Added StopWatch class and a generic type adapter that can exclude fields.

2025-04-09 10:19:05 +02:00
parent 547c582dbf
commit 78f78adea7
2 changed files with 264 additions and 0 deletions
@@ -0,0 +1,136 @@
+package de.neitzel.gson.adapter;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.JsonObject;
+import com.google.gson.TypeAdapter;
+import com.google.gson.internal.Streams;
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonWriter;
+
+import java.io.IOException;
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * A custom {@link TypeAdapter} implementation for selectively excluding specified fields during JSON serialization.
+ *
+ * This adapter facilitates both serialization and deserialization of objects while providing functionality to remove specified
+ * fields from the serialized output. The set of excluded field names is provided during the adapter's initialization.
+ *
+ * @param <T> the type of objects that this adapter can serialize and deserialize
+ */
+public class ExcludeFieldsAdapter<T> extends TypeAdapter<T> {
+
+  /**
+   * The type of objects that this adapter handles for serialization and deserialization.
+   *
+   * This is a generic class type parameter representing the class of objects that the
+   * {@link ExcludeFieldsAdapter} instance is designed to process. It ensures type
+   * safety and guarantees the compatibility of the adapter with a specific object type.
+   */
+  private final Class<T> type;
+  /**
+   * A set containing the names of fields to be excluded during JSON serialization.
+   *
+   * This collection is used in the {@link ExcludeFieldsAdapter} to determine which fields should be removed from the
+   * serialized JSON representation of an object. The fields to be excluded are specified during the initialization
+   * of the adapter.
+   */
+  private final Set<String> excludedFields;
+
+  /**
+   * An instance of the Gson library used for JSON serialization and deserialization.
+   *
+   * This variable holds the Gson object that is utilized to handle the conversion processes within the
+   * custom serialization and deserialization logic. If not explicitly provided during initialization,
+   * it can be lazily initialized using a GsonBuilder.
+   */
+  private Gson gson;
+
+  /**
+   * A {@link GsonBuilder} instance used for configuring and creating {@link Gson} objects within the adapter.
+   *
+   * This variable serves as a reference to a GsonBuilder that allows customization of the Gson instance,
+   * including registering custom type adapters, serializers, and deserializers, as well as adjusting serialization policies.
+   *
+   * The {@link #gsonBuilder} is primarily utilized when an existing {@link Gson} instance is not directly provided.
+   * It ensures that the adapter can defer the creation of a Gson object until it is explicitly required.
+   */
+  private GsonBuilder gsonBuilder;
+
+  /**
+   * Creates a new instance of {@code ExcludeFieldsAdapter} for managing the serialization and deserialization
+   * of objects of the specified {@code type}, while excluding certain fields during serialization.
+   *
+   * @param type           the class type of the objects to be serialized and deserialized
+   * @param excludedFields the set of field names to be excluded during serialization
+   * @param gson           the Gson instance to be used for serialization and deserialization
+   */
+  public ExcludeFieldsAdapter(Class<T> type, Set<String> excludedFields, Gson gson) {
+    this.type = type;
+    this.excludedFields = new HashSet<>(excludedFields);
+    this.gsonBuilder = null;
+    this.gson = gson;
+  }
+
+  /**
+   * Constructs an instance of {@code ExcludeFieldsAdapter} that selectively excludes specified fields from
+   * the JSON output based on the configuration provided during initialization.
+   *
+   * @param type the class of the type to be serialized and deserialized
+   * @param excludedFields a set of field names to be excluded from the serialized JSON output
+   * @param gsonBuilder an instance of {@code GsonBuilder} used to create a custom {@code Gson} instance if needed
+   */
+  public ExcludeFieldsAdapter(Class<T> type, Set<String> excludedFields, GsonBuilder gsonBuilder) {
+    this.type = type;
+    this.excludedFields = new HashSet<>(excludedFields);
+    this.gsonBuilder = gsonBuilder;
+    this.gson = null;
+  }
+
+  /**
+   * Lazily initializes and retrieves the {@link Gson} instance. If the instance is null, it creates a new {@link Gson}
+   * object using the {@link GsonBuilder} provided during the adapter's initialization.
+   *
+   * @return the {@link Gson} instance used for serialization and deserialization
+   */
+  private Gson getGson() {
+    if (gson == null) {
+      gson = gsonBuilder.create();
+    }
+    return gson;
+  }
+
+  /**
+   * Serializes an object of type {@code T} into JSON format, excluding certain fields specified during the initialization of this adapter.
+   * The object is first converted into a {@link JsonObject}, then the fields listed in the excluded fields set are removed from the JSON
+   * representation before writing it to the provided {@link JsonWriter}.
+   *
+   * @param out   the {@link JsonWriter} to write the serialized JSON data to
+   * @param value the object of type {@code T} to serialize into JSON
+   * @throws IOException if an I/O error occurs during writing
+   */
+  @Override
+  public void write(JsonWriter out, T value) throws IOException {
+    JsonObject obj = getGson().toJsonTree(value).getAsJsonObject();
+
+    for (String field : excludedFields) {
+      obj.remove(field);
+    }
+
+    Streams.write(obj, out);
+  }
+
+  /**
+   * Reads a JSON input stream and deserializes it into an object of the specified type.
+   *
+   * @param in the {@link JsonReader} to read the JSON input from
+   * @return an instance of type {@code T} deserialized from the JSON input
+   * @throws IOException if an error occurs during reading or deserialization
+   */
+  @Override
+  public T read(JsonReader in) throws IOException {
+    return getGson().fromJson(in, type);
+  }
+}