Added getFirstMappedPort method (#377)

* Added no-args `getMappedPort` overloaded method (will use first exposed port)

CHANGELOG.md

@@ -6,6 +6,7 @@ All notable changes to this project will be documented in this file.
 
 ### Changed
 - Added support for Docker networks (#372)
+- Added `getFirstMappedPort` method
 
 ## [1.3.1] - 2017-06-22
 ### Fixed

core/src/main/java/org/testcontainers/containers/Container.java

@@ -304,6 +304,20 @@ default SELF withClasspathResourceMapping(final String resourcePath, final Strin
      */
     Boolean isRunning();
 
+    /**
+     * Get the actual mapped port for a first port exposed by the container.
+     *
+     * @return the port that the exposed port is mapped to
+     * @throws IllegalStateException if there are no exposed ports
+     */
+    default Integer getFirstMappedPort() {
+        return getExposedPorts()
+                .stream()
+                .findFirst()
+                .map(this::getMappedPort)
+                .orElseThrow(() -> new IllegalStateException("Container doesn't expose any ports"));
+    }
+
     /**
      * Get the actual mapped port for a given port exposed by the container.
      *

core/src/test/java/org/testcontainers/junit/GenericContainerRuleTest.java

@@ -325,7 +325,7 @@ private BufferedReader getReaderForContainerPort80(GenericContainer container) {
         return Unreliables.retryUntilSuccess(10, TimeUnit.SECONDS, () -> {
             Uninterruptibles.sleepUninterruptibly(1, TimeUnit.SECONDS);
 
-            Socket socket = new Socket(container.getContainerIpAddress(), container.getMappedPort(80));
+            Socket socket = new Socket(container.getContainerIpAddress(), container.getFirstMappedPort());
             return new BufferedReader(new InputStreamReader(socket.getInputStream()));
         });
     }