[FLINK-36181] Make sure that JDK11 APIs can be used

Author: MartijnVisser

pom.xml

@@ -124,6 +124,7 @@ under the License.
 		<flink.shaded.jackson.version>2.15.3</flink.shaded.jackson.version>
 		<flink.shaded.jsonpath.version>2.7.0</flink.shaded.jsonpath.version>
 		<flink.markBundledAsOptional>true</flink.markBundledAsOptional>
+		<source.java.version>11</source.java.version>
 		<target.java.version>17</target.java.version>
 		<slf4j.version>1.7.36</slf4j.version>
 		<log4j.version>2.24.1</log4j.version>
@@ -1120,7 +1121,8 @@ under the License.
 						<groupId>org.apache.maven.plugins</groupId>
 						<artifactId>maven-compiler-plugin</artifactId>
 						<configuration>
-							<source>17</source>
+							<!-- Make sure that we only use Java 11 compatible APIs -->
+							<source>11</source>
 							<target>17</target>
 							<compilerArgs combine.children="append">
 								<arg>--add-exports=java.base/sun.net.util=ALL-UNNAMED</arg>
@@ -2082,7 +2084,8 @@ under the License.
 					<artifactId>maven-compiler-plugin</artifactId>
 					<version>3.8.0</version>
 					<configuration>
-						<source>${target.java.version}</source>
+						<!-- Make sure that we only use Java 11 compatible APIs -->
+						<source>${source.java.version}</source>
 						<target>${target.java.version}</target>
 						<!-- The semantics of this option are reversed, see MCOMPILER-209. -->
 						<useIncrementalCompilation>false</useIncrementalCompilation>