		JsonValue erro = (JsonValue) jsonObject.get("erro");

		if (erro == null) {

			endereco = new Endereco();
			endereco.setCep(jsonObject.getString("cep"));
			endereco.setLogradouro(jsonObject.getString("logradouro"));
			endereco.setBairro(jsonObject.getString("bairro"));
			endereco.setMunicipio(jsonObject.getString("localidade"));
			endereco.setEstadoRecebendoEmString(jsonObject.getString("uf"));
		}

		return endereco;
	}

	/**
	 * Recupera Map<String,String> pelo CEP
	 * 
	 * @param cep
	 *            String no formato 00000000
	 * @return instancia de Map<String,String>
	 */
	public static Map<String, String> getMapPorCep(String cep) {

		JsonObject jsonObject = getCepResponse(cep);

		JsonValue erro = (JsonValue) jsonObject.get("erro");

		Map<String, String> mapa = null;
		if (erro == null) {
			mapa = new HashMap<String, String>();

			for (Iterator<Entry<String, javax.json.JsonValue>> it = jsonObject.entrySet().iterator(); it.hasNext();) {
				Entry<String, javax.json.JsonValue> entry = it.next();
				mapa.put(entry.getKey(), entry.getValue().toString());
			}
		}

		return mapa;
	}

	/**
	 * Método recebe o cep e faz a requisição no web service
	 * 
	 * @param cep
	 * @return retorna o response do web service
	 */
	private static JsonObject getCepResponse(String cep) {

		JsonObject responseJO = null;
		try {
			CloseableHttpClient httpclient = HttpClientBuilder.create().build();
			HttpGet httpGet = new HttpGet("https://viacep.com.br/ws/" + cep + "/json");
			HttpResponse response;

			response = httpclient.execute(httpGet);
			HttpEntity entity = response.getEntity();
			responseJO = Json.createReader(entity.getContent()).readObject();
		} catch (IOException e) {
			e.printStackTrace();
		}

		return responseJO;
	}

	public static Set<String> getCampos() {
		return CAMPOS;
	}
}