/* * Copyright (C) 2008 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;import java.lang.reflect.AccessibleObject;import java.lang.reflect.Field;import java.lang.reflect.Type;/** * Provides ability to apply a visitor to an object and all of its fields recursively. * * @author Inderjeet Singh * @author Joel Leitch */final class ObjectNavigator {  public interface Visitor {    /**     * This is called before the object navigator starts visiting the current object     */    void startVisitingObject(Object node);    /**     * This is called to visit the current object if it is an array     */    void visitArray(Object array, Type componentType);    /**     * This is called to visit an object field of the current object     */    void visitObjectField(Field f, Type typeOfF, Object obj);    /**     * This is called to visit an array field of the current object     */    void visitArrayField(Field f, Type typeOfF, Object obj);    /**     * This is called to visit an object using a custom handler     * @return true if a custom handler exists, false otherwise     */    public boolean visitUsingCustomHandler(Object obj, Type objType);    /**     * This is called to visit a field of the current object using a custom handler     */    public boolean visitFieldUsingCustomHandler(Field f, Type actualTypeOfField, Object parent);        /**     * Retrieve the current target     */    Object getTarget();  }  private final ExclusionStrategy exclusionStrategy;  private final MemoryRefStack<Object> ancestors;  private final Object obj;  private final Type objType;  /**   * @param obj The object being navigated   * @param objType The (fully genericized) type of the object being navigated   * @param exclusionStrategy the concrete strategy object to be used to   *        filter out fields of an object.   */  ObjectNavigator(Object obj, Type objType, ExclusionStrategy exclusionStrategy,      MemoryRefStack<Object> ancestors) {    Preconditions.checkNotNull(exclusionStrategy);    Preconditions.checkNotNull(ancestors);    this.obj = obj;    this.objType = objType;    this.exclusionStrategy = exclusionStrategy;    this.ancestors = ancestors;  }  /**   * Navigate all the fields of the specified object.   * If a field is null, it does not get visited.   */  public void accept(Visitor visitor) {    boolean visitedWithCustomHandler = visitor.visitUsingCustomHandler(obj, objType);    if (!visitedWithCustomHandler) {      Object objectToVisit = (obj == null) ? visitor.getTarget() : obj;      if (objectToVisit == null) {        return;      }      TypeInfo objTypeInfo = new TypeInfo(objType);      if (exclusionStrategy.shouldSkipClass(objTypeInfo.getRawClass())) {        return;      }        if (ancestors.contains(objectToVisit)) {        throw new IllegalStateException("Circular reference found: " + objectToVisit);      }      ancestors.push(objectToVisit);        try {        if (objTypeInfo.isArray()) {          visitor.visitArray(objectToVisit, objType);        } else {          visitor.startVisitingObject(objectToVisit);          // For all classes in the inheritance hierarchy (including the current class),          // visit all fields          for (Class<?> curr = objTypeInfo.getRawClass();          curr != null && !curr.equals(Object.class); curr = curr.getSuperclass()) {            if (!curr.isSynthetic()) {              navigateClassFields(objectToVisit, curr, visitor);            }          }        }      } finally {        ancestors.pop();      }    }  }  private void navigateClassFields(Object obj, Class<?> clazz, Visitor visitor) {    Field[] fields = clazz.getDeclaredFields();    AccessibleObject.setAccessible(fields, true);    for (Field f : fields) {      TypeInfo fieldTypeInfo = TypeInfoFactory.getTypeInfoForField(f, objType);      Type actualTypeOfField = fieldTypeInfo.getActualType();      if (exclusionStrategy.shouldSkipField(f)) {        continue; // skip      } else {        boolean visitedWithCustomHandler =           visitor.visitFieldUsingCustomHandler(f, actualTypeOfField, obj);        if (!visitedWithCustomHandler) {          if (fieldTypeInfo.isArray()) {            visitor.visitArrayField(f, actualTypeOfField, obj);          } else {            visitor.visitObjectField(f, actualTypeOfField, obj);          }        }      }    }  }}