com.google.appengine.repackaged.com.google.common.flogger.util.StaticMethodCaller Maven / Gradle / Ivy
/*
* Copyright (C) 2019 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.util;
import java.lang.reflect.Method;
import org.checkerframework.checker.nullness.compatqual.NullableDecl;
/**
* Helper to call a no-arg constructor or static getter to obtain an instance of a specified type.
* This is used for logging platform "plugins". It is expected that these constructors/methods will
* be invoked once during logger initialization and then the results cached in the platform class
* (thus there is no requirement for the class being invoked to handle caching of the result).
*/
public final class StaticMethodCaller {
// TODO(cgdecker): Rename this class; eventually perhaps just roll it into DefaultPlatform
/**
* Attempts to get an instance of the given {@code type} that is specified by the given {@code
* propertyName}, returning {@code null} if that is not possible for any reason.
*
* The property's value, if present, is expected to be one of:
*
*
* - A fully-qualified class name, in which case the instance is obtained by invoking the
* class's no-arg static {@code getInstance} method, if present, or public no-arg
* constructor.
*
- A fully-qualified class name followed by {@code #} and a method name, in which case the
* instance is obtained by invoking a no-arg static method of that name, if present, or a
* public no-arg constructor if not present.
*
*/
public static T getInstanceFromSystemProperty(String propertyName, Class type) {
return getInstanceFromSystemProperty(propertyName, null, type);
}
/**
* Attempts to get an instance of the given {@code type} that is specified by the given {@code
* propertyName}, returning {@code null} if that is not possible for any reason.
*
* The property's value, if present, or the given {@code defaultValue}, is expected to be one
* of:
*
*
* - A fully-qualified class name, in which case the instance is obtained by invoking the
* class's no-arg static {@code getInstance} method, if present, or public no-arg
* constructor.
*
- A fully-qualified class name followed by {@code #} and a method name, in which case the
* instance is obtained by invoking a no-arg static method of that name, if present, or a
* public no-arg constructor if not present.
*
*/
@NullableDecl
public static T getInstanceFromSystemProperty(
String propertyName, @NullableDecl String defaultValue, Class type) {
String property = readProperty(propertyName, defaultValue);
if (property == null) {
return null;
}
int hashIndex = property.indexOf('#');
String className = hashIndex == -1 ? property : property.substring(0, hashIndex);
// TODO(cgdecker): Eventually we should eleminate method checks and only use constructors
String methodName = hashIndex == -1 ? "getInstance" : property.substring(hashIndex + 1);
String attemptedMethod = className + '#' + methodName + "()";
try {
Class clazz = Class.forName(className);
try {
Method method = clazz.getMethod(methodName);
// If the method exists, try to invoke it and don't fall back to the constructor if it
// fails. The fallback is only for the case where the method in question has been removed.
return type.cast(method.invoke(null));
} catch (NoSuchMethodException e) {
// If the user explicitly specified a getInstance method via "ClassName#getInstance" and
// that getInstance method doesn't exist, fall back to constructor invocation. This allows
// system properties that were set for service types Flogger provides to continue to work
// even though we intentionally removed their getInstance() methods.
if (hashIndex == -1 || !methodName.equals("getInstance")) {
// Otherwise, error and return
error("method '%s' does not exist: %s\n", property, e);
return null;
}
}
// The method didn't exist, try the constructor
attemptedMethod = "new " + className + "()";
return type.cast(clazz.getConstructor().newInstance());
} catch (ClassNotFoundException e) {
// Expected if an optional aspect is not being used (no error).
} catch (ClassCastException e) {
error("cannot cast result of calling '%s' to '%s': %s\n", attemptedMethod, type.getName(), e);
} catch (Exception e) {
// Catches SecurityException *and* ReflexiveOperationException (which doesn't exist in 1.6).
error(
"cannot call expected no-argument constructor or static method '%s': %s\n",
attemptedMethod, e);
}
return null;
}
private static String readProperty(String propertyName, @NullableDecl String defaultValue) {
Checks.checkNotNull(propertyName, "property name");
try {
return System.getProperty(propertyName, defaultValue);
} catch (SecurityException e) {
error("cannot read property name %s: %s", propertyName, e);
}
return null;
}
// This cannot use a fluent logger here and it's even risky to use a JDK logger.
private static void error(String msg, Object... args) {
System.err.println(StaticMethodCaller.class + ": " + String.format(msg, args));
}
private StaticMethodCaller() {}
}