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@jacobtabak
Created January 4, 2016 15:42
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package com.dramafever.common.gson;
import com.google.gson.Gson;
import com.google.gson.TypeAdapter;
import com.google.gson.TypeAdapterFactory;
import com.google.gson.reflect.TypeToken;
public final class AutoValueTypeAdapterFactory implements TypeAdapterFactory {
private static final String AUTOVALUE_PREFIX = "AutoValue_";
@SuppressWarnings("unchecked")
@Override public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
Class<? super T> rawType = type.getRawType();
if (rawType.getSimpleName().startsWith(AUTOVALUE_PREFIX)) {
// This is an AutoValue generated class, delegate to the generated type adapter
return getTypeAdapter(rawType, gson);
} else {
// This isn't an AutoValue generated class, but it could be a class with the @AutoValue annotation.
if (rawType.isPrimitive()) {
return null;
} else {
// The AutoValue_ClassName class was found, now we must find the type adapter
String packageName = ((Class) type.getRawType()).getPackage().getName();
String autoValueClassSimpleName = AUTOVALUE_PREFIX +
rawType.getName().substring(packageName.length() + 1).replace('$', '_');
String autoValueClassName = packageName + "." + autoValueClassSimpleName;
try {
Class<?> autoValueClass = Class.forName(autoValueClassName);
return getTypeAdapter(autoValueClass, gson);
} catch (ClassNotFoundException ignored) {
// There is no AutoValue generated class for this class, return null
return null;
}
}
}
}
/**
* Gets the type adapter for the given AutoValue class. Recursively searches through AutoValue generated
* classes. It starts by looking for AutoValue_Class$ClassTypeAdapter, then $AutoValue_Class$ClassTypeAdapter
* until it finds the type adapter or crashes because something went terribly wrong.
* @param type the type, must be an AutoValue generated class, e.g. AutoValue_MyClass
* @param gson the gson instance
* @return the type
*/
TypeAdapter getTypeAdapter(Class type, Gson gson) {
if (!type.getSimpleName().startsWith(AUTOVALUE_PREFIX)) {
throw new IllegalArgumentException("This method can only retrieve the TypeAdapter for AutoValue classes");
}
return getTypeAdapter(type, gson, 0);
}
/**
* Recursive helper method for {@link #getTypeAdapter(Class, Gson)}
* @param type the type, must be an AutoValue generated class, e.g. AutoValue_MyClass
* @param gson the gson instance
* @param depth the type
* @return the type adapter
*/
private TypeAdapter getTypeAdapter(Class type, Gson gson, int depth) {
String autoValueClassName = getAutoValueClassNameWithExtensionDepth(type, depth);
int lastUnderscorePosition = type.getSimpleName().lastIndexOf("_");
String annotatedSimpleName = type.getSimpleName().substring(lastUnderscorePosition + 1);
String typeAdapterClassName = autoValueClassName + "$" + annotatedSimpleName + "TypeAdapter";
if (getClass(autoValueClassName) != null) {
Class typeAdapterClass = getClass(typeAdapterClassName);
if (typeAdapterClass != null) {
try {
//noinspection unchecked
TypeAdapter typeAdapter =
(TypeAdapter) typeAdapterClass.getDeclaredConstructor(Gson.class).newInstance(gson);
return typeAdapter.nullSafe();
} catch (Exception e) {
throw new RuntimeException("Failed to invoke the type adapter's constructor", e);
}
} else {
return getTypeAdapter(type, gson, depth + 1);
}
} else {
throw new RuntimeException("Reached the end fo the AutoValue extension chain for " +
autoValueClassName + " without finding a type adapter. Is autovalue-gson installed?");
}
}
/**
* Gets the AutoValue generated class with the given extension depth. Eg, for a class called AutoValue_MyClass
* and extension depth 2, this method would return $$AutoValue_MyClass.
* @param type the type, must be an AutoValue generated class, e.g. AutoValue_MyClass
* @param extensionDepth the extension depth
* @return the class name for the specified extension depth
*/
private String getAutoValueClassNameWithExtensionDepth(Class type, int extensionDepth) {
StringBuilder classPrefixBuilder = new StringBuilder();
for (int i = 1; i < extensionDepth; i++) {
classPrefixBuilder.append('$');
}
return type.getPackage().getName() + "." + classPrefixBuilder.toString() + type.getSimpleName();
}
/**
* Helper method to get a class, or return null if it doesn't exist rather than throwing an exception
* @param className the class name
* @return the class, or null if it didn't exist
*/
private Class getClass(String className) {
try {
return Class.forName(className);
} catch (ClassNotFoundException ignored) {
return null;
}
}
}
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