我正在开发一个 Struts2 + Spring + Hibernate webapp，我需要在检索一个对象或该对象的集合后初始化一个惰性集合。
用例
我有一个team 模型，其中急切加载了一个名为employees 的关系(我认为很明显这是一个集合)。反过来，employee 模型有一个惰性关系 registry，我只需要它来执行某些特定操作，所以我根本不需要急切地加载它。
现在。我调用我 teamService (用 Spring 注入(inject)我的 Struts2 Controller )以检索特定的 teamItem已经加载了他的集合 employees。现在是时候为每个员工加载其注册表关系了。
使用 employeeService (这也用 Spring 注入(inject)了我的 Struts2 Controller )我调用 initializeCollections()他的 DAO 方法应该加载惰性集合调用
Hibernate.initialize(employee.getRegistry());
当我执行此操作时 org.hibernate.LazyInitializationException: could not initialize proxy - no Session抛出异常。
堆栈跟踪:
at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:167) ~[hibernate-core-3.6.10.Final.jar:3.6.10.Final]
at org.hibernate.Hibernate.initialize(Hibernate.java:414) ~[hibernate-core-3.6.10.Final.jar:3.6.10.Final]
at web.bkgd.simba.dao.registry.RegistryEmployeeDAO.initializeCollections(RegistryEmployeeDAO.java:438) ~[RegistryEmployeeDAO.class:?]
at web.bkgd.simba.service.abstractions.BaseService.initializeCollections(BaseService.java:142) ~[BaseService.class:?]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.7.0_79]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) ~[?:1.7.0_79]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.7.0_79]
at java.lang.reflect.Method.invoke(Method.java:606) ~[?:1.7.0_79]
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:317) ~[spring-aop-4.1.0.RELEASE.jar:4.1.0.RELEASE]
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:190) ~[spring-aop-4.1.0.RELEASE.jar:4.1.0.RELEASE]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157) ~[spring-aop-4.1.0.RELEASE.jar:4.1.0.RELEASE]
at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:98) ~[spring-tx-4.1.0.RELEASE.jar:4.1.0.RELEASE]
at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:266) ~[spring-tx-4.1.0.RELEASE.jar:4.1.0.RELEASE]
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:95) ~[spring-tx-4.1.0.RELEASE.jar:4.1.0.RELEASE]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.1.0.RELEASE.jar:4.1.0.RELEASE]
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:207) ~[spring-aop-4.1.0.RELEASE.jar:4.1.0.RELEASE]
at com.sun.proxy.$Proxy1302.initializeCollections(Unknown Source) ~[?:?]
at web.bkgd.simba.controller.ajax.agenda.TeamController.doSomething(TeamController.java:177) ~[AjaxTeamController.class:?]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.7.0_79]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) ~[?:1.7.0_79]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.7.0_79]
at java.lang.reflect.Method.invoke(Method.java:606) ~[?:1.7.0_79]
at ognl.OgnlRuntime.invokeMethod(OgnlRuntime.java:870) ~[ognl-3.0.6.jar:?]
at ognl.OgnlRuntime.callAppropriateMethod(OgnlRuntime.java:1293) ~[ognl-3.0.6.jar:?]
at ognl.ObjectMethodAccessor.callMethod(ObjectMethodAccessor.java:68) ~[ognl-3.0.6.jar:?]
at com.opensymphony.xwork2.ognl.accessor.XWorkMethodAccessor.callMethodWithDebugInfo(XWorkMethodAccessor.java:117) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.ognl.accessor.XWorkMethodAccessor.callMethod(XWorkMethodAccessor.java:108) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at ognl.OgnlRuntime.callMethod(OgnlRuntime.java:1369) ~[ognl-3.0.6.jar:?]
at ognl.ASTMethod.getValueBody(ASTMethod.java:90) ~[ognl-3.0.6.jar:?]
at ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:212) ~[ognl-3.0.6.jar:?]
at ognl.SimpleNode.getValue(SimpleNode.java:258) ~[ognl-3.0.6.jar:?]
at ognl.Ognl.getValue(Ognl.java:494) ~[ognl-3.0.6.jar:?]
at ognl.Ognl.getValue(Ognl.java:458) ~[ognl-3.0.6.jar:?]
at com.opensymphony.xwork2.ognl.OgnlUtil$2.execute(OgnlUtil.java:309) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.ognl.OgnlUtil.compileAndExecute(OgnlUtil.java:340) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.ognl.OgnlUtil.getValue(OgnlUtil.java:307) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:423) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:287) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:250) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at web.bkgd.simba.utility.interceptors.SessionCleanInterceptor.intercept(SessionCleanInterceptor.java:86) ~[SessionCleanInterceptor.class:?]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at org.apache.struts2.interceptor.DeprecationInterceptor.intercept(DeprecationInterceptor.java:41) ~[struts2-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:256) ~[struts2-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:167) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:265) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:76) ~[struts2-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:138) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:229) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:229) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:191) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:73) ~[struts2-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at org.apache.struts2.interceptor.DateTextFieldInterceptor.intercept(DateTextFieldInterceptor.java:125) ~[struts2-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:91) ~[struts2-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:253) ~[struts2-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:100) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:141) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:145) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:171) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:139) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164) ~[struts2-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:193) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) ~[xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:189) [xwork-core-2.3.24.1.jar:2.3.24.1]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) [xwork-core-2.3.24.1.jar:2.3.24.1]
at web.bkgd.simba.utility.interceptors.LoginInterceptor.intercept(LoginInterceptor.java:113) [LoginInterceptor.class:?]
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244) [xwork-core-2.3.24.1.jar:2.3.24.1]
at org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:54) [struts2-core-2.3.24.1.jar:2.3.24.1]
at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:564) [struts2-core-2.3.24.1.jar:2.3.24.1]
at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:81) [struts2-core-2.3.24.1.jar:2.3.24.1]
at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:99) [struts2-core-2.3.24.1.jar:2.3.24.1]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) [catalina.jar:7.0.61]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) [catalina.jar:7.0.61]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220) [catalina.jar:7.0.61]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122) [catalina.jar:7.0.61]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505) [catalina.jar:7.0.61]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170) [catalina.jar:7.0.61]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103) [catalina.jar:7.0.61]
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950) [catalina.jar:7.0.61]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116) [catalina.jar:7.0.61]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:423) [catalina.jar:7.0.61]
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1079) [tomcat-coyote.jar:7.0.61]
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:620) [tomcat-coyote.jar:7.0.61]
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318) [tomcat-coyote.jar:7.0.61]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) [?:1.7.0_79]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) [?:1.7.0_79]
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-coyote.jar:7.0.61]
at java.lang.Thread.run(Thread.java:745) [?:1.7.0_79]
编辑 01-12-2015
我已尝试按照 Predrag Maric 的回答进行操作，但由于似乎仍然无法正常工作，因此我需要进行一些修改。
所以:
- Implement Open Session in View pattern
没办法。此解决方案可能会导致非常深的关系加载，特别是对于 JSON 序列化。当然我总是可以定义 <param name="includeProperties">标记并加载我需要的内容，但我仍然有点害怕表演。
- Initialize whatever you need in the first service
这就是重点。为了实现这个功能，我改变了我的 Action 和 DAO 结构。我使用了一些反射来创建一个通用方法，我可以在我的应用程序的每个 DAO 中使用它。
它的工作原理非常简单:
示例
输入:
第一个字符串的方法只是调用Hibernate.initialize()方法和第二个拆分字符串以加载:
initializeRelations(relation.class, relation, "childRelation.grandChildRelation"); initializeRelations(childRelation.class, childRelation, "grandChildRelation"); 这里有代码:
团队 DAO
这些方法在从数据库加载团队 bean 或团队 bean 列表后调用
/**
* Initialize relations. This method returns true if a correct
* initialization of the relation has been made by hibernate, false in any
* other case. If the relations object is a List, the method recursively
* call himself in order to initialize every single instance of the list.
* If the relations string contains a "." it means that a grandchild
* relation has to be loaded.
*
* @param beanClass
* @param model
* @param relations
* @return boolean
*/
public boolean initializeRelations(Class beanClass, BaseModel model, Object relations) {
// Check if relations is a List
if (relations instanceof List) {
// Recursively call initializeRelations
for (String relation : (List<String>) relations) {
return initializeRelations(beanClass, model, relation);
}
} else if (relations instanceof String) {
// If relations contains "." then a grandChild relation has to be loaded.
if (((String) relations).contains(".")) {
String[] childRelations = ((String) relations).split("\\.");
// Initialize the child relation
Object newChildRelations = initializeRelation(beanClass, model, childRelations[0]);
if (newChildRelations == null) {
return false;
} else if (newChildRelations instanceof BaseModel) {
initializeRelations(newChildRelations.getClass(), model, (Object[]) Arrays.copyOfRange(childRelations, 1, childRelations.length));
} else if (newChildRelations instanceof List) {
for (Object newChildRelation : childRelations) {
initializeRelations(newChildRelation.getClass(), model, (Object[]) Arrays.copyOfRange(childRelations, 1, childRelations.length));
}
}
} else {
Object newChildRelations = initializeRelation(beanClass, model, (String) relations);
return newChildRelations == null;
}
}
return false;
}
private Object initializeRelation(Class beanClass, BaseModel model, String relation) {
try {
for (PropertyDescriptor pd : Introspector.getBeanInfo(beanClass).getPropertyDescriptors()) {
if (pd.getReadMethod() != null && !"class".equals(pd.getName()) && relation.toLowerCase().equals(pd.getName().toLowerCase()) && pd.getReadMethod().invoke(model) == null) {
Hibernate.initialize(pd.getReadMethod().invoke(model));
return pd.getReadMethod().invoke(model);
}
}
} catch (IntrospectionException ex) {
LOG.warn("Cannot initialize ralation", ex);
} catch (HibernateException | IllegalAccessException | IllegalArgumentException | InvocationTargetException ex) {
LOG.warn("Cannot initialize ralation", ex);
}
return null;
}
但是我在日志中看到的是只加载了第一个关系
[DEBUG] 01-12-2015 14:06:52 Controller - relation: Employee{data1="data1", data2="data2", data3="data3", data4="data4", data5="data5"}
[DEBUG] 01-12-2015 14:06:52 Controller - child: [!!!model.Registry_$$_javassist_17@75ce9b7d=>org.hibernate.LazyInitializationException:could not initialize proxy - no Session!!!]
最佳答案
几个月前我遇到了一些问题。 我已经解决了在我的 session 工厂构建器中设置参数的问题。
尝试将参数“hibernate.enable_lazy_load_no_trans”设置为您的 hibernate 配置。
sfBuilder.getProperties().put("hibernate.enable_lazy_load_no_trans",
"true");
这个参数解决了我的问题。希望对您有所帮助。
编辑: 谨慎使用。查看this post .
关于java - 初始化惰性集合，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/33955974/
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我正在阅读一本关于Ruby的书，作者在编写类初始化定义时使用的形式与他在本书前几节中使用的形式略有不同。它看起来像这样:classTicketattr_accessor:venue,:datedefinitialize(venue,date)self.venue=venueself.date=dateendend在本书的前几节中，它的定义如下:classTicketattr_accessor:venue,:datedefinitialize(venue,date)@venue=venue@date=dateendend在第一个示例中使用setter方法与在第二个示例中使用实例变量之间是
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我只想对我一直在思考的这个问题有其他意见，例如我有classuser_controller和classuserclassUserattr_accessor:name,:usernameendclassUserController//dosomethingaboutanythingaboutusersend问题是我的User类中是否应该有逻辑user=User.newuser.do_something(user1)oritshouldbeuser_controller=UserController.newuser_controller.do_something(user1,user2)我
什么是ruby的rack或python的Java的wsgi？还有一个路由库。 最佳答案 来自Python标准PEP333:Bycontrast,althoughJavahasjustasmanywebapplicationframeworksavailable,Java's"servlet"APImakesitpossibleforapplicationswrittenwithanyJavawebapplicationframeworktoruninanywebserverthatsupportstheservletAPI.ht
这篇文章是继上一篇文章“Observability：从零开始创建Java微服务并监控它（一）”的续篇。在上一篇文章中，我们讲述了如何创建一个Javaweb应用，并使用Filebeat来收集应用所生成的日志。在今天的文章中，我来详述如何收集应用的指标，使用APM来监控应用并监督web服务的在线情况。源码可以在地址 https://github.com/liu-xiao-guo/java_observability 进行下载。摄入指标指标被视为可以随时更改的时间点值。当前请求的数量可以改变任何毫秒。你可能有1000个请求的峰值，然后一切都回到一个请求。这也意味着这些指标可能不准确，你还想提取最小/
HashMap中为什么引入红黑树，而不是AVL树呢1.概述开始学习这个知识点之前我们需要知道，在JDK1.8以及之前，针对HashMap有什么不同。JDK1.7的时候，HashMap的底层实现是数组+链表JDK1.8的时候，HashMap的底层实现是数组+链表+红黑树我们要思考一个问题，为什么要从链表转为红黑树呢。首先先让我们了解下链表有什么不好？？？2.链表上述的截图其实就是链表的结构，我们来看下链表的增删改查的时间复杂度增：因为链表不是线性结构，所以每次添加的时候，只需要移动一个节点，所以可以理解为复杂度是N(1)删：算法时间复杂度跟增保持一致查：既然是非线性结构，所以查询某一个节点的时候