Add a hasAdapter method to the JsonB interface

jsonb/src/main/java/io/avaje/jsonb/Jsonb.java

@@ -235,6 +235,8 @@ static Jsonb instance() {
    * When using <code>Object.class</code> and reading <code>fromJson()</code> then the java types used in
    * the result are determined dynamically based on the json types being read and the resulting java types
    * are ArrayList, LinkedHashMap, String, boolean, and double.
+   *
+   * @throws IllegalStateException if an adapter cannot be found
    */
   <T> JsonType<T> type(Class<T> cls);
 
@@ -279,6 +281,8 @@ static Jsonb instance() {
    * When using <code>Object.class</code> and reading <code>fromJson()</code> then the java types used in
    * the result are determined dynamically based on the json types being read and the resulting java types
    * are ArrayList, LinkedHashMap, String, boolean, and double.
+   *
+   * @throws IllegalStateException if an adapter cannot be found
    */
   <T> JsonType<T> type(Type type);
 
@@ -341,6 +345,8 @@ static Jsonb instance() {
    *
    * <p>JsonAdapter is generally used by generated serialization code. Application code should use
    * {@link Jsonb#type(Class)} and {@link JsonType} instead.
+   *
+   * @throws IllegalStateException if an adapter cannot be found
    */
   <T> JsonAdapter<T> adapter(Class<T> cls);
 
@@ -349,6 +355,8 @@ static Jsonb instance() {
    *
    * <p>JsonAdapter is generally used by generated serialization code. Application code should use
    * {@link Jsonb#type(Type)} and {@link JsonType} instead.
+   *
+   * @throws IllegalStateException if an adapter cannot be found
    */
   <T> JsonAdapter<T> adapter(Type type);
 
@@ -368,6 +376,22 @@ static Jsonb instance() {
    */
   JsonAdapter<String> rawAdapter();
 
+  /**
+   * Check if a JsonAdapter exists for the given class.
+   *
+   * @param cls The class to check for adapter availability
+   * @return true if an adapter exists, false otherwise
+   */
+  boolean hasAdapter(Class<?> cls);
+
+  /**
+   * Check if a JsonAdapter exists for the given type.
+   *
+   * @param type The type to check for adapter availability
+   * @return true if an adapter exists, false otherwise
+   */
+  boolean hasAdapter(Type type);
+
   /**
    * Build the Jsonb instance adding JsonAdapter, Factory or AdapterBuilder.
    */

jsonb/src/main/java/io/avaje/jsonb/core/CoreAdapterBuilder.java

@@ -61,17 +61,26 @@ <T> JsonAdapter<T> get(Object cacheKey) {
   }
 
   /**
-   * Build for the simple non-annotated type case.
+   * Check if an adapter exists or can be created for the given cache key.
+   * If an adapter can be created, it will be cached for subsequent use.
    */
-  <T> JsonAdapter<T> build(Type type) {
-    return build(type, type);
+  boolean hasAdapter(Type cacheKey) {
+    if (adapterCache.containsKey(cacheKey)) {
+      return true;
+    }
+    return lookupAdapter(cacheKey, cacheKey, false) != null;
   }
 
   /**
-   * Build given type and annotations.
+   * Try to create an adapter for the given type, with optional exception handling.
+   *
+   * @param type The type to create an adapter for
+   * @param cacheKey The cache key to use
+   * @return The created adapter, or null if no factory can create it and throwOnFailure is false
+   * @throws IllegalArgumentException if no adapter found and throwOnFailure is true
    */
   @SuppressWarnings("unchecked")
-  <T> JsonAdapter<T> build(Type type, Object cacheKey) {
+  private <T> JsonAdapter<T> lookupAdapter(Type type, Object cacheKey, boolean throwOnFailure) {
     LookupChain lookupChain = lookupChainThreadLocal.get();
     if (lookupChain == null) {
       lookupChain = new LookupChain();
@@ -94,19 +103,40 @@ <T> JsonAdapter<T> build(Type type, Object cacheKey) {
           return result;
         }
       }
-      throw new IllegalArgumentException(
+
+      if (throwOnFailure) {
+        throw new IllegalArgumentException(
           "No JsonAdapter for "
-              + type
-              + "\nPossible Causes: \n"
-              + "1. Missing @Json or @Json.Import annotation.\n"
-              + "2. The avaje-jsonb-generator dependency was not available during compilation\n");
+            + type
+            + "\nPossible Causes: \n"
+            + "1. Missing @Json or @Json.Import annotation.\n"
+            + "2. The avaje-jsonb-generator dependency was not available during compilation\n");
+      }
+      return null;  // No adapter found
     } catch (IllegalArgumentException e) {
-      throw lookupChain.exceptionWithLookupStack(e);
+      if (throwOnFailure) {
+        throw lookupChain.exceptionWithLookupStack(e);
+      }
+      return null;
     } finally {
       lookupChain.pop(success);
     }
   }
 
+  /**
+   * Build for the simple non-annotated type case.
+   */
+  <T> JsonAdapter<T> build(Type type) {
+    return build(type, type);
+  }
+
+  /**
+   * Build given type and annotations.
+   */
+  <T> JsonAdapter<T> build(Type type, Object cacheKey) {
+    return lookupAdapter(type, cacheKey, true);
+  }
+
   /**
    * A possibly-reentrant chain of lookups for JSON adapters.
    *

jsonb/src/main/java/io/avaje/jsonb/core/DJsonb.java

@@ -212,6 +212,18 @@ public JsonAdapter<String> rawAdapter() {
     return RawAdapter.STR;
   }
 
+  @Override
+  public boolean hasAdapter(Class<?> cls) {
+    Type cacheKey = canonicalizeClass(requireNonNull(cls));
+    return builder.hasAdapter(cacheKey);
+  }
+
+  @Override
+  public boolean hasAdapter(Type type) {
+    type = removeSubtypeWildcard(canonicalize(requireNonNull(type)));
+    return builder.hasAdapter(type);
+  }
+
   JsonReader objectReader(Object value) {
     return new ObjectJsonReader(value);
   }

jsonb/src/test/java/io/avaje/jsonb/core/HasAdapterTest.java

@@ -0,0 +1,71 @@
+package io.avaje.jsonb.core;
+
+import io.avaje.jsonb.Jsonb;
+import io.avaje.jsonb.Types;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import java.lang.reflect.Type;
+import java.util.Optional;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class HasAdapterTest {
+
+  private final Jsonb jsonb = Jsonb.builder().build();
+
+  @Test
+  @DisplayName("hasAdapter returns true for basic types and primitives")
+  void hasAdapter_basicTypes_returnsTrue() {
+    assertThat(jsonb.hasAdapter(String.class)).isTrue();
+    assertThat(jsonb.hasAdapter(Integer.class)).isTrue();
+    assertThat(jsonb.hasAdapter(Boolean.class)).isTrue();
+
+    assertThat(jsonb.hasAdapter(int.class)).isTrue();
+    assertThat(jsonb.hasAdapter(boolean.class)).isTrue();
+    assertThat(jsonb.hasAdapter(double.class)).isTrue();
+  }
+
+  @Test
+  @DisplayName("hasAdapter returns true for generic types like List, Map, and Optional")
+  void hasAdapter_withGenericTypes_returnsTrue() {
+    Type listOfString = Types.listOf(String.class);
+    assertThat(jsonb.hasAdapter(listOfString)).isTrue();
+
+    Type mapOfStringToInteger = Types.mapOf(Integer.class);
+    assertThat(jsonb.hasAdapter(mapOfStringToInteger)).isTrue();
+
+    Type optionalString = Types.newParameterizedType(Optional.class, String.class);
+    assertThat(jsonb.hasAdapter(optionalString)).isTrue();
+  }
+
+  @Test
+  @DisplayName("hasAdapter returns false for types without adapters")
+  void hasAdapter_whenAdapterNotExists_returnsFalse() {
+    assertThat(jsonb.hasAdapter(UnknownClass.class)).isFalse();
+    assertThat(jsonb.hasAdapter(SomeInterface.class)).isFalse();
+  }
+
+  @Test
+  @DisplayName("hasAdapter works correctly with cached adapters")
+  void hasAdapter_withCachedAdapter_returnsTrue() {
+    jsonb.type(String.class);
+    assertThat(jsonb.hasAdapter(String.class)).isTrue();
+  }
+
+  @Test
+  @DisplayName("hasAdapter never throws exceptions, even for problematic types")
+  void hasAdapter_doesNotThrowExceptions() {
+    assertThat(jsonb.hasAdapter(UnknownClass.class)).isFalse();
+    assertThat(jsonb.hasAdapter(SomeInterface.class)).isFalse();
+  }
+
+  // Test classes
+  private static class UnknownClass {
+    private String value;
+  }
+
+  private interface SomeInterface {
+    String getValue();
+  }
+}