Build for Java 8 rather than Java 7. (#2744)

* Build for Java 8 rather than Java 7.

Part of #2743.

* Further adjustments to remove traces of Java 7.

README.md

@@ -43,7 +43,8 @@ Maven:
 
 ### Requirements
 #### Minimum Java version
-- Gson 2.9.0 and newer: Java 7
+- Gson 2.12.0 and newer: Java 8
+- Gson 2.9.0 to 2.11.0: Java 7
 - Gson 2.8.9 and older: Java 6
 
 Despite supporting older Java versions, Gson also provides a JPMS module descriptor (module name `com.google.gson`) for users of Java 9 or newer.

gson/src/test/java/com/google/gson/integration/OSGiManifestIT.java

@@ -144,8 +144,7 @@ public void testExports() {
 
   @Test
   public void testRequireCapability() {
-    // When building with JDK >= 21, the minimum target version is Java 8
-    String expectedJavaVersion = Runtime.version().feature() < 21 ? "1.7" : "1.8";
+    String expectedJavaVersion = "1.8";
 
     // Defines the minimum required Java version
     assertThat(getAttribute("Require-Capability"))

gson/src/test/java/com/google/gson/internal/JavaVersionTest.java

@@ -30,8 +30,8 @@ public class JavaVersionTest {
 
   @Test
   public void testGetMajorJavaVersion() {
-    // Gson currently requires at least Java 7
-    assertThat(JavaVersion.getMajorJavaVersion()).isAtLeast(7);
+    // Gson currently requires at least Java 8
+    assertThat(JavaVersion.getMajorJavaVersion()).isAtLeast(8);
   }
 
   @Test

pom.xml

@@ -38,7 +38,7 @@
 
   <properties>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-    <maven.compiler.release>7</maven.compiler.release>
+    <maven.compiler.release>8</maven.compiler.release>
     <maven.compiler.testRelease>11</maven.compiler.testRelease>
 
     <!-- Make the build reproducible, see https://maven.apache.org/guides/mini/guide-reproducible-builds.html -->
@@ -556,20 +556,6 @@
       </build>
     </profile>
 
-    <!-- Slightly adjust build to support building with JDK >= 21
-      However, by default this will intentionally be blocked by the Maven Enforcer Plugin defined above
-      and must be explicitly circumvented to avoid building non-release Gson artifacts by accident -->
-    <profile>
-      <id>jdk21+</id>
-      <activation>
-        <jdk>[21,)</jdk>
-      </activation>
-      <properties>
-        <!-- JDK 21 does not support Java 7 as release, must use at least Java 8 -->
-        <maven.compiler.release>8</maven.compiler.release>
-      </properties>
-    </profile>
-
     <!-- Profile defining additional plugins to be executed for release -->
     <profile>
       <id>release</id>