[CALCITE-2027] Drop support for Java 7

.travis.yml

@@ -38,6 +38,6 @@ cache:
 matrix:
   fast_finish: true
   include:
-    - jdk: openjdk7
     - jdk: oraclejdk8
+    - jdk: oraclejdk9
 # End .travis.yml

mongodb/src/main/java/org/apache/calcite/adapter/mongodb/MongoEnumerator.java

@@ -120,7 +120,7 @@ static Function1<Document, Object> getter(
         ? (Function1) mapGetter()
         : fields.size() == 1
             ? singletonGetter(fields.get(0).getKey(), fields.get(0).getValue())
-            : listGetter(fields);
+            : (Function1) listGetter(fields);
   }
 
   private static Object convert(Object o, Class clazz) {

pom.xml

@@ -599,8 +599,8 @@ limitations under the License.
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-compiler-plugin</artifactId>
         <configuration>
-          <source>1.7</source>
-          <target>1.7</target>
+          <source>1.8</source>
+          <target>1.8</target>
           <compilerArgument>-Xlint:deprecation</compilerArgument>
         </configuration>
       </plugin>

site/_docs/howto.md

@@ -32,7 +32,7 @@ adapters.
 ## Building from a source distribution
 
 Prerequisites are maven (3.5.2 or later)
-and Java (JDK 7, 8, 9 or 10) on your path.
+and Java (JDK 8, 9 or 10) on your path.
 
 Unpack the source distribution `.tar.gz` or `.zip` file,
 `cd` to the root directory of the unpacked source,
@@ -50,7 +50,7 @@ tests.
 ## Building from git
 
 Prerequisites are git, maven (3.5.2 or later)
-and Java (JDK 7 or later, 9 preferred) on your path.
+and Java (JDK 8 or later, 9 preferred) on your path.
 
 Create a local copy of the github repository,
 `cd` to its root directory,
@@ -429,7 +429,7 @@ When the dry-run has succeeded, change `install` to `deploy`.
 Before you start:
 
 * Set up signing keys as described above.
-* Make sure you are using JDK 8 (not 7 or 9).
+* Make sure you are using JDK 8 (not 7, 9 or 10).
 * Check that `README` and `site/_docs/howto.md` have the correct version number.
 * Check that `NOTICE` has the current copyright year.
 * Set `version.major` and `version.minor` in `pom.xml`.

site/develop/index.md

@@ -41,7 +41,7 @@ user-friendly.
 ## Download source, build, and run tests
 
 Prerequisites are git, maven (3.5.2 or later)
-and Java (JDK 7 or later, 9 preferred) on your path.
+and Java (JDK 8 or later, 9 preferred) on your path.
 
 Create a local copy of the git repository, `cd` to its root directory,
 then build using maven: