JsonVisitor.java

/*
 * Copyright 2015 Red Hat, Inc. and/or its affiliates.
 *
 * 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 org.dashbuilder.json;

/**
 * A visitor for JSON objects. For each unique JSON datatype, a callback is
 * invoked with a {@link org.dashbuilder.json.JsonContext}
 * that can be used to replace a value or remove it. For Object and Array
 * types, the {@link #visitKey} and {@link #visitIndex} methods are invoked
 * respectively for each contained value to determine if they should be
 * processed or not. Finally, the visit methods for Object and Array types
 * returns a boolean that determines whether or not to process its contained
 * values.
 */
class JsonVisitor {

    private class ImmutableJsonContext extends JsonContext {

        public ImmutableJsonContext(JsonValue node) {
            super(node);
        }

        @Override
        public void removeMe() {
            immutableError();
        }

        @Override
        public void replaceMe(double d) {
            immutableError();
        }

        @Override
        public void replaceMe(String d) {
            immutableError();
        }

        @Override
        public void replaceMe(boolean d) {
            immutableError();
        }

        @Override
        public void replaceMe(JsonValue value) {
            immutableError();
        }

        private void immutableError() {
            throw new UnsupportedOperationException("Immutable context");
        }
    }

    public void accept(JsonValue node) {
        accept(node, new ImmutableJsonContext(node));
    }

    /**
     * Accept array or object type and visit its members.
     */
    public void accept(JsonValue node, JsonContext ctx) {
        if (node == null) {
            return;
        }
        node.traverse(this, ctx);
    }

    /**
     * Called after every element of array has been visited.
     */
    public void endVisit(JsonArray array, JsonContext ctx) {
    }

    /**
     * Called after every field of an object has been visited.
     * @param object
     * @param ctx
     */
    public void endVisit(JsonObject object, JsonContext ctx) {
    }

    /**
     * Called for JS numbers present in a JSON object.
     */
    public void visit(double number, JsonContext ctx) {
    }

    /**
     * Called for JS strings present in a JSON object.
     */
    public void visit(String string, JsonContext ctx) {
    }

    /**
     * Called for JS boolean present in a JSON object.
     */
    public void visit(boolean bool, JsonContext ctx) {
    }

    /**
     * Called for JS arrays present in a JSON object. Return true if array
     * elements should be visited.
     * @param array a JS array
     * @param ctx a context to replace or delete the array
     * @return true if the array elements should be visited
     */
    public boolean visit(JsonArray array, JsonContext ctx) {
        return true;
    }

    /**
     * Called for JS objects present in a JSON object. Return true if object
     * fields should be visited.
     * @param object a Json object
     * @param ctx a context to replace or delete the object
     * @return true if object fields should be visited
     */
    public boolean visit(JsonObject object, JsonContext ctx) {
        return true;
    }

    /**
     * Return true if the value for a given array index should be visited.
     * @param index an index in a JSON array
     * @param ctx a context object used to delete or replace values
     * @return true if the value associated with the index should be visited
     */
    public boolean visitIndex(int index, JsonContext ctx) {
        return true;
    }

    /**
     * Return true if the value for a given object key should be visited.
     * @param key a key in a JSON object
     * @param ctx a context object used to delete or replace values
     * @return true if the value associated with the key should be visited
     */
    public boolean visitKey(String key, JsonContext ctx) {
        return true;
    }

    /**
     * Called for nulls present in a JSON object.
     */
    public void visitNull(JsonContext ctx) {
    }
}