Testing Parameterized Type Handling Implementation in google/gson

google/gson

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

            
/*
 * Copyright (C) 2014 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.gson.internal;

import static com.google.common.truth.Truth.assertThat;
import static org.junit.Assert.assertThrows;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.List;
import java.util.Properties;
import org.junit.Test;

@SuppressWarnings("ClassNamedLikeTypeParameter") // for dummy classes A, B, ...
public final class GsonTypesTest {

  @Test
  public void testNewParameterizedTypeWithoutOwner() throws Exception {
    // List<A>. List is a top-level class
    ParameterizedType type = $Gson$Types.newParameterizedTypeWithOwner(null, List.class, A.class);
    assertThat(type.getOwnerType()).isNull();
    assertThat(type.getRawType()).isEqualTo(List.class);
    assertThat(type.getActualTypeArguments()).asList().containsExactly(A.class);

    // A<B>. A is a static inner class.
    type = $Gson$Types.newParameterizedTypeWithOwner(null, A.class, B.class);
    assertThat(getFirstTypeArgument(type)).isEqualTo(B.class);

    IllegalArgumentException e =
        assertThrows(
            IllegalArgumentException.class,
            // NonStaticInner<A> is not allowed without owner
            () -> $Gson$Types.newParameterizedTypeWithOwner(null, NonStaticInner.class, A.class));
    assertThat(e).hasMessageThat().isEqualTo("Must specify owner type for " + NonStaticInner.class);

    type =
        $Gson$Types.newParameterizedTypeWithOwner(
            GsonTypesTest.class, NonStaticInner.class, A.class);
    assertThat(type.getOwnerType()).isEqualTo(GsonTypesTest.class);
    assertThat(type.getRawType()).isEqualTo(NonStaticInner.class);
    assertThat(type.getActualTypeArguments()).asList().containsExactly(A.class);

    final class D {}

    // D<A> is allowed since D has no owner type
    type = $Gson$Types.newParameterizedTypeWithOwner(null, D.class, A.class);
    assertThat(type.getOwnerType()).isNull();
    assertThat(type.getRawType()).isEqualTo(D.class);
    assertThat(type.getActualTypeArguments()).asList().containsExactly(A.class);

    // A<D> is allowed.
    type = $Gson$Types.newParameterizedTypeWithOwner(null, A.class, D.class);
    assertThat(getFirstTypeArgument(type)).isEqualTo(D.class);
  }

  @Test
  public void testGetFirstTypeArgument() throws Exception {
    assertThat(getFirstTypeArgument(A.class)).isNull();

    Type type = $Gson$Types.newParameterizedTypeWithOwner(null, A.class, B.class, C.class);
    assertThat(getFirstTypeArgument(type)).isEqualTo(B.class);
  }

  private static final class A {}

  private static final class B {}

  private static final class C {}

  @SuppressWarnings({"ClassCanBeStatic", "UnusedTypeParameter"})
  private final class NonStaticInner<T> {}

  /**
   * Given a parameterized type {@code A<B, C>}, returns B. If the specified type is not a generic
   * type, returns null.
   */
  public static Type getFirstTypeArgument(Type type) throws Exception {
    if (!(type instanceof ParameterizedType)) {
      return null;
    }
    ParameterizedType ptype = (ParameterizedType) type;
    Type[] actualTypeArguments = ptype.getActualTypeArguments();
    if (actualTypeArguments.length == 0) {
      return null;
    }
    return $Gson$Types.canonicalize(actualTypeArguments[0]);
  }

  @Test
  public void testEqualsOnMethodTypeVariables() throws Exception {
    Method m1 = TypeVariableTest.class.getMethod("method");
    Method m2 = TypeVariableTest.class.getMethod("method");

    Type rt1 = m1.getGenericReturnType();
    Type rt2 = m2.getGenericReturnType();

    assertThat($Gson$Types.equals(rt1, rt2)).isTrue();
  }

  @Test
  public void testEqualsOnConstructorParameterTypeVariables() throws Exception {
    Constructor<TypeVariableTest> c1 = TypeVariableTest.class.getConstructor(Object.class);
    Constructor<TypeVariableTest> c2 = TypeVariableTest.class.getConstructor(Object.class);

    Type rt1 = c1.getGenericParameterTypes()[0];
    Type rt2 = c2.getGenericParameterTypes()[0];

    assertThat($Gson$Types.equals(rt1, rt2)).isTrue();
  }

  private static final class TypeVariableTest {

    @SuppressWarnings("unused")
    public <T> TypeVariableTest(T parameter) {}

    @SuppressWarnings({"unused", "TypeParameterUnusedInFormals"})
    public <T> T method() {
      return null;
    }
  }

  @Test
  public void testGetMapKeyAndValueTypesForPropertiesSubclass() throws Exception {
    class CustomProperties extends Properties {
      private static final long serialVersionUID = 4112578634029874840L;
    }

    Type[] types =
        $Gson$Types.getMapKeyAndValueTypes(CustomProperties.class, CustomProperties.class);

    assertThat(types[0]).isEqualTo(String.class);
    assertThat(types[1]).isEqualTo(String.class);
  }
}