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Java example source code file (NullPointerTester.java)

This example Java source code file (NullPointerTester.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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Java - Java tags/keywords

annotation, class, immutablelist, invokable, iterable, method, nullpointertester, object, override, parameterizedtype, reflection, signature, suppresswarnings, threading, threads, typetoken, util, visibility

The NullPointerTester.java Java example source code

/*
 * Copyright (C) 2005 The Guava Authors
 *
 * 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.common.testing;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Converter;
import com.google.common.base.Objects;
import com.google.common.collect.ClassToInstanceMap;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;
import com.google.common.collect.Maps;
import com.google.common.collect.MutableClassToInstanceMap;
import com.google.common.reflect.Invokable;
import com.google.common.reflect.Parameter;
import com.google.common.reflect.Reflection;
import com.google.common.reflect.TypeToken;

import junit.framework.Assert;
import junit.framework.AssertionFailedError;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Member;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.ConcurrentMap;

import javax.annotation.Nullable;

/**
 * A test utility that verifies that your methods and constructors throw {@link
 * NullPointerException} or {@link UnsupportedOperationException} whenever null
 * is passed to a parameter that isn't annotated with {@link Nullable}.
 *
 * <p>The tested methods and constructors are invoked -- each time with one
 * parameter being null and the rest not null -- and the test fails if no
 * expected exception is thrown. {@code NullPointerTester} uses best effort to
 * pick non-null default values for many common JDK and Guava types, and also
 * for interfaces and public classes that have public parameter-less
 * constructors. When the non-null default value for a particular parameter type
 * cannot be provided by {@code NullPointerTester}, the caller can provide a
 * custom non-null default value for the parameter type via {@link #setDefault}.
 *
 * @author Kevin Bourrillion
 * @since 10.0
 */
@Beta
@GwtIncompatible
public final class NullPointerTester {

  private final ClassToInstanceMap<Object> defaults =
      MutableClassToInstanceMap.create();
  private final List<Member> ignoredMembers = Lists.newArrayList();

  private ExceptionTypePolicy policy = ExceptionTypePolicy.NPE_OR_UOE;

  /**
   * Sets a default value that can be used for any parameter of type
   * {@code type}. Returns this object.
   */
  public <T> NullPointerTester setDefault(Class type, T value) {
    defaults.putInstance(type, checkNotNull(value));
    return this;
  }

  /**
   * Ignore {@code method} in the tests that follow. Returns this object.
   *
   * @since 13.0
   */
  public NullPointerTester ignore(Method method) {
    ignoredMembers.add(checkNotNull(method));
    return this;
  }

  /**
   * Runs {@link #testConstructor} on every constructor in class {@code c} that
   * has at least {@code minimalVisibility}.
   */
  public void testConstructors(Class<?> c, Visibility minimalVisibility) {
    for (Constructor<?> constructor : c.getDeclaredConstructors()) {
      if (minimalVisibility.isVisible(constructor) && !isIgnored(constructor)) {
        testConstructor(constructor);
      }
    }
  }

  /**
   * Runs {@link #testConstructor} on every public constructor in class {@code
   * c}.
   */
  public void testAllPublicConstructors(Class<?> c) {
    testConstructors(c, Visibility.PUBLIC);
  }

  /**
   * Runs {@link #testMethod} on every static method of class {@code c} that has
   * at least {@code minimalVisibility}, including those "inherited" from
   * superclasses of the same package.
   */
  public void testStaticMethods(Class<?> c, Visibility minimalVisibility) {
    for (Method method : minimalVisibility.getStaticMethods(c)) {
      if (!isIgnored(method)) {
        testMethod(null, method);
      }
    }
  }

  /**
   * Runs {@link #testMethod} on every public static method of class {@code c},
   * including those "inherited" from superclasses of the same package.
   */
  public void testAllPublicStaticMethods(Class<?> c) {
    testStaticMethods(c, Visibility.PUBLIC);
  }

  /**
   * Runs {@link #testMethod} on every instance method of the class of
   * {@code instance} with at least {@code minimalVisibility}, including those
   * inherited from superclasses of the same package.
   */
  public void testInstanceMethods(Object instance, Visibility minimalVisibility) {
    for (Method method : getInstanceMethodsToTest(instance.getClass(), minimalVisibility)) {
      testMethod(instance, method);
    }
  }

  ImmutableList<Method> getInstanceMethodsToTest(Class c, Visibility minimalVisibility) {
    ImmutableList.Builder<Method> builder = ImmutableList.builder();
    for (Method method : minimalVisibility.getInstanceMethods(c)) {
      if (!isIgnored(method)) {
        builder.add(method);
      }
    }
    return builder.build();
  }

  /**
   * Runs {@link #testMethod} on every public instance method of the class of
   * {@code instance}, including those inherited from superclasses of the same
   * package.
   */
  public void testAllPublicInstanceMethods(Object instance) {
    testInstanceMethods(instance, Visibility.PUBLIC);
  }

  /**
   * Verifies that {@code method} produces a {@link NullPointerException}
   * or {@link UnsupportedOperationException} whenever <i>any of its
   * non-{@link Nullable} parameters are null.
   *
   * @param instance the instance to invoke {@code method} on, or null if
   *     {@code method} is static
   */
  public void testMethod(@Nullable Object instance, Method method) {
    Class<?>[] types = method.getParameterTypes();
    for (int nullIndex = 0; nullIndex < types.length; nullIndex++) {
      testMethodParameter(instance, method, nullIndex);
    }
  }

  /**
   * Verifies that {@code ctor} produces a {@link NullPointerException} or
   * {@link UnsupportedOperationException} whenever <i>any of its
   * non-{@link Nullable} parameters are null.
   */
  public void testConstructor(Constructor<?> ctor) {
    Class<?> declaringClass = ctor.getDeclaringClass();
    checkArgument(Modifier.isStatic(declaringClass.getModifiers())
        || declaringClass.getEnclosingClass() == null,
        "Cannot test constructor of non-static inner class: %s", declaringClass.getName());
    Class<?>[] types = ctor.getParameterTypes();
    for (int nullIndex = 0; nullIndex < types.length; nullIndex++) {
      testConstructorParameter(ctor, nullIndex);
    }
  }

  /**
   * Verifies that {@code method} produces a {@link NullPointerException} or
   * {@link UnsupportedOperationException} when the parameter in position {@code
   * paramIndex} is null.  If this parameter is marked {@link Nullable}, this
   * method does nothing.
   *
   * @param instance the instance to invoke {@code method} on, or null if
   *     {@code method} is static
   */
  public void testMethodParameter(
      @Nullable final Object instance, final Method method, int paramIndex) {
    method.setAccessible(true);
    testParameter(instance, invokable(instance, method), paramIndex, method.getDeclaringClass());
  }

  /**
   * Verifies that {@code ctor} produces a {@link NullPointerException} or
   * {@link UnsupportedOperationException} when the parameter in position {@code
   * paramIndex} is null.  If this parameter is marked {@link Nullable}, this
   * method does nothing.
   */
  public void testConstructorParameter(Constructor<?> ctor, int paramIndex) {
    ctor.setAccessible(true);
    testParameter(null, Invokable.from(ctor), paramIndex, ctor.getDeclaringClass());
  }

  /** Visibility of any method or constructor. */
  public enum Visibility {

    PACKAGE {
      @Override boolean isVisible(int modifiers) {
        return !Modifier.isPrivate(modifiers);
      }
    },

    PROTECTED {
      @Override boolean isVisible(int modifiers) {
        return Modifier.isPublic(modifiers) || Modifier.isProtected(modifiers);
      }
    },

    PUBLIC {
      @Override boolean isVisible(int modifiers) {
        return Modifier.isPublic(modifiers);
      }
    };

    abstract boolean isVisible(int modifiers);

    /**
     * Returns {@code true} if {@code member} is visible under {@code this}
     * visibility.
     */
    final boolean isVisible(Member member) {
      return isVisible(member.getModifiers());
    }

    final Iterable<Method> getStaticMethods(Class cls) {
      ImmutableList.Builder<Method> builder = ImmutableList.builder();
      for (Method method : getVisibleMethods(cls)) {
        if (Invokable.from(method).isStatic()) {
          builder.add(method);
        }
      }
      return builder.build();
    }

    final Iterable<Method> getInstanceMethods(Class cls) {
      ConcurrentMap<Signature, Method> map = Maps.newConcurrentMap();
      for (Method method : getVisibleMethods(cls)) {
        if (!Invokable.from(method).isStatic()) {
          map.putIfAbsent(new Signature(method), method);
        }
      }
      return map.values();
    }

    private ImmutableList<Method> getVisibleMethods(Class cls) {
      // Don't use cls.getPackage() because it does nasty things like reading
      // a file.
      String visiblePackage = Reflection.getPackageName(cls);
      ImmutableList.Builder<Method> builder = ImmutableList.builder();
      for (Class<?> type : TypeToken.of(cls).getTypes().classes().rawTypes()) {
        if (!Reflection.getPackageName(type).equals(visiblePackage)) {
          break;
        }
        for (Method method : type.getDeclaredMethods()) {
          if (!method.isSynthetic() && isVisible(method)) {
            builder.add(method);
          }
        }
      }
      return builder.build();
    }
  }

  private static final class Signature {
    private final String name;
    private final ImmutableList<Class parameterTypes;

    Signature(Method method) {
      this(method.getName(), ImmutableList.copyOf(method.getParameterTypes()));
    }

    Signature(String name, ImmutableList<Class parameterTypes) {
      this.name = name;
      this.parameterTypes = parameterTypes;
    }

    @Override public boolean equals(Object obj) {
      if (obj instanceof Signature) {
        Signature that = (Signature) obj;
        return name.equals(that.name)
            && parameterTypes.equals(that.parameterTypes);
      }
      return false;
    }

    @Override public int hashCode() {
      return Objects.hashCode(name, parameterTypes);
    }
  }

  /**
   * Verifies that {@code invokable} produces a {@link NullPointerException} or
   * {@link UnsupportedOperationException} when the parameter in position {@code
   * paramIndex} is null.  If this parameter is marked {@link Nullable}, this
   * method does nothing.
   *
   * @param instance the instance to invoke {@code invokable} on, or null if
   *     {@code invokable} is static
   */
  private void testParameter(Object instance, Invokable<?, ?> invokable,
      int paramIndex, Class<?> testedClass) {
    if (isPrimitiveOrNullable(invokable.getParameters().get(paramIndex))) {
      return; // there's nothing to test
    }
    Object[] params = buildParamList(invokable, paramIndex);
    try {
      @SuppressWarnings("unchecked") // We'll get a runtime exception if the type is wrong.
      Invokable<Object, ?> unsafe = (Invokable) invokable;
      unsafe.invoke(instance, params);
      Assert.fail("No exception thrown for parameter at index " + paramIndex
          + " from " + invokable + Arrays.toString(params) + " for " + testedClass);
    } catch (InvocationTargetException e) {
      Throwable cause = e.getCause();
      if (policy.isExpectedType(cause)) {
        return;
      }
      AssertionFailedError error =
          new AssertionFailedError(
              String.format(
                  "wrong exception thrown from %s when passing null to %s parameter at index %s.%n"
                      + "Full parameters: %s%n"
                      + "Actual exception message: %s",
                  invokable,
                  invokable.getParameters().get(paramIndex).getType(),
                  paramIndex,
                  Arrays.toString(params),
                  cause));
      error.initCause(cause);
      throw error;
    } catch (IllegalAccessException e) {
      throw new RuntimeException(e);
    }
  }

  private Object[] buildParamList(Invokable<?, ?> invokable, int indexOfParamToSetToNull) {
    ImmutableList<Parameter> params = invokable.getParameters();
    Object[] args = new Object[params.size()];

    for (int i = 0; i < args.length; i++) {
      Parameter param = params.get(i);
      if (i != indexOfParamToSetToNull) {
        args[i] = getDefaultValue(param.getType());
        Assert.assertTrue(
            "Can't find or create a sample instance for type '"
                + param.getType()
                + "'; please provide one using NullPointerTester.setDefault()",
            args[i] != null || isNullable(param));
      }
    }
    return args;
  }

  private <T> T getDefaultValue(TypeToken type) {
    // We assume that all defaults are generics-safe, even if they aren't,
    // we take the risk.
    @SuppressWarnings("unchecked")
    T defaultValue = (T) defaults.getInstance(type.getRawType());
    if (defaultValue != null) {
      return defaultValue;
    }
    @SuppressWarnings("unchecked") // All arbitrary instances are generics-safe
    T arbitrary = (T) ArbitraryInstances.get(type.getRawType());
    if (arbitrary != null) {
      return arbitrary;
    }
    if (type.getRawType() == Class.class) {
      // If parameter is Class<? extends Foo>, we return Foo.class
      @SuppressWarnings("unchecked")
      T defaultClass = (T) getFirstTypeParameter(type.getType()).getRawType();
      return defaultClass;
    }
    if (type.getRawType() == TypeToken.class) {
      // If parameter is TypeToken<? extends Foo>, we return TypeToken.
      @SuppressWarnings("unchecked")
      T defaultType = (T) getFirstTypeParameter(type.getType());
      return defaultType;
    }
    if (type.getRawType() == Converter.class) {
      TypeToken<?> convertFromType = type.resolveType(
          Converter.class.getTypeParameters()[0]);
      TypeToken<?> convertToType = type.resolveType(
          Converter.class.getTypeParameters()[1]);
      @SuppressWarnings("unchecked") // returns default for both F and T
      T defaultConverter = (T) defaultConverter(convertFromType, convertToType);
      return defaultConverter;
    }
    if (type.getRawType().isInterface()) {
      return newDefaultReturningProxy(type);
    }
    return null;
  }

  private <F, T> Converter defaultConverter(
      final TypeToken<F> convertFromType, final TypeToken convertToType) {
    return new Converter<F, T>() {
      @Override protected T doForward(F a) {
        return doConvert(convertToType);
      }
      @Override protected F doBackward(T b) {
        return doConvert(convertFromType);
      }

      private /*static*/ <S> S doConvert(TypeToken type) {
        return checkNotNull(getDefaultValue(type));
      }
    };
  }

  private static TypeToken<?> getFirstTypeParameter(Type type) {
    if (type instanceof ParameterizedType) {
      return TypeToken.of(
          ((ParameterizedType) type).getActualTypeArguments()[0]);
    } else {
      return TypeToken.of(Object.class);
    }
  }

  private <T> T newDefaultReturningProxy(final TypeToken type) {
    return new DummyProxy() {
      @Override <R> R dummyReturnValue(TypeToken returnType) {
        return getDefaultValue(returnType);
      }
    }.newProxy(type);
  }

  private static Invokable<?, ?> invokable(@Nullable Object instance, Method method) {
    if (instance == null) {
      return Invokable.from(method);
    } else {
      return TypeToken.of(instance.getClass()).method(method);
    }
  }

  static boolean isPrimitiveOrNullable(Parameter param) {
    return param.getType().getRawType().isPrimitive() || isNullable(param);
  }

  private static boolean isNullable(Parameter param) {
    return param.isAnnotationPresent(Nullable.class);
  }

  private boolean isIgnored(Member member) {
    return member.isSynthetic() || ignoredMembers.contains(member);
  }

  /**
   * Strategy for exception type matching used by {@link NullPointerTester}.
   */
  private enum ExceptionTypePolicy {

    /**
     * Exceptions should be {@link NullPointerException} or
     * {@link UnsupportedOperationException}.
     */
    NPE_OR_UOE() {
      @Override
      public boolean isExpectedType(Throwable cause) {
        return cause instanceof NullPointerException
            || cause instanceof UnsupportedOperationException;
      }
    },

    /**
     * Exceptions should be {@link NullPointerException},
     * {@link IllegalArgumentException}, or
     * {@link UnsupportedOperationException}.
     */
    NPE_IAE_OR_UOE() {
      @Override
      public boolean isExpectedType(Throwable cause) {
        return cause instanceof NullPointerException
            || cause instanceof IllegalArgumentException
            || cause instanceof UnsupportedOperationException;
      }
    };

    public abstract boolean isExpectedType(Throwable cause);
  }
}

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