背景
springboot越来越多的被大家所使用SpringBoot DevTool实现热部署
出现了相同类castException
分析
首先确定出现相同类的castException比如是由于classloader不同造成的。
一个class是否相同取决于两个因素
即不同classloader解释出来的class是不同的class
我们在学习jdbc的时候常见的使用
/** * Returns the {@code Class} object associated with the class or * interface with the given string name. Invoking this method is * equivalent to: * * <blockquote> * {@code Class.forName(className, true, currentLoader)} * </blockquote> * * where {@code currentLoader} denotes the defining class loader of * the current class. * * <p> For example, the following code fragment returns the * runtime {@code Class} descriptor for the class named * {@code java.lang.Thread}: * * <blockquote> * {@code Class t = Class.forName("java.lang.Thread")} * </blockquote> * <p> * A call to {@code forName("X")} causes the class named * {@code X} to be initialized. * * @param className the fully qualified name of the desired class. * @return the {@code Class} object for the class with the * specified name. * @exception LinkageError if the linkage fails * @exception ExceptionInInitializerError if the initialization provoked * by this method fails * @exception ClassNotFoundException if the class cannot be located */public static Class<?> forName(String className) throws ClassNotFoundException { return forName0(className, true, ClassLoader.getCallerClassLoader());}从上面我们可以了解不同的classloader解释的相同class也无法互相转换
这样我们把目标放在devtools上。
我们在springboot中引入了如下依赖
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-devtools</artifactId> <optional>true</optional></dependency>
那么如何排除devtool的依赖呢？
在application.properties中增加
spring.devtools.restart.enabled=false
发现启动时仍然可以看出使用的restartedMain
2018-03-19 22:04:37.641 INFO 53428 --- [restartedMain] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@7443f7a3: startup date [Mon Mar 19 22:03:34 CST 2018]; root of context hierarchy
2018-03-19 22:04:37.654 INFO 53428 --- [restartedMain] s.w.s.m.m.a.RequestMappingHandlerAdapter : Detected ResponseBodyAdvice bean in org.springframework.boot.actuate.autoconfigure.EndpointWebMvcHypermediaManagementContextConfiguration$ActuatorEndpointLinksAdvice
2018-03-19 22:04:37.956 INFO 53428 --- [restartedMain] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/swagger-ui.html] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-03-19 22:04:37.956 INFO 53428 --- [restartedMain] o.s.w.s.handler.SimpleUrlHandlerMapping
这边线程名为restartedMain 为啥设置spring.devtools.restart.enabled 无效呢？
代码
在对应devtools的包中使用了ApplicationListener
private void onApplicationStartingEvent(ApplicationStartingEvent event) { // It's too early to use the Spring environment but we should still allow // users to disable restart using a System property. String enabled = System.getProperty(ENABLED_PROPERTY); if (enabled == null || Boolean.parseBoolean(enabled)) { String[] args = event.getArgs(); DefaultRestartInitializer initializer = new DefaultRestartInitializer(); boolean restartOnInitialize = !AgentReloader.isActive(); Restarter.initialize(args, false, initializer, restartOnInitialize); } else { Restarter.disable(); }}很明显其实restarter的开启是从系统变量中读取 而并非从spring的环境中读取 正如注释所说 其实此刻使用spring的property还太早
因此可以使用系统变量
因此我们可以使用jvm参数
-Dspring.devtools.restart.enabled=false
果然此时一切就OK了
2018-03-19 22:18:12.928 INFO 66260 --- [main] com.f6car.base.Application : The following profiles are active: dev
2018-03-19 22:18:13.131 INFO 66260 --- [main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@2a4354cb: startup date [Mon Mar 19 22:18:13 CST 2018]; root of context hierarchy
那在Spring的配置文件中配置的目的是啥呢？
/** * Restart properties. */public static class Restart { private static final String DEFAULT_RESTART_EXCLUDES = "META-INF/maven/**," + "META-INF/resources/**,resources/**,static/**,public/**,templates/**," + "**/*Test.class,**/*Tests.class,git.properties,META-INF/build-info.properties"; private static final long DEFAULT_RESTART_POLL_INTERVAL = 1000; private static final long DEFAULT_RESTART_QUIET_PERIOD = 400; /** * Enable automatic restart. */ private boolean enabled = true; /** * Patterns that should be excluded from triggering a full restart. */ private String exclude = DEFAULT_RESTART_EXCLUDES; /** * Additional patterns that should be excluded from triggering a full restart. */ private String additionalExclude; /** * Amount of time (in milliseconds) to wait between polling for classpath changes. */ private long pollInterval = DEFAULT_RESTART_POLL_INTERVAL; /** * Amount of quiet time (in milliseconds) required without any classpath changes * before a restart is triggered. */ private long quietPeriod = DEFAULT_RESTART_QUIET_PERIOD; /** * Name of a specific file that when changed will trigger the restart check. If * not specified any classpath file change will trigger the restart. */ private String triggerFile; /** * Additional paths to watch for changes. */ private List<File> additionalPaths = new ArrayList<File>(); public boolean isEnabled() { return this.enabled; } public void setEnabled(boolean enabled) { this.enabled = enabled; }从代码中看到似乎是用来配置是否监听能否自动重启
/** * Local Restart Configuration. */ @ConditionalOnProperty(prefix = "spring.devtools.restart", name = "enabled", matchIfMissing = true) static class RestartConfiguration { @Autowired private DevToolsProperties properties; @EventListener public void onClassPathChanged(ClassPathChangedEvent event) { if (event.isRestartRequired()) { Restarter.getInstance().restart( new FileWatchingFailureHandler(fileSystemWatcherFactory())); } } @Bean @ConditionalOnMissingBean public ClassPathFileSystemWatcher classPathFileSystemWatcher() { URL[] urls = Restarter.getInstance().getInitialUrls(); ClassPathFileSystemWatcher watcher = new ClassPathFileSystemWatcher( fileSystemWatcherFactory(), classPathRestartStrategy(), urls); watcher.setStopWatcherOnRestart(true); return watcher; } @Bean @ConditionalOnMissingBean public ClassPathRestartStrategy classPathRestartStrategy() { return new PatternClassPathRestartStrategy( this.properties.getRestart().getAllExclude()); } @Bean public HateoasObjenesisCacheDisabler hateoasObjenesisCacheDisabler() { return new HateoasObjenesisCacheDisabler(); } @Bean public FileSystemWatcherFactory fileSystemWatcherFactory() { return new FileSystemWatcherFactory() { @Override public FileSystemWatcher getFileSystemWatcher() { return newFileSystemWatcher(); } }; } private FileSystemWatcher newFileSystemWatcher() { Restart restartProperties = this.properties.getRestart(); FileSystemWatcher watcher = new FileSystemWatcher(true, restartProperties.getPollInterval(), restartProperties.getQuietPeriod()); String triggerFile = restartProperties.getTriggerFile(); if (StringUtils.hasLength(triggerFile)) { watcher.setTriggerFilter(new TriggerFileFilter(triggerFile)); } List<File> additionalPaths = restartProperties.getAdditionalPaths(); for (File path : additionalPaths) { watcher.addSourceFolder(path.getAbsoluteFile()); } return watcher; } } }整个根据该配置来返回是否注册对应的watchService
当然我们也可以移除该jar
需要注意的是 当将这一段代码注释时 需要重新
mvn clean
否则有可能无法自动排除该jar
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持武林网。