Fix Java 8 API compatibility

Author: games647

bukkit/src/main/java/com/github/games647/fastlogin/bukkit/PremiumPlaceholder.java

@@ -25,6 +25,7 @@
  */
 package com.github.games647.fastlogin.bukkit;
 
+import java.util.Collections;
 import java.util.List;
 
 import me.clip.placeholderapi.expansion.PlaceholderExpansion;
@@ -49,7 +50,7 @@ public boolean persist() {
 
     @Override
     public @NotNull List<String> getPlaceholders() {
-        return List.of(PLACEHOLDER_VARIABLE);
+        return Collections.singletonList(PLACEHOLDER_VARIABLE);
     }
 
     @Override

bukkit/src/main/java/com/github/games647/fastlogin/bukkit/command/ToggleCommand.java

@@ -81,7 +81,7 @@ protected void sendBungeeActivateMessage(CommandSender invoker, String target, b
             plugin.getBungeeManager().sendPluginMessage((PluginMessageRecipient) invoker, message);
         } else {
             Optional<? extends Player> optPlayer = Bukkit.getServer().getOnlinePlayers().stream().findFirst();
-            if (optPlayer.isEmpty()) {
+            if (!optPlayer.isPresent()) {
                 plugin.getLog().info("No player online to send a plugin message to the proxy");
                 return;
             }

core/src/main/java/com/github/games647/fastlogin/core/hooks/DefaultPasswordGenerator.java

@@ -26,7 +26,7 @@
 package com.github.games647.fastlogin.core.hooks;
 
 import java.security.SecureRandom;
-import java.util.random.RandomGenerator;
+import java.util.Random;
 import java.util.stream.IntStream;
 
 public class DefaultPasswordGenerator<P> implements PasswordGenerator<P> {
@@ -35,7 +35,7 @@ public class DefaultPasswordGenerator<P> implements PasswordGenerator<P> {
     private static final char[] PASSWORD_CHARACTERS = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
             .toCharArray();
 
-    private final RandomGenerator random = new SecureRandom();
+    private final Random random = new SecureRandom();
 
     @Override
     public String getRandomPassword(P player) {

core/src/main/java/com/github/games647/fastlogin/core/shared/JoinManagement.java

@@ -93,7 +93,7 @@ public void onLogin(String username, S source) {
                     premiumUUID = core.getResolver().findProfile(username);
                 }
 
-                if (premiumUUID.isEmpty()
+                if (!premiumUUID.isPresent()
                         || (!checkNameChange(source, username, premiumUUID.get())
                         && !checkPremiumName(source, username, profile))) {
                     //nothing detected the player as premium -> start a cracked session

pom.xml

@@ -49,8 +49,6 @@
         <git.commit.id>Unknown</git.commit.id>
 
         <java.version>8</java.version>
-        <maven.compiler.source>${java.version}</maven.compiler.source>
-        <maven.compiler.target>${java.version}</maven.compiler.target>
 
         <floodgate.version>2.2.0-SNAPSHOT</floodgate.version>
         <geyser.version>2.0.0-SNAPSHOT</geyser.version>
@@ -152,6 +150,8 @@
                     </execution>
                 </executions>
             </plugin>
+
+            <!-- Require newer versions for Junit5 support -->
             <plugin>
                 <artifactId>maven-surefire-plugin</artifactId>
                 <version>2.22.2</version>
@@ -160,6 +160,19 @@
                 <artifactId>maven-failsafe-plugin</artifactId>
                 <version>2.22.2</version>
             </plugin>
+
+            <!-- Verify Java 8 compatibility while compiling with a newer toolchain 
+            (i.e. check for unavailable methods) -->
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.10.1</version>
+                <configuration>
+                    <source>${java.version}</source>
+                    <target>${java.version}</target>
+                    <release>${java.version}</release>
+                </configuration>
+            </plugin>
         </plugins>
 
         <resources>