com.cedarsoftware.util.io

Class JsonReader

java.lang.Object

com.cedarsoftware.util.io.JsonReader

All Implemented Interfaces:

Closeable, AutoCloseable

public class JsonReader
extends Object
implements Closeable

Read an object graph in JSON format and make it available in Java objects, or in a "Map of Maps." (untyped representation). This code handles cyclic references and can deserialize any Object graph without requiring a class to be 'Serializeable' or have any specific methods on it. It will handle classes with non public constructors.

Usages:

• Call the static method: JsonReader.jsonToJava(String json). This will return a typed Java object graph.
• Call the static method: JsonReader.jsonToMaps(String json). This will return an untyped object representation of the JSON String as a Map of Maps, where the fields are the Map keys, and the field values are the associated Map's values. You can call the JsonWriter.objectToJson() method with the returned Map, and it will serialize the Graph into the equivalent JSON stream from which it was read.
• Instantiate the JsonReader with an InputStream: JsonReader(InputStream in) and then call readObject(). Cast the return value of readObject() to the Java class that was the root of the graph.
• Instantiate the JsonReader with an InputStream: JsonReader(InputStream in, true) and then call readObject(). The return value will be a Map of Maps.

Author:

John DeRegnaucourt ([email protected])
Copyright (c) Cedar Software LLC

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.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	JsonReader.ClassFactory
static class	JsonReader.CollectionFactory Use to create new instances of collection interfaces (needed for empty collections)
static interface	JsonReader.JsonClassReader Implement this interface to add a custom JSON reader.
static class	JsonReader.MapFactory Use to create new instances of Map interfaces (needed for empty Maps)

Field Summary

Fields

Modifier and Type	Field and Description
protected static Set<Class>	notCustom
protected static Map<Class,JsonReader.JsonClassReader>	readers

Constructor Summary

Constructors

Constructor and Description
JsonReader()
JsonReader(InputStream inp)
JsonReader(InputStream inp, boolean useMaps)

Method Summary

Methods

Modifier and Type	Method and Description
static void	addNotCustomReader(Class c) Force json-io to use it's internal generic approach to writing the passed in class, even if a Custom JSON reader is specified for its parent class.
static void	addReader(Class c, JsonReader.JsonClassReader reader) Call this method to add your custom JSON reader to json-io.
static void	assignInstantiator(Class c, JsonReader.ClassFactory f) For difficult to instantiate classes, you can add your own ClassFactory which will be called when the passed in class 'c' is encountered.
void	close()
protected Object	convertParsedMapsToJava(JsonObject root) This method converts a root Map, (which contains nested Maps and so forth representing a Java Object graph), to a Java object instance.
static boolean	isLogicalPrimitive(Class c) Deprecated. Use MetaUtils.isLogicalPrimitive(c) instead.
static boolean	isPrimitive(Class c) Deprecated. Use MetaUtils.isPrimitive(c) instead.
Object	jsonObjectsToJava(JsonObject root) Convert a root JsonObject that represents parsed JSON, into an actual Java object.
static Object	jsonToJava(String json) Convert the passed in JSON string into a Java object graph.
static Map	jsonToMaps(String json) Convert the passed in JSON string into a Java object graph that consists solely of Java Maps where the keys are the fields and the values are primitives or other Maps (in the case of objects).
static Object	newInstance(Class c)
Object	readObject() Read JSON input from the stream that was set up in the constructor, turning it into Java Maps (JsonObject's).

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

readers

protected static final Map<Class,JsonReader.JsonClassReader> readers

notCustom

protected static final Set<Class> notCustom

Constructor Detail

JsonReader

public JsonReader()

JsonReader

public JsonReader(InputStream inp)

JsonReader

public JsonReader(InputStream inp,
          boolean useMaps)

Method Detail

assignInstantiator

public static void assignInstantiator(Class c,
                      JsonReader.ClassFactory f)

For difficult to instantiate classes, you can add your own ClassFactory which will be called when the passed in class 'c' is encountered. Your ClassFactory will be called with newInstance(c) and your factory is expected to return a new instance of 'c'. This API is an 'escape hatch' to allow ANY object to be instantiated by JsonReader and is useful when you encounter a class that JsonReader cannot instantiate using its internal exhausting attempts (trying all constructors, varying arguments to them, etc.)

Parameters:

c - Class to assign an ClassFactory to

f - ClassFactory that will create 'c' instances

addReader

public static void addReader(Class c,
             JsonReader.JsonClassReader reader)

Call this method to add your custom JSON reader to json-io. It will associate the Class 'c' to the reader you pass in. The readers are found with isAssignableFrom(). If this is too broad, causing too many classes to be associated to the custom reader, you can indicate that json-io should not use a custom reader, by calling the addNotCustomReader() method.

Parameters:

c - Class to assign a custom JSON reader to

reader - The JsonClassReader which will read the custom JSON format of 'c'

addNotCustomReader

public static void addNotCustomReader(Class c)

Force json-io to use it's internal generic approach to writing the passed in class, even if a Custom JSON reader is specified for its parent class.

Parameters:

c - Class to which to force no custom JSON reading to occur. Normally, this is not needed, however, if a reader is assigned to a parent class of 'c', then calling this method on 'c' will prevent any custom reader from processing class 'c'

jsonToJava

public static Object jsonToJava(String json)

Convert the passed in JSON string into a Java object graph.

Parameters:

json - String JSON input

Returns:

Java object graph matching JSON input

jsonToMaps

public static Map jsonToMaps(String json)

Convert the passed in JSON string into a Java object graph that consists solely of Java Maps where the keys are the fields and the values are primitives or other Maps (in the case of objects).

Parameters:

json - String JSON input

Returns:

Java object graph of Maps matching JSON input, or null if an error occurred.

readObject

public Object readObject()

Read JSON input from the stream that was set up in the constructor, turning it into Java Maps (JsonObject's). Then, if requested, the JsonObjects can be converted into Java instances.

Returns:

Java Object graph constructed from InputStream supplying JSON serialized content.

jsonObjectsToJava

public Object jsonObjectsToJava(JsonObject root)

Convert a root JsonObject that represents parsed JSON, into an actual Java object.

Parameters:

root - JsonObject instance that was the root object from the JSON input that was parsed in an earlier call to JsonReader.

Returns:

a typed Java instance that was serialized into JSON.

convertParsedMapsToJava

protected Object convertParsedMapsToJava(JsonObject root)

This method converts a root Map, (which contains nested Maps and so forth representing a Java Object graph), to a Java object instance. The root map came from using the JsonReader to parse a JSON graph (using the API that puts the graph into Maps, not the typed representation).

Parameters:

root - JsonObject instance that was the root object from the JSON input that was parsed in an earlier call to JsonReader.

Returns:

a typed Java instance that was serialized into JSON.

newInstance

public static Object newInstance(Class c)

close

public void close()

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

isPrimitive

@Deprecated
public static boolean isPrimitive(Class c)

Deprecated. Use MetaUtils.isPrimitive(c) instead.

Parameters:

c - Class to check

Returns:

boolean true if the passed in class is a Java primitive.

isLogicalPrimitive

@Deprecated
public static boolean isLogicalPrimitive(Class c)

Deprecated. Use MetaUtils.isLogicalPrimitive(c) instead.

Parameters:

c - Class to check

Returns:

boolean true if the passed in class is a Logical Java primitive. This adds Class, Date, String, and the primitive wrappers to the list.