/*
* #%L
* FlatPack serialization code
* %%
* Copyright (C) 2012 Perka 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.
* #L%
*/
package com.getperka.flatpack.ext;
import static com.getperka.flatpack.util.FlatPackTypes.erase;
import static com.getperka.flatpack.util.FlatPackTypes.getSingleParameterization;
import com.getperka.flatpack.FlatPackVisitor;
import com.google.gson.JsonElement;
import com.google.gson.stream.JsonWriter;
/**
* Implements type-specific encoding and decoding mechanisms.
*
* @param <T> the type of data that the instance operates on
*/
public abstract class Codex<T> implements Walker<T> {
/**
* Memoizing this value for the path-tracking saves a non-trivial amount of wall-time.
*/
private final String simpleName;
private final Class<T> parameterization;
protected Codex() {
simpleName = getClass().getSimpleName();
parameterization = erase(getSingleParameterization(getClass(), Codex.class));
}
/**
* Visit a non-null value using the supplied visitor.
*
* @param visitor the visitor that is traversing the object graph
* @param value the value being traversed
* @param context allows mutation of the object graph
*/
public abstract void acceptNotNull(FlatPackVisitor visitor, T value, VisitorContext<T> context);
/**
* Returns {@code value} if it conforms to the {@code T} type parameter. Due to erasure, this
* method can only partially verify objects of a parameterized type.
*/
public T cast(Object value) {
return parameterization.cast(value);
}
/**
* Returns a type descriptor for the JSON structure created by the Codex implementation.
*/
public abstract Type describe();
/**
* Returns a suffix to append to properties of the Codex's type.
*/
public String getPropertySuffix() {
return "";
}
/**
* Returns {@code true} if the value is the default value for an uninitialized instance of a
* property with that value.
*/
public boolean isDefaultValue(T value) {
return value == null;
}
/**
* Reify the given {@link JsonElement} into a Java value. If {@code} element is {@null} or
* represents a Json {@code null} value, this method will return {@code null}, otherwise this
* method will delegate to {@link #readNotNull(JsonElement, DeserializationContext)}.
*
* @param element the element that contains the value to reify
* @param context contextual information for the deserialization process
* @return the requested value
*/
public T read(JsonElement element, DeserializationContext context) {
if (element == null || element.isJsonNull()) {
return null;
}
context.pushPath("(" + simpleName + ".read())");
try {
return readNotNull(element, context);
} catch (Exception e) {
context.fail(e);
return null;
} finally {
context.popPath();
}
}
/**
* Reify the given {@link JsonElement} into a Java value.
*
* @param element the element that contains the value to reify
* @param context contextual information for the deserialization process
* @return the requested value
* @throws Exception implementations of this method may throw arbitrary exceptions which will be
* reported by {@link #read(JsonElement, DeserializationContext)}
*/
public abstract T readNotNull(JsonElement element, DeserializationContext context)
throws Exception;
/**
* Visit a value using the supplied visitor.
* <p>
* The default implementation delegates to {@link #acceptNotNull} or calls
* {@link FlatPackVisitor#visitValue visitValue()} / {@link FlatPackVisitor#endVisitValue
* endVisitValue()} if {@code value} is {@code null}.
*
* @param visitor the visitor that is traversing the object graph
* @param value the value being traversed
* @param context allows mutation of the object graph
*/
@Override
public void walk(FlatPackVisitor visitor, T value, VisitorContext<T> context) {
if (value == null) {
visitor.visitValue(null, this, context);
visitor.endVisitValue(null, this, context);
} else {
acceptNotNull(visitor, value, context);
}
}
/**
* Write a value into the serialization context. If object is {@code null}, writes a null into
* {@link SerializationContext#getWriter()}, otherwise delegates to
* {@link #writeNotNull(Object, SerializationContext)}.
*
* @param object a value to write into {@link SerializationContext#getWriter()}
* @param context the serialization context
*/
public void write(T object, SerializationContext context) {
context.pushPath("(" + simpleName + ".write())");
try {
JsonWriter writer = context.getWriter();
if (object == null) {
writer.nullValue();
} else {
writeNotNull(object, context);
}
} catch (Exception e) {
context.fail(e);
} finally {
context.popPath();
}
}
/**
* Write a value into the serialization context.
*
* @param object a value to write into {@link SerializationContext#getWriter()}
* @param context the serialization context
* @throws Exception implementations of this method may throw arbitrary exceptions which will be
* reported by {@link #write(Object, SerializationContext)}
*/
public abstract void writeNotNull(T object, SerializationContext context) throws Exception;
}