Support for JDK21 (#150)

Motivation:
JDK21 GA has been released

Modification:
Add JDK 21 environment

Result:
Ensures compatibility with JDK21

Author: jchrys

.github/workflows/ci-unit-tests.yml

@@ -9,14 +9,14 @@ jobs:
     runs-on: ubuntu-20.04
     strategy:
       matrix:
-        java-version: [ 8, 11, 17 ]
+        java-version: [ 8, 11, 17 , 21]
     name: linux-java-${{ matrix.java-version }}
     steps:
       - uses: actions/checkout@v3
       - name: Set up Java ${{ matrix.java-version }}
         uses: actions/setup-java@v3
         with:
-          distribution: temurin
+          distribution: zulu
           java-version: ${{ matrix.java-version }}
           cache: maven
       - name: Unit test with Maven

src/main/java/io/asyncer/r2dbc/mysql/codec/DefaultCodecs.java

@@ -26,6 +26,7 @@
 import io.r2dbc.spi.Parameter;
 import org.jetbrains.annotations.Nullable;
 
+import javax.annotation.concurrent.GuardedBy;
 import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
 import java.math.BigInteger;
@@ -314,26 +315,29 @@ private static Codec<?>[] defaultCodecs(ByteBufAllocator allocator) {
         };
     }
 
-    static final class Builder extends ArrayList<Codec<?>> implements CodecsBuilder {
+    static final class Builder implements CodecsBuilder {
 
         private final ByteBufAllocator allocator;
 
+        @GuardedBy("this")
+        private final ArrayList<Codec<?>> codecs = new ArrayList<>();
+
         Builder(ByteBufAllocator allocator) {
             this.allocator = allocator;
         }
 
         @Override
         public CodecsBuilder addFirst(Codec<?> codec) {
             synchronized (this) {
-                if (isEmpty()) {
-                    Codec<?>[] codecs = defaultCodecs(allocator);
+                if (codecs.isEmpty()) {
+                    Codec<?>[] defaultCodecs = defaultCodecs(allocator);
 
-                    ensureCapacity(codecs.length + 1);
+                    codecs.ensureCapacity(defaultCodecs.length + 1);
                     // Add first.
-                    add(codec);
-                    addAll(InternalArrays.asImmutableList(codecs));
+                    codecs.add(codec);
+                    codecs.addAll(InternalArrays.asImmutableList(defaultCodecs));
                 } else {
-                    add(0, codec);
+                    codecs.add(0, codec);
                 }
             }
             return this;
@@ -342,10 +346,10 @@ public CodecsBuilder addFirst(Codec<?> codec) {
         @Override
         public CodecsBuilder addLast(Codec<?> codec) {
             synchronized (this) {
-                if (isEmpty()) {
-                    addAll(InternalArrays.asImmutableList(defaultCodecs(allocator)));
+                if (codecs.isEmpty()) {
+                    codecs.addAll(InternalArrays.asImmutableList(defaultCodecs(allocator)));
                 }
-                add(codec);
+                codecs.add(codec);
             }
             return this;
         }
@@ -354,13 +358,13 @@ public CodecsBuilder addLast(Codec<?> codec) {
         public Codecs build() {
             synchronized (this) {
                 try {
-                    if (isEmpty()) {
+                    if (codecs.isEmpty()) {
                         return new DefaultCodecs(defaultCodecs(allocator));
                     }
-                    return new DefaultCodecs(toArray(new Codec<?>[0]));
+                    return new DefaultCodecs(codecs.toArray(new Codec<?>[0]));
                 } finally {
-                    clear();
-                    trimToSize();
+                    codecs.clear();
+                    codecs.trimToSize();
                 }
             }
         }