/*
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* Copyright (C) 2011 Google Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package cn.emay.sdk.util.json.gson;
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import java.io.IOException;
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import java.io.Reader;
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import java.io.StringReader;
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import java.io.StringWriter;
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import java.io.Writer;
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import cn.emay.sdk.util.json.gson.internal.bind.JsonTreeReader;
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import cn.emay.sdk.util.json.gson.internal.bind.JsonTreeWriter;
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import cn.emay.sdk.util.json.gson.stream.JsonReader;
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import cn.emay.sdk.util.json.gson.stream.JsonToken;
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import cn.emay.sdk.util.json.gson.stream.JsonWriter;
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/**
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* Converts Java objects to and from JSON.
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*
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* <h3>Defining a type's JSON form</h3> By default Gson converts application
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* classes to JSON using its built-in type adapters. If Gson's default JSON
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* conversion isn't appropriate for a type, extend this class to customize the
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* conversion. Here's an example of a type adapter for an (X,Y) coordinate
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* point:
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*
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* <pre>
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* {
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* @code
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*
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* public class PointAdapter extends TypeAdapter<Point> {
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* public Point read(JsonReader reader) throws IOException {
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* if (reader.peek() == JsonToken.NULL) {
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* reader.nextNull();
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* return null;
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* }
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* String xy = reader.nextString();
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* String[] parts = xy.split(",");
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* int x = Integer.parseInt(parts[0]);
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* int y = Integer.parseInt(parts[1]);
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* return new Point(x, y);
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* }
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*
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* public void write(JsonWriter writer, Point value) throws IOException {
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* if (value == null) {
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* writer.nullValue();
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* return;
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* }
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* String xy = value.getX() + "," + value.getY();
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* writer.value(xy);
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* }
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* }
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* }
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* </pre>
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*
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* With this type adapter installed, Gson will convert {@code Points} to JSON as
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* strings like {@code "5,8"} rather than objects like {@code {"x":5,"y":8}}. In
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* this case the type adapter binds a rich Java class to a compact JSON value.
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*
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* <p>
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* The {@link #read(JsonReader) read()} method must read exactly one value and
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* {@link #write(JsonWriter,Object) write()} must write exactly one value. For
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* primitive types this is means readers should make exactly one call to
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* {@code nextBoolean()}, {@code nextDouble()}, {@code nextInt()}, {@code
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* nextLong()}, {@code nextString()} or {@code nextNull()}. Writers should make
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* exactly one call to one of <code>value()</code> or <code>nullValue()</code>.
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* For arrays, type adapters should start with a call to {@code beginArray()},
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* convert all elements, and finish with a call to {@code endArray()}. For
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* objects, they should start with {@code beginObject()}, convert the object,
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* and finish with {@code endObject()}. Failing to convert a value or converting
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* too many values may cause the application to crash.
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*
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* <p>
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* Type adapters should be prepared to read null from the stream and write it to
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* the stream. Alternatively, they should use {@link #nullSafe()} method while
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* registering the type adapter with Gson. If your {@code Gson} instance has
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* been configured to {@link GsonBuilder#serializeNulls()}, these nulls will be
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* written to the final document. Otherwise the value (and the corresponding
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* name when writing to a JSON object) will be omitted automatically. In either
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* case your type adapter must handle null.
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*
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* <p>
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* To use a custom type adapter with Gson, you must <i>register</i> it with a
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* {@link GsonBuilder}:
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*
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* <pre>
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* {@code
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*
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* GsonBuilder builder = new GsonBuilder();
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* builder.registerTypeAdapter(Point.class, new PointAdapter());
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* // if PointAdapter didn't check for nulls in its read/write methods, you should instead use
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* // builder.registerTypeAdapter(Point.class, new PointAdapter().nullSafe());
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* ...
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* Gson gson = builder.create();
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* }
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* </pre>
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*
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* @since 2.1
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*/
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// non-Javadoc:
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//
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// <h3>JSON Conversion</h3>
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// <p>A type adapter registered with Gson is automatically invoked while
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// serializing
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// or deserializing JSON. However, you can also use type adapters directly to
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// serialize
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// and deserialize JSON. Here is an example for deserialization: <pre> {@code
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//
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// String json = "{'origin':'0,0','points':['1,2','3,4']}";
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// TypeAdapter<Graph> graphAdapter = gson.getAdapter(Graph.class);
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// Graph graph = graphAdapter.fromJson(json);
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// }</pre>
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// And an example for serialization: <pre> {@code
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//
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// Graph graph = new Graph(...);
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// TypeAdapter<Graph> graphAdapter = gson.getAdapter(Graph.class);
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// String json = graphAdapter.toJson(graph);
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// }</pre>
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//
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// <p>Type adapters are <strong>type-specific</strong>. For example, a {@code
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// TypeAdapter<Date>} can convert {@code Date} instances to JSON and JSON to
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// instances of {@code Date}, but cannot convert any other types.
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//
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public abstract class TypeAdapter<T> {
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/**
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* Writes one JSON value (an array, object, string, number, boolean or null) for
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* {@code value}.
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*
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* @param value
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* the Java object to write. May be null.
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*/
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public abstract void write(JsonWriter out, T value) throws IOException;
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/**
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* Converts {@code value} to a JSON document and writes it to {@code out}.
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* Unlike Gson's similar {@link Gson#toJson(JsonElement, Appendable) toJson}
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* method, this write is strict. Create a {@link JsonWriter#setLenient(boolean)
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* lenient} {@code JsonWriter} and call
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* {@link #write(com.google.gson.stream.JsonWriter, Object)} for lenient
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* writing.
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*
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* @param value
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* the Java object to convert. May be null.
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* @since 2.2
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*/
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public final void toJson(Writer out, T value) throws IOException {
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JsonWriter writer = new JsonWriter(out);
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write(writer, value);
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}
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/**
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* This wrapper method is used to make a type adapter null tolerant. In general,
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* a type adapter is required to handle nulls in write and read methods. Here is
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* how this is typically done:<br>
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*
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* <pre>
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* {
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* @code
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*
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* Gson gson = new GsonBuilder().registerTypeAdapter(Foo.class, new TypeAdapter<Foo>() {
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* public Foo read(JsonReader in) throws IOException {
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* if (in.peek() == JsonToken.NULL) {
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* in.nextNull();
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* return null;
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* }
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* // read a Foo from in and return it
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* }
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*
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* public void write(JsonWriter out, Foo src) throws IOException {
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* if (src == null) {
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* out.nullValue();
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* return;
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* }
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* // write src as JSON to out
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* }
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* }).create();
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* }
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* </pre>
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*
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* You can avoid this boilerplate handling of nulls by wrapping your type
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* adapter with this method. Here is how we will rewrite the above example:
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*
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* <pre>
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* {
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* @code
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*
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* Gson gson = new GsonBuilder().registerTypeAdapter(Foo.class, new TypeAdapter<Foo>() {
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* public Foo read(JsonReader in) throws IOException {
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* // read a Foo from in and return it
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* }
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*
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* public void write(JsonWriter out, Foo src) throws IOException {
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* // write src as JSON to out
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* }
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* }.nullSafe()).create();
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* }
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* </pre>
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*
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* Note that we didn't need to check for nulls in our type adapter after we used
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* nullSafe.
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*/
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public final TypeAdapter<T> nullSafe() {
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return new TypeAdapter<T>() {
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@Override
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public void write(JsonWriter out, T value) throws IOException {
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if (value == null) {
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out.nullValue();
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} else {
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TypeAdapter.this.write(out, value);
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}
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}
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@Override
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public T read(JsonReader reader) throws IOException {
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if (reader.peek() == JsonToken.NULL) {
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reader.nextNull();
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return null;
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}
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return TypeAdapter.this.read(reader);
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}
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};
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}
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/**
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* Converts {@code value} to a JSON document. Unlike Gson's similar
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* {@link Gson#toJson(Object) toJson} method, this write is strict. Create a
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* {@link JsonWriter#setLenient(boolean) lenient} {@code JsonWriter} and call
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* {@link #write(com.google.gson.stream.JsonWriter, Object)} for lenient
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* writing.
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*
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* @param value
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* the Java object to convert. May be null.
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* @since 2.2
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*/
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public final String toJson(T value) {
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StringWriter stringWriter = new StringWriter();
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try {
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toJson(stringWriter, value);
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} catch (IOException e) {
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throw new AssertionError(e); // No I/O writing to a StringWriter.
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}
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return stringWriter.toString();
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}
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/**
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* Converts {@code value} to a JSON tree.
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*
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* @param value
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* the Java object to convert. May be null.
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* @return the converted JSON tree. May be {@link JsonNull}.
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* @since 2.2
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*/
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public final JsonElement toJsonTree(T value) {
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try {
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JsonTreeWriter jsonWriter = new JsonTreeWriter();
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write(jsonWriter, value);
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return jsonWriter.get();
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} catch (IOException e) {
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throw new JsonIOException(e);
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}
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}
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/**
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* Reads one JSON value (an array, object, string, number, boolean or null) and
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* converts it to a Java object. Returns the converted object.
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*
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* @return the converted Java object. May be null.
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*/
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public abstract T read(JsonReader in) throws IOException;
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/**
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* Converts the JSON document in {@code in} to a Java object. Unlike Gson's
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* similar {@link Gson#fromJson(java.io.Reader, Class) fromJson} method, this
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* read is strict. Create a {@link JsonReader#setLenient(boolean) lenient}
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* {@code JsonReader} and call {@link #read(JsonReader)} for lenient reading.
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*
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* @return the converted Java object. May be null.
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* @since 2.2
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*/
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public final T fromJson(Reader in) throws IOException {
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JsonReader reader = new JsonReader(in);
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return read(reader);
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}
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/**
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* Converts the JSON document in {@code json} to a Java object. Unlike Gson's
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* similar {@link Gson#fromJson(String, Class) fromJson} method, this read is
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* strict. Create a {@link JsonReader#setLenient(boolean) lenient} {@code
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* JsonReader} and call {@link #read(JsonReader)} for lenient reading.
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*
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* @return the converted Java object. May be null.
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* @since 2.2
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*/
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public final T fromJson(String json) throws IOException {
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return fromJson(new StringReader(json));
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}
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/**
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* Converts {@code jsonTree} to a Java object.
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*
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* @param jsonTree
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* the Java object to convert. May be {@link JsonNull}.
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* @since 2.2
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*/
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public final T fromJsonTree(JsonElement jsonTree) {
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try {
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JsonReader jsonReader = new JsonTreeReader(jsonTree);
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return read(jsonReader);
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} catch (IOException e) {
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throw new JsonIOException(e);
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}
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}
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}
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