I am reading spring boot source code, when I read this, I am confused.
/*
* Copyright 2012-2019 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
*
* https://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.autoconfigure;
import java.nio.charset.StandardCharsets;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicBoolean;
import javax.validation.Configuration;
import javax.validation.Validation;
import org.springframework.boot.context.event.ApplicationFailedEvent;
import org.springframework.boot.context.event.ApplicationReadyEvent;
import org.springframework.boot.context.event.ApplicationStartingEvent;
import org.springframework.boot.context.event.SpringApplicationEvent;
import org.springframework.boot.context.logging.LoggingApplicationListener;
import org.springframework.context.ApplicationListener;
import org.springframework.core.annotation.Order;
import org.springframework.format.support.DefaultFormattingConversionService;
import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;
import org.springframework.http.converter.support.AllEncompassingFormHttpMessageConverter;
/**
* {@link ApplicationListener} to trigger early initialization in a background thread of
* time consuming tasks.
* <p>
* Set the {@link #IGNORE_BACKGROUNDPREINITIALIZER_PROPERTY_NAME} system property to
* {@code true} to disable this mechanism and let such initialization happen in the
* foreground.
*
* @author Phillip Webb
* @author Andy Wilkinson
* @author Artsiom Yudovin
* @since 1.3.0
*/
@Order(LoggingApplicationListener.DEFAULT_ORDER + 1)
public class BackgroundPreinitializer implements ApplicationListener<SpringApplicationEvent> {
/**
* System property that instructs Spring Boot how to run pre initialization. When the
* property is set to {@code true}, no pre-initialization happens and each item is
* initialized in the foreground as it needs to. When the property is {@code false}
* (default), pre initialization runs in a separate thread in the background.
* @since 2.1.0
*/
public static final String IGNORE_BACKGROUNDPREINITIALIZER_PROPERTY_NAME = "spring.backgroundpreinitializer.ignore";
private static final AtomicBoolean preinitializationStarted = new AtomicBoolean(false);
private static final CountDownLatch preinitializationComplete = new CountDownLatch(1);
@Override
public void onApplicationEvent(SpringApplicationEvent event) {
if (!Boolean.getBoolean(IGNORE_BACKGROUNDPREINITIALIZER_PROPERTY_NAME)
&& event instanceof ApplicationStartingEvent && multipleProcessors()
&& preinitializationStarted.compareAndSet(false, true)) {
performPreinitialization();
}
if ((event instanceof ApplicationReadyEvent || event instanceof ApplicationFailedEvent)
&& preinitializationStarted.get()) {
try {
preinitializationComplete.await();
}
catch (InterruptedException ex) {
Thread.currentThread().interrupt();
}
}
}
private boolean multipleProcessors() {
return Runtime.getRuntime().availableProcessors() > 1;
}
private void performPreinitialization() {
try {
Thread thread = new Thread(new Runnable() {
@Override
public void run() {
runSafely(new ConversionServiceInitializer());
runSafely(new ValidationInitializer());
runSafely(new MessageConverterInitializer());
runSafely(new JacksonInitializer());
runSafely(new CharsetInitializer());
preinitializationComplete.countDown();
}
public void runSafely(Runnable runnable) {
try {
runnable.run();
}
catch (Throwable ex) {
// Ignore
}
}
}, "background-preinit");
thread.start();
}
catch (Exception ex) {
// This will fail on GAE where creating threads is prohibited. We can safely
// continue but startup will be slightly slower as the initialization will now
// happen on the main thread.
preinitializationComplete.countDown();
}
}
/**
* Early initializer for Spring MessageConverters.
*/
private static class MessageConverterInitializer implements Runnable {
@Override
public void run() {
new AllEncompassingFormHttpMessageConverter();
}
}
/**
* Early initializer for javax.validation.
*/
private static class ValidationInitializer implements Runnable {
@Override
public void run() {
Configuration<?> configuration = Validation.byDefaultProvider().configure();
configuration.buildValidatorFactory().getValidator();
}
}
/**
* Early initializer for Jackson.
*/
private static class JacksonInitializer implements Runnable {
@Override
public void run() {
Jackson2ObjectMapperBuilder.json().build();
}
}
/**
* Early initializer for Spring's ConversionService.
*/
private static class ConversionServiceInitializer implements Runnable {
@Override
public void run() {
new DefaultFormattingConversionService();
}
}
private static class CharsetInitializer implements Runnable {
@Override
public void run() {
StandardCharsets.UTF_8.name();
}
}
}
These lines:
/**
* Early initializer for Spring's ConversionService.
*/
private static class ConversionServiceInitializer implements Runnable {
@Override
public void run() {
new DefaultFormattingConversionService();
}
}
Why just new a DefaultFormattingConversionService object, but did not assign to any reference. what it affect?
I read some times source code, but still confused.
Who could help me, thanks advance!
Update:
I debugged, but still could not find anywhere retain the reference indirectly.
