com.google.appengine.repackaged.com.google.common.flogger.backend.system.BackendFactory Maven / Gradle / Ivy
/*
* Copyright (C) 2014 The Flogger Authors.
*
* 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 com.google.common.flogger.backend.system;
import com.google.common.flogger.backend.LoggerBackend;
/**
* An API to create logger backends for a given class name. This is implemented as an abstract class
* (rather than an interface) to reduce to risk of breaking existing implementations if the API
* changes.
*
* Essential Implementation Restrictions
*
* Any implementation of this API MUST follow the rules listed below to avoid any risk of
* re-entrant code calling during logger initialization. Failure to do so risks creating complex,
* hard to debug, issues with Flogger configuration.
*
*
* - Implementations MUST NOT attempt any logging in static methods or constructors.
*
- Implementations MUST NOT statically depend on any unknown code.
*
- Implementations MUST NOT depend on any unknown code in constructors.
*
*
* Note that logging and calling arbitrary unknown code (which might log) are permitted inside
* the instance methods of this API, since they are not called during platform initialization. The
* easiest way to achieve this is to simply avoid having any non-trivial static fields or any
* instance fields at all in the implementation.
*
*
While this sounds onerous it's not difficult to achieve because this API is a singleton, and
* can delay any actual work until its methods are called. For example if any additional state is
* required in the implementation, it can be held via a "lazy holder" to defer initialization.
*
*
This is a service type
*
* This type is considered a service type and implemenations may be loaded from the
* classpath via {@link java.util.ServiceLoader} provided the proper service metadata is included in
* the jar file containing the implementation. When creating an implementation of this class, you
* can provide serivce metadata (and thereby allow users to get your implementation just by
* including your jar file) by either manually including a {@code
* META-INF/services/com.google.common.flogger.backend.system.BackendFactory} file containing the
* name of your implementation class or by annotating your implementation class using
* {@code @AutoService(BackendFactory.class)}. See the documentation of both {@link
* java.util.ServiceLoader} and {@link DefaultPlatform} for more information.
*/
public abstract class BackendFactory {
/**
* Creates a logger backend of the given class name for use by a Fluent Logger. Note that the
* returned backend need not be unique; one backend could be used by multiple loggers. The given
* class name must be in the normal dot-separated form (e.g., "com.example.Foo$Bar") rather than
* the internal binary format "com/example/Foo$Bar").
*
* @param loggingClassName the fully-qualified name of the Java class to which the logger is
* associated. The logger name is derived from this string in a backend specific way.
*/
public abstract LoggerBackend create(String loggingClassName);
}