为什么在Apache中通过Spring配置Flexy会导致NoSuchElementException

Question

我有一个基于阿帕奇风暴 (1.1.1)的应用程序，它使用Spring (5.0.3)配置和注入基于Hibernate (5.2.12)的数据库服务，这些服务连接到PostgreSQL数据库。

在Hibernate和数据库之间，我将柔性池 (2.0.0)配置在HikariCP (2.7.6)之上，作为数据源(参见图A)。该应用程序是在一些Ubuntu16.04LTS服务器实例上使用最新的OpenJDK 8版本启动的。

​

​

在启动我的flexy-pool拓扑之后，我经历了与Storm相关的可悲的运行时异常。但是，这是而不是确定性的。有时它会起作用，有时会抛出下面的异常。如果我没有在我的应用程序中使用flexy-pool (参见图B)，那么一切都按预期的方式工作。

Caused by: 
 org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.vladmihalcea.flexypool.config.Configuration]: Factory method 'build' threw exception; nested exception is java.util.NoSuchElementException at 
org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:185) at 
org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:579) ... 42 more  
Caused by: 
 java.util.NoSuchElementException at 
sun.misc.URLClassPath$1.nextElement(URLClassPath.java:282) at 
sun.misc.URLClassPath$1.nextElement(URLClassPath.java:256) at 
java.net.URLClassLoader$3$1.run(URLClassLoader.java:603) at 
java.net.URLClassLoader$3$1.run(URLClassLoader.java:599) at 
java.security.AccessController.doPrivileged(Native Method) at 
java.net.URLClassLoader$3.next(URLClassLoader.java:598) at 
java.net.URLClassLoader$3.hasMoreElements(URLClassLoader.java:623) at 
sun.misc.CompoundEnumeration.next(CompoundEnumeration.java:45) at 
sun.misc.CompoundEnumeration.nextElement(CompoundEnumeration.java:58) at 
java.util.ServiceLoader$LazyIterator.hasNextService(ServiceLoader.java:357) at 
java.util.ServiceLoader$LazyIterator.hasNext(ServiceLoader.java:393) at 
java.util.ServiceLoader$1.hasNext(ServiceLoader.java:474) at 
com.vladmihalcea.flexypool.metric.MetricsFactoryResolver.resolve(MetricsFactoryResolver.java:27) at 
com.vladmihalcea.flexypool.config.Configuration$Builder.build(Configuration.java:165) at 
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at 
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at 
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at 
java.lang.reflect.Method.invoke(Method.java:498) at 
org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154)

图B中使用的Spring配置是这个配置(基于官方的示例)：

<bean id="hikariConfig" class="com.zaxxer.hikari.HikariConfig">
    <property name="poolName" value="springHikariCP"/>
    <property name="connectionTestQuery" value="SELECT 1"/>
    <property name="dataSourceClassName" value="${gmetric.dataSourceClassName}"/>
    <property name="dataSourceProperties">
        <props>
            <prop key="url">${shc.gmetric.url}</prop>
            <prop key="user">${shc.gmetric.username}</prop>
            <prop key="password">${shc.gmetric.pw}</prop>
        </props>
    </property>
</bean>

<bean id="poolingDataSource" class="com.zaxxer.hikari.HikariDataSource" destroy-method="close">
    <constructor-arg ref="hikariConfig"/>
</bean>

<bean id="configurationBuilder" class="com.vladmihalcea.flexypool.config.Configuration$Builder">
    <constructor-arg value="uniqueId"/>
    <constructor-arg ref="poolingDataSource"/>
    <constructor-arg value="#{ T(com.vladmihalcea.flexypool.adaptor.HikariCPPoolAdapter).FACTORY }"/>
</bean>

<bean id="configuration" factory-bean="configurationBuilder" factory-method="build"/>

<bean id="flexyPoolDataSource" class="com.vladmihalcea.flexypool.FlexyPoolDataSource" init-method="start" destroy-method="stop">
    <constructor-arg ref="configuration"/>
    <constructor-arg>
        <array>
            <bean class="com.vladmihalcea.flexypool.strategy.IncrementPoolOnTimeoutConnectionAcquiringStrategy.Factory">
                <constructor-arg value="5"/>
            </bean>
            <bean class="com.vladmihalcea.flexypool.strategy.RetryConnectionAcquiringStrategy.Factory">
                <constructor-arg value="2"/>
            </bean>
        </array>
    </constructor-arg>
</bean>

<bean id="entityManagerFactoryGMetrics"
      class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
    <property name="dataSource" ref="flexyPoolDataSource"/>
    <property name="persistenceUnitName" value="${gmetric.context.name}"/>
    <property name="jpaVendorAdapter">
        <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
            <!--<property name="generateDdl" value="true" />-->
            <property name="databasePlatform" value="${hibernate.dialect}"/>
            <property name="showSql" value="${hibernate.showSQL}"/>
        </bean>
    </property>
    <property name="jpaProperties">
        <props>
            <prop key="hibernate.connection.driver_class">${gmetric.driverClassName}</prop>
            <prop key="hibernate.dialect">${hibernate.dialect}</prop>
            <prop key="hibernate.show_sql">${hibernate.showSQL}</prop>
            <prop key="hibernate.hbm2ddl.auto">${hibernate.hbm2ddl.auto}</prop>
            <prop key="hibernate.current_session_context_class">thread</prop>
        </props>
    </property>
</bean>

我的问题是：

1. flexy-pool的基于Spring的(默认)配置正确吗？
2. 是否有防止与flexy-pool相关的运行时异常的解决方案？
3. 这个NoSuchElementException的原因是什么？

Answer 1

我发现，在我的阴影下的jar中缺少了Dropwizard度量4 (这是flexy-pool所必需的)，因此出现了这个有线运行时异常：

<dependency>
    <groupId>io.dropwizard.metrics</groupId>
    <artifactId>metrics-core</artifactId>
    <version>${metrics.version}</version>
</dependency>

根据作者，这与flexy-pool检测相关Dropwizard Metrics处理程序的方式有关(因为它支持DM3和DM4，这两种处理程序不能互换使用)。