https://github.com/atomikos/transactions-essentials/issues/213

public/transactions-api/src/main/java/com/atomikos/icatch/provider/ConfigProperties.java

@@ -38,7 +38,8 @@ public final class ConfigProperties {
     public static final String LOG_LOCK_ACQUISITION_MAX_ATTEMPTS = "com.atomikos.icatch.log_lock_acquisition_max_attempts";
     public static final String LOG_LOCK_ACQUISITION_RETRY_DELAY = "com.atomikos.icatch.log_lock_acquisition_retry_delay";
 
-
+    public static final String REST_CLIENT_BUILDER = "com.atomikos.remoting.rest_client_builder";
+
 	/**
 	 * Replace ${...} sequence with the referenced value from the given properties or 
 	 * (if not found) the system properties -
@@ -272,6 +273,11 @@ public String getJvmId() {
         return getProperty(JVM_ID_PROPERTY_NAME);
 
     }
+
+    public String getRestClientBuilder() {
+        return getProperty(REST_CLIENT_BUILDER);
+
+    }
 
 
 }

public/transactions-remoting/src/main/java/com/atomikos/remoting/twopc/AtomikosRestPort.java

@@ -17,6 +17,7 @@
 import javax.ws.rs.PUT;
 import javax.ws.rs.Path;
 import javax.ws.rs.PathParam;
+import javax.ws.rs.Produces;
 import javax.ws.rs.WebApplicationException;
 import javax.ws.rs.core.MediaType;
 import javax.ws.rs.core.Response;
@@ -46,6 +47,7 @@
 
 @Path("/atomikos")
 @Consumes(HeaderNames.MimeType.APPLICATION_VND_ATOMIKOS_JSON)
+@Produces("text/plain")
 public class AtomikosRestPort {
 
 	public static final String REST_URL_PROPERTY_NAME = "com.atomikos.icatch.rest_port_url";

public/transactions-remoting/src/main/java/com/atomikos/remoting/twopc/DefaultRestClientBuilder.java

@@ -0,0 +1,18 @@
+package com.atomikos.remoting.twopc;
+
+import static javax.ws.rs.client.ClientBuilder.newClient;
+
+import javax.ws.rs.client.Client;
+
+/**
+ * Default provider for standard Jaxrs Client without connection pool
+ */
+public class DefaultRestClientBuilder extends RestClientBuilder {
+
+	public Client build() {
+		Client client = newClient();
+		client.property("jersey.config.client.suppressHttpComplianceValidation", true);
+		client.register(ParticipantsProvider.class);
+		return client;	
+	}
+}

public/transactions-remoting/src/main/java/com/atomikos/remoting/twopc/ParticipantAdapter.java

@@ -29,6 +29,7 @@
 import com.atomikos.icatch.Participant;
 import com.atomikos.icatch.RollbackException;
 import com.atomikos.icatch.SysException;
+import com.atomikos.icatch.config.Configuration;
 import com.atomikos.logging.Logger;
 import com.atomikos.logging.LoggerFactory;
 import com.atomikos.remoting.support.HeaderNames;
@@ -42,20 +43,29 @@ public class ParticipantAdapter implements Participant {
 
 	private static final Logger LOGGER = LoggerFactory.createLogger(ParticipantAdapter.class);
 
-	private final WebTarget target;
+	private static Client client;
+
+	private final URI uri; 
 
 	private final Map<String, Integer> cascadeList = new HashMap<>();
 
 	public ParticipantAdapter(URI uri) {
-		Client client = newClient();
-		client.property("jersey.config.client.suppressHttpComplianceValidation", true);
-		client.register(ParticipantsProvider.class);
-		target = client.target(uri);
+		if (client == null) {
+			String className = Configuration.getConfigProperties().getRestClientBuilder();
+			try {
+				Class<?> builderClass = Thread.currentThread().getContextClassLoader().loadClass(className);
+				RestClientBuilder restClientBuilder = (RestClientBuilder)builderClass.newInstance();
+				client = restClientBuilder.build();
+			} catch (Exception e) {
+				throw new IllegalArgumentException(e);
+			}
+		}
+		this.uri = uri;
 	}
 
 	@Override
 	public String getURI() {
-		return target.getUri().toASCIIString();
+		return uri.toASCIIString();
 	}
 
 	@Override
@@ -74,7 +84,7 @@ public int prepare() throws RollbackException, HeurHazardException, HeurMixedExc
 			LOGGER.logDebug("Calling prepare on " + getURI());
 		}
 		try {
-			int result = target.request()
+			int result = client.target(uri).request()
 					.buildPost(Entity.entity(cascadeList, HeaderNames.MimeType.APPLICATION_VND_ATOMIKOS_JSON))
 					.invoke(Integer.class);
 			if (LOGGER.isTraceEnabled()) {
@@ -84,9 +94,16 @@ public int prepare() throws RollbackException, HeurHazardException, HeurMixedExc
 		} catch (WebApplicationException e) {
 			int status = e.getResponse().getStatus();
 			if (status == 404) {
+				// 404 writes a String entity - we have to consume it
+				consumeStringEntity(e.getResponse());
 				LOGGER.logWarning("Remote participant not available - any remote work will rollback...", e);
 				throw new RollbackException();
 			} else {
+				if (status == 409) {
+					// 409 writes a String entity - we have to consume it
+					consumeStringEntity(e.getResponse());
+					e.getResponse().close();
+				}
 				LOGGER.logWarning("Unexpected error during prepare - see stacktrace for more details...", e);
 				throw new HeurHazardException();
 			}
@@ -100,17 +117,21 @@ public void commit(boolean onePhase)
 			LOGGER.logDebug("Calling commit on " + getURI());
 		}
 
-		Response r = target.path(String.valueOf(onePhase)).request().buildPut(Entity.entity("", HeaderNames.MimeType.APPLICATION_VND_ATOMIKOS_JSON)).invoke();
+		Response r = client.target(uri).path(String.valueOf(onePhase)).request().buildPut(Entity.entity("", HeaderNames.MimeType.APPLICATION_VND_ATOMIKOS_JSON)).invoke();
 
 		if (r.getStatusInfo().getFamily() != Family.SUCCESSFUL) {
 			int status = r.getStatus();
 			switch (status) {
 			case 404:
+				// 404 writes a String entity - we have to consume it
+				consumeStringEntity(r);
 				if (onePhase) {
 					LOGGER.logWarning("Remote participant not available - default outcome will be rollback");
 					throw new RollbackException();
 				}
 			case 409:
+				// 409 writes a String entity - we have to consume it
+				consumeStringEntity(r);
 				LOGGER.logWarning("Unexpected 409 error on commit");
 				throw new HeurMixedException();
 			default:
@@ -127,12 +148,14 @@ public void rollback() throws HeurCommitException, HeurMixedException, HeurHazar
 			LOGGER.logDebug("Calling rollback on " + getURI());
 		}
 
-		Response r = target.request().header(HttpHeaders.CONTENT_TYPE, HeaderNames.MimeType.APPLICATION_VND_ATOMIKOS_JSON).delete();
+		Response r = client.target(uri).request().header(HttpHeaders.CONTENT_TYPE, HeaderNames.MimeType.APPLICATION_VND_ATOMIKOS_JSON).delete();
 
 		if (r.getStatusInfo().getFamily() != Family.SUCCESSFUL) {
 			int status = r.getStatus();
 			switch (status) {
 			case 409:
+				// 409 writes a String entity - we have to consume it
+				consumeStringEntity(r);
 				LOGGER.logWarning("Unexpected 409 error on rollback");
 				throw new HeurMixedException();
 			case 404:
@@ -174,5 +197,15 @@ public int hashCode() {
 	public String toString() {
 		return "ParticipantAdapter for: " + getURI();
 	}
+
+	private void consumeStringEntity(Response r) {
+		// the entity body has to be consumed to allow pooling of http connections.
+		// see https://stackoverflow.com/questions/27063667/httpclient-4-3-blocking-on-connection-pool
+		try {
+			r.readEntity(String.class);
+		} catch (Exception e) {
+			// catch exception. we only want to be sure that all content was cosumed
+		}
+	}
 
 }

public/transactions-remoting/src/main/java/com/atomikos/remoting/twopc/RestClientBuilder.java

@@ -0,0 +1,53 @@
+package com.atomikos.remoting.twopc;
+
+import javax.ws.rs.client.Client;
+
+/**
+ * Abstract Builder for creation of Rest Client
+ * 
+ * You can create a sublcass if you need some special handling like connection polling, timeouts, ...
+ * Implementation is defined by the property com.atomikos.remoting.rest_client_builder
+ * Default in transaction-default.properties is
+ * com.atomikos.remoting.rest_client_builder=com.atomikos.remoting.twopc.DefaultRestClientBuilder
+ * 
+ * Here some example:
+ * <pre>
+ * 
+ * public class PooledRestClientBuilder extends RestClientBuilder {
+
+	@Override
+	public Client build() {
+		ResteasyClientBuilder builder = new ResteasyClientBuilder();
+
+		ConfigProperties configProperties = Configuration.getConfigProperties();
+		String connectionPoolSizeProperty = configProperties.getProperty("com.atomikos.remoting.twopc.ParticipantAdapter.connectionPoolSize");
+		int connectionPoolSize = 20;
+		if (connectionPoolSizeProperty != null)
+			connectionPoolSize = Integer.valueOf(connectionPoolSizeProperty);
+
+		String connectTimeoutProperty = configProperties.getProperty("com.atomikos.remoting.twopc.ParticipantAdapter.connectTimeout");
+		int connectTimeout = 10;
+		if (connectTimeoutProperty != null)
+			connectTimeout = Integer.valueOf(connectTimeoutProperty);
+
+		String readTimeoutProperty = configProperties.getProperty("com.atomikos.remoting.twopc.ParticipantAdapter.readTimeout");
+		int readTimeout = 60;
+		if (readTimeoutProperty != null)
+			readTimeout = Integer.valueOf(readTimeoutProperty);
+
+		builder.connectTimeout(connectTimeout, TimeUnit.SECONDS);
+		builder.readTimeout(readTimeout, TimeUnit.SECONDS);
+		Client c = builder.connectionPoolSize(connectionPoolSize).build(); 
+		c.property("jersey.config.client.suppressHttpComplianceValidation", true);
+		c.register(ParticipantsProvider.class);
+		return c;
+	}
+}
+ * 
+ * </pre>
+ */
+public abstract class RestClientBuilder {
+
+	public abstract Client build();
+
+}

public/transactions/src/main/resources/transactions-defaults.properties

@@ -24,3 +24,4 @@ com.atomikos.icatch.logcloud_datasource_name=logCloudDS
 com.atomikos.icatch.throw_on_heuristic=false
 com.atomikos.icatch.log_lock_acquisition_max_attempts=3
 com.atomikos.icatch.log_lock_acquisition_retry_delay=1000
+com.atomikos.remoting.rest_client_builder=com.atomikos.remoting.twopc.DefaultRestClientBuilder