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源码分析
本文源代码基于 Springboot 2.1.0
/*
* Copyright 2012-2018 the original author or 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 org.springframework.boot.context.logging;
import java.net.URLClassLoader;
import java.util.Arrays;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.boot.context.event.ApplicationEnvironmentPreparedEvent;
import org.springframework.boot.context.event.ApplicationFailedEvent;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.event.GenericApplicationListener;
import org.springframework.context.event.SmartApplicationListener;
import org.springframework.core.ResolvableType;
/**
* A GenericApplicationListener that reacts to
* ApplicationEnvironmentPreparedEvent environment prepared events and to
* ApplicationFailedEvent failed events by logging the classpath of the thread
* context class loader (TCCL) at DEBUG level.
*
* 在环境准备完成事件ApplicationEnvironmentPreparedEvent或者应用失败事件ApplicationFailedEvent
* 发生时,DEBUG级别日志输出线程上下文类加载器的classpath。
*
* 线程上下文类加载器:TCCL,thread context class loader
*
* 该类定义为GenericApplicationListener的原因是它要响应多种事件类型:
* ApplicationEnvironmentPreparedEvent类型和ApplicationFailedEvent类型
*
* @author Andy Wilkinson
* @since 2.0.0
*/
public final class ClasspathLoggingApplicationListener
implements GenericApplicationListener {
private static final int ORDER = LoggingApplicationListener.DEFAULT_ORDER + 1;
private static final Log logger = LogFactory
.getLog(ClasspathLoggingApplicationListener.class);
@Override
public void onApplicationEvent(ApplicationEvent event) {
// 仅在DEBUG级别日志进行输出
if (logger.isDebugEnabled()) {
if (event instanceof ApplicationEnvironmentPreparedEvent) {
logger.debug("Application started with classpath: " + getClasspath());
}
else if (event instanceof ApplicationFailedEvent) {
logger.debug(
"Application failed to start with classpath: " + getClasspath());
}
}
}
@Override
public int getOrder() {
return ORDER;
}
@Override
public boolean supportsEventType(ResolvableType resolvableType) {
Class<?> type = resolvableType.getRawClass();
if (type == null) {
return false;
}
return ApplicationEnvironmentPreparedEvent.class.isAssignableFrom(type)
|| ApplicationFailedEvent.class.isAssignableFrom(type);
}
private String getClasspath() {
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
if (classLoader instanceof URLClassLoader) {
return Arrays.toString(((URLClassLoader) classLoader).getURLs());
}
return "unknown";
}
}
输出类似于:
2018-11-17 18:54:05.382 DEBUG [main] org.springframework.boot.context.logging.ClasspathLoggingApplicationListener : Application started with classpath: […]