Consumindo Web Services REST

Se você precisa consumir Web Services REST que utilizam JSON na requisição e na resposta, abaixo tem um exemplo de classe completa em Java que realiza GETs e POSTs em um determinado serviço. Também utilizei os métodos de transformação em JSON que mostrei em outro post.

import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.io.Reader;
import java.io.StringWriter;
import java.io.Writer;
import java.net.HttpURLConnection;
import java.net.URL;

import org.codehaus.jackson.JsonFactory;
import org.codehaus.jackson.JsonParser;
import org.codehaus.jackson.map.MappingJsonFactory;
import org.codehaus.jackson.map.ObjectMapper;

public class ClientWS {

   public static Object getObjeto(Class tipoObjetoRetorno, String urlWebService, String... parametros) {
      Object objetoRetorno = null;
	
      try {
         for(String parametro: parametros){
            urlWebService = urlWebService + "/" + parametro.replaceAll(" ", "%20");
         }
		
         URL url = new URL(urlWebService);
         HttpURLConnection connection = (HttpURLConnection) url.openConnection();
         connection.setRequestMethod("GET");
         connection.setConnectTimeout(15000);
         connection.setRequestProperty("login", "teste");
         connection.setRequestProperty("senha", "teste");
         connection.connect();

         String responseJson = inputStreamToString(connection.getInputStream());
         connection.disconnect();
		
         return fromJson(responseJson, tipoObjetoRetorno);

      } catch (Exception e) {
         e.printStackTrace();
      }	
      return objetoRetorno;
   }

   public static Object postObjeto(Object objetoEnvio, Class tipoObjetoRetorno, String urlWebService) {
      Object objetoRetorno = null;
	
      try {
         String requestJson = toJson(objetoEnvio);
		
         URL url = new URL(urlWebService);
         HttpURLConnection connection = (HttpURLConnection) url.openConnection();
         connection.setRequestMethod("POST");
         connection.setDoOutput(true);
         connection.setUseCaches(false);
	 connection.setConnectTimeout(15000);
         connection.setRequestProperty("login", "teste");
         connection.setRequestProperty("senha", "teste");
         connection.setRequestProperty("Content-Type", "application/json");
         connection.setRequestProperty("Accept", "application/json");
         connection.setRequestProperty("Content-Length", Integer.toString(requestJson.length()));
			
         DataOutputStream stream = new DataOutputStream(connection.getOutputStream());
         stream.write(requestJson.getBytes("UTF-8"));
         stream.flush();
         stream.close();
         connection.connect();

         String responseJson = inputStreamToString(connection.getInputStream());
         connection.disconnect();
         objetoRetorno = fromJson(responseJson, tipoObjetoRetorno);

      } catch (Exception e) {
         e.printStackTrace();
      }
      return objetoRetorno;
   }


   public static String inputStreamToString(InputStream is) throws IOException {
      if (is != null) {
         Writer writer = new StringWriter();

         char[] buffer = new char[1024];
         try {
            Reader reader = new BufferedReader(new InputStreamReader(is,"UTF-8"));
            int n;
            while ((n = reader.read(buffer)) != -1) {
               writer.write(buffer, 0, n);
            }
         } finally {
            is.close();
         }
         return writer.toString();
      } else {
         return "";
      }
   }

   public static String toJson(Object objeto) throws Exception {
      ObjectMapper mapper = new ObjectMapper();
      StringWriter jsonValue = new StringWriter();
      mapper.writeValue(new PrintWriter(jsonValue), objeto);
      return jsonValue.toString();
   }


   public static Object fromJson(String json, Class objectClass) throws Exception {
      JsonFactory f = new MappingJsonFactory();
      JsonParser jp = f.createJsonParser(json);
      Object obj = jp.readValueAs(objectClass);
      return obj;
   }

}