Migration to Tomcat 8: InstanceAlreadyExistsExcept

问题:

I have a question about context config in Tomcat 8. I migrating project from Tomcat 7 to 8 and have unusual problem: if nothing change in config I caught an error:

    "2015-02-03 12:05:48,310 FIRST_ADMIN ERROR web.context.ContextLoader:331 
-> Context initialization failed org.springframework.jmx.export.UnableToRegisterMBeanException: 
    Unable to register MBean [org.apache.tomcat.dbcp.dbcp2.BasicDataSource@434990dd]
     with key 'dataSource'; nested exception is 
    javax.management.InstanceAlreadyExistsException:  
    Catalina:type=DataSource,host=localhost,context=/first-
    admin,class=javax.sql.DataSource,name="jdbc/datasource/first"

Part of context:

<Resource name="jdbc/datasource/first"
              auth="Container"
              type="javax.sql.DataSource"
              poolPreparedStatements="true"
              initialSize="25"
              maxActive="100"
              maxIdle="100"
              minIdle="25"
              username="us"
              password="pa"
              driverClassName="com.mysql.jdbc.Driver"
              validationQuery="select 1"
              testOnBorrow="true"
          url="jdbc:mysql://localhost:3306/firstproject?useUnicode=true&amp;characterEncoding=UTF-8&amp;profileSQL=false&amp;autoSlowLog=false&amp;slowQueryThresholdMillis=100&amp;autoReconnect=true"/>

So, it's works in tomcat 7 without any problem. In Tomcat 8 I can solve this problem in 2 ways:

1. By adding to resource: singleton = "false";
2. By adding to resource: factory="org.apache.tomcat.jdbc.pool.DataSourceFactory"

If I clearly understand tomcat creates datasource for my app and for jmx, but in Tomcat 7 it was single object, in Tomcat 8 it must be different. So my question is why that situation has happened? I couldn't find any information of this change in documentation. And I'm interesting what is better: create single datasource (I think so) or create several by factory.

回答1:

We had the same problem. We declared our data source as a spring bean, and it looks like both spring and the bean itself try to register an Mbean which leads to this conflict. All we had to do is configure our Mbean Exporter like this:

@Bean
public AnnotationMBeanExporter annotationMBeanExporter() {
    AnnotationMBeanExporter annotationMBeanExporter = new AnnotationMBeanExporter();
    annotationMBeanExporter.addExcludedBean("dataSource");
    return annotationMBeanExporter;
}

Although I suppose setting the registration policy to:

annotationMBeanExporter.setRegistrationPolicy(RegistrationPolicy.IGNORE_EXISTING);

might also work.

回答2:

I had the same error and resolved it by adding registration="ignoreExisting" to the mbean-export part:

<context:mbean-export server="mbeanServer" default-domain="mydomain" registration="ignoreExisting" />

回答3:

If you want the solution using annotations Spring boot already defines MBeanExporter bean so you can auto-wire on it

@Autowired
MBeanExporter mBeanExporter ;

Then change the registration policy

mBeanExporter.setRegistrationPolicy(RegistrationPolicy.IGNORE_EXISTING);

回答4:

If anybody uses applicationContext.xml style out there, I solved the issue like this:

<bean id="myNamedExporter" class="org.springframework.jmx.export.MBeanExporter">
    <property name="registrationPolicy" value="IGNORE_EXISTING" />
</bean>