Set Java 11 as source+target version

As Hono has problems building on Java 8, and we already ship Java 11
images, we decided to fully switch to Java 11. But keeping the
classpath model.

This PR switches to Java 11 for source+target, and also makes use
of a few Java 11-only features, just test it.

Author: ctron

.travis.yml

@@ -3,7 +3,6 @@ sudo: required
 language: java
 
 jdk:
-#  - openjdk8
   - openjdk11
 
 script:

adapters/coap-vertx/src/main/java/org/eclipse/hono/adapter/coap/vertx/VertxBasedCoapAdapter.java

@@ -58,7 +58,7 @@ protected String getTypeName() {
     public void getExtendedDevice(final CoapExchange exchange, final Handler<ExtendedDevice> handler) {
         try {
             final List<String> pathList = exchange.getRequestOptions().getUriPath();
-            final String[] path = pathList.toArray(new String[pathList.size()]);
+            final String[] path = pathList.toArray(String[]::new);
             final ResourceIdentifier identifier = ResourceIdentifier.fromPath(path);
             final Device device = new Device(identifier.getTenantId(), identifier.getResourceId());
             final Principal peer = exchange.advanced().getRequest().getSourceContext().getPeerIdentity();
@@ -69,9 +69,9 @@ public void getExtendedDevice(final CoapExchange exchange, final Handler<Extende
             } else {
                 getAuthenticatedExtendedDevice(device, exchange, handler);
             }
-        } catch (NullPointerException cause) {
+        } catch (final NullPointerException cause) {
             CoapErrorResponse.respond(exchange, "missing tenant and device!", ResponseCode.BAD_REQUEST);
-        } catch (Throwable cause) {
+        } catch (final Throwable cause) {
             CoapErrorResponse.respond(exchange, cause, ResponseCode.INTERNAL_SERVER_ERROR);
         }
     }

core/src/main/java/org/eclipse/hono/util/AuthenticationConstants.java

@@ -162,7 +162,7 @@ public static String[] parseSaslResponse(final byte[] saslResponse) throws Crede
         } else if (fields.get(2) == null || fields.get(2).length() == 0) {
             throw new CredentialException("PLAIN response must contain a password");
         } else {
-            return fields.toArray(new String[3]);
+            return fields.toArray(String[]::new);
         }
     }
 }

core/src/main/java/org/eclipse/hono/util/Hostnames.java

@@ -24,13 +24,13 @@ public final class Hostnames {
     static {
 
         // works on Linux
-        String hostname = System.getenv("HOSTNAME");
+        var hostname = System.getenv("HOSTNAME");
 
         if (hostname == null) {
             // this can produce all kinds of unexpected results
             // but better than nothing
             try {
-                final InetAddress localhost = InetAddress.getLocalHost();
+                final var localhost = InetAddress.getLocalHost();
                 hostname = localhost.getHostAddress();
             } catch (final Exception e) {
             }

core/src/main/java/org/eclipse/hono/util/ResourceIdentifier.java

@@ -60,7 +60,7 @@ private ResourceIdentifier(final String resource, final boolean assumeDefaultTen
         if (assumeDefaultTenant) {
             pathSegments.add(1, Constants.DEFAULT_TENANT);
         }
-        setResourcePath(pathSegments.toArray(new String[pathSegments.size()]));
+        setResourcePath(pathSegments.toArray(String[]::new));
     }
 
     private ResourceIdentifier(final String endpoint, final String tenantId, final String resourceId) {
@@ -94,7 +94,7 @@ private void setResourcePath(final String[] path) {
                 pathSegments.add(segment);
             }
         }
-        this.resourcePath = pathSegments.toArray(new String[pathSegments.size()]);
+        this.resourcePath = pathSegments.toArray(String[]::new);
         if (resourcePath.length > IDX_TENANT_ID && resourcePath[IDX_TENANT_ID].length() == 0) {
             resourcePath[IDX_TENANT_ID] = null;
         }

pom.xml

@@ -236,10 +236,10 @@
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-compiler-plugin</artifactId>
-          <version>3.7.0</version>
+          <version>3.8.0</version>
           <configuration>
-            <source>1.8</source>
-            <target>1.8</target>
+            <source>11</source>
+            <target>11</target>
             <encoding>UTF-8</encoding>
           </configuration>
         </plugin>

services/auth/src/main/java/org/eclipse/hono/service/auth/impl/FileBasedAuthenticationService.java

@@ -196,7 +196,7 @@ private Authorities toAuthorities(final JsonArray authorities) {
                           activityList.add(act);
                       }
                   });
-                  result.addResource(resource, activityList.toArray(new Activity[activityList.size()]));
+                        result.addResource(resource, activityList.toArray(Activity[]::new));
               } else if (operation != null) {
                   final String[] parts = operation.split(":", 2);
                   if (parts.length == 2) {

services/auth/src/main/java/org/eclipse/hono/service/auth/impl/SimpleAuthenticationServer.java

@@ -177,7 +177,7 @@ private int[] parseVersionString(final String version) {
             default:
                 // return 0.0.0
             }
-        } catch (NumberFormatException e) {
+        } catch (final NumberFormatException e) {
             // return 0.0.0
         }
         return result;
@@ -204,7 +204,7 @@ private String[] getAuthorities(final String activities) {
                 return null;
             }
         }).filter(Objects::nonNull).collect(Collectors.toSet());
-        return result.toArray(new String[result.size()]);
+        return result.toArray(String[]::new);
     }
 
     @Override