Tomcat7中的JMX使用（二）Dynamic MBean

接触过动态MBean的朋友一定知道，它的实例肯定要实现一个接口，即javax.management.DynamicMBean。实现这个接口就意味着同时要实现它下面的6个方法：

Java代码

public Object getAttribute(String attribute) throws AttributeNotFoundException,MBeanException, ReflectionException;
public void setAttribute(Attribute attribute) throws AttributeNotFoundException,InvalidAttributeValueException, MBeanException, ReflectionException ;
public AttributeList getAttributes(String[] attributes);
public AttributeList setAttributes(AttributeList attributes);
public Object invoke(String actionName, Object params[], String signature[]) throws MBeanException, ReflectionException ;
public MBeanInfo getMBeanInfo();

public Object getAttribute(String attribute) throws AttributeNotFoundException,MBeanException, ReflectionException; public void setAttribute(Attribute attribute) throws AttributeNotFoundException,InvalidAttributeValueException, MBeanException, ReflectionException ; public AttributeList getAttributes(String[] attributes); public AttributeList setAttributes(AttributeList attributes); public Object invoke(String actionName, Object params[], String signature[]) throws MBeanException, ReflectionException ; public MBeanInfo getMBeanInfo();

通过实现这个通用接口，jvm允许程序在运行时获取和设置MBean公开的属性和调用MBean上公开的方法。

上面简要介绍了动态MBean的实现方式，Tomcat中的实际情况比这个要复杂。因为要生成很多种MBean，如果每种类型都用代码写一个MBean就失去了动态MBean的威力，Tomcat7中实际是通过配置文件（即每个组件所在的包下面的mbeans-descriptors.xml）结合通用的动态MBean（org.apache.tomcat.util.modeler.BaseModelMBean）、描述MBean配置信息的org.apache.tomcat.util.modeler.ManagedBean来简化MBean的构造。（笔者注：实际就是用动态MBean实现了模型MBean的功能）

一般情况下动态MBean的产生分为两个阶段：一、加载org.apache.tomcat.util.modeler.ManagedBean对象，二、注册MBean实例。

1.加载org.apache.tomcat.util.modeler.ManagedBean对象

在Tomcat启动时加载的配置文件server.xml中有这么一行配置：

Xml代码

<Listener className='org.apache.catalina.mbeans.GlobalResourcesLifecycleListener' />

因此在Tomcat启动时将加载这个类，在这个类中有一个静态成员变量registry：

Java代码

/**
* The configuration information registry for our managed beans.
*/
protected static Registry registry = MBeanUtils.createRegistry();

/** * The configuration information registry for our managed beans. */ protected static Registry registry = MBeanUtils.createRegistry();

也就是说类加载时registry就会获得Registry类的实例，这个Registry类很重要，在MBean的构造过程中将会多次涉及这个类里的方法。先看看MBeanUtils.createRegistry()方法：

Java代码

/**
* Create and configure (if necessary) and return the registry of
* managed object descriptions.
*/
public static synchronized Registry createRegistry() {
if (registry == null) {
registry = Registry.getRegistry(null, null);
ClassLoader cl = MBeanUtils.class.getClassLoader();
registry.loadDescriptors('org.apache.catalina.mbeans', cl);
registry.loadDescriptors('org.apache.catalina.authenticator', cl);
registry.loadDescriptors('org.apache.catalina.core', cl);
registry.loadDescriptors('org.apache.catalina', cl);
registry.loadDescriptors('org.apache.catalina.deploy', cl);
registry.loadDescriptors('org.apache.catalina.loader', cl);
registry.loadDescriptors('org.apache.catalina.realm', cl);
registry.loadDescriptors('org.apache.catalina.session', cl);
registry.loadDescriptors('org.apache.catalina.startup', cl);
registry.loadDescriptors('org.apache.catalina.users', cl);
registry.loadDescriptors('org.apache.catalina.ha', cl);
registry.loadDescriptors('org.apache.catalina.connector', cl);
registry.loadDescriptors('org.apache.catalina.valves', cl);
}
return (registry);
}

/** * Create and configure (if necessary) and return the registry of * managed object descriptions. */ public static synchronized Registry createRegistry() { if (registry == null) { registry = Registry.getRegistry(null, null); ClassLoader cl = MBeanUtils.class.getClassLoader(); registry.loadDescriptors('org.apache.catalina.mbeans', cl); registry.loadDescriptors('org.apache.catalina.authenticator', cl); registry.loadDescriptors('org.apache.catalina.core', cl); registry.loadDescriptors('org.apache.catalina', cl); registry.loadDescriptors('org.apache.catalina.deploy', cl); registry.loadDescriptors('org.apache.catalina.loader', cl); registry.loadDescriptors('org.apache.catalina.realm', cl); registry.loadDescriptors('org.apache.catalina.session', cl); registry.loadDescriptors('org.apache.catalina.startup', cl); registry.loadDescriptors('org.apache.catalina.users', cl); registry.loadDescriptors('org.apache.catalina.ha', cl); registry.loadDescriptors('org.apache.catalina.connector', cl); registry.loadDescriptors('org.apache.catalina.valves', cl); } return (registry); }

注意第8行Registry.getRegistry(null, null)方法的调用，看下它的实现就会发现返回的实际是Registry类的静态变量，这种调用后面会多次看到。接着还需要看一下MBeanUtils类的registry的定义：

Java代码

/**
* The configuration information registry for our managed beans.
*/
private static Registry registry = createRegistry();

/** * The configuration information registry for our managed beans. */ private static Registry registry = createRegistry();

因为此时MBeanUtils类还没在JVM里面加载过，它的成员变量registry为null，所以会调用Registry.getRegistry(null, null)方法构造对象，接下来会多次调用loadDescriptors方法，以下面这一句代码为例：

Java代码

registry.loadDescriptors('org.apache.catalina.connector', cl);

registry.loadDescriptors('org.apache.catalina.connector', cl);

这里org.apache.catalina.connector实际上是一个package的路径全名，看下loadDescriptors方法：

Java代码

/** Lookup the component descriptor in the package and
* in the parent packages.
*
* @param packageName
*/
public void loadDescriptors( String packageName, ClassLoader classLoader ) {
String res=packageName.replace( '.', '/');
if( log.isTraceEnabled() ) {
log.trace('Finding descriptor ' res );
}
if( searchedPaths.get( packageName ) != null ) {
return;
}
String descriptors=res '/mbeans-descriptors.ser';
URL dURL=classLoader.getResource( descriptors );
if( dURL == null ) {
descriptors=res '/mbeans-descriptors.xml';
dURL=classLoader.getResource( descriptors );
}
if( dURL == null ) {
return;
}
log.debug( 'Found ' dURL);
searchedPaths.put( packageName, dURL );
try {
if( descriptors.endsWith('.xml' ))
loadDescriptors('MbeansDescriptorsDigesterSource', dURL, null);
else
loadDescriptors('MbeansDescriptorsSerSource', dURL, null);
return;
} catch(Exception ex ) {
log.error('Error loading ' dURL);
}
return;
}

/** Lookup the component descriptor in the package and * in the parent packages. * * @param packageName */ public void loadDescriptors( String packageName, ClassLoader classLoader ) { String res=packageName.replace( '.', '/'); if( log.isTraceEnabled() ) { log.trace('Finding descriptor ' res ); } if( searchedPaths.get( packageName ) != null ) { return; } String descriptors=res '/mbeans-descriptors.ser'; URL dURL=classLoader.getResource( descriptors ); if( dURL == null ) { descriptors=res '/mbeans-descriptors.xml'; dURL=classLoader.getResource( descriptors ); } if( dURL == null ) { return; } log.debug( 'Found ' dURL); searchedPaths.put( packageName, dURL ); try { if( descriptors.endsWith('.xml' )) loadDescriptors('MbeansDescriptorsDigesterSource', dURL, null); else loadDescriptors('MbeansDescriptorsSerSource', dURL, null); return; } catch(Exception ex ) { log.error('Error loading ' dURL); } return; }

第13到15行是先在Registry类的缓存searchedPaths中查找是否已经加载了该package所对应的配置文件，如果没有在第16到18行会在该包路径下面查找是否有mbeans-descriptors.ser文件，没有则在第20到23行查找同路径下的mbeans-descriptors.xml文件。找到之后在第29行放入缓存searchedPaths。我们既然以org.apache.catalina.connector为例，则找到的是该路径下的mbeans-descriptors.xml。所以会接着执行第32行loadDescriptors('MbeansDescriptorsDigesterSource', dURL, null)：

Java代码

private void loadDescriptors(String sourceType, Object source,
String param) throws Exception {
load(sourceType, source, param);
}

private void loadDescriptors(String sourceType, Object source, String param) throws Exception { load(sourceType, source, param); }

这段代码会执行load方法：

Java代码

public List<ObjectName> load( String sourceType, Object source,
String param) throws Exception {
if( log.isTraceEnabled()) {
log.trace('load ' source );
}
String location=null;
String type=null;
Object inputsource=null;
if( source instanceof URL ) {
URL url=(URL)source;
location=url.toString();
type=param;
inputsource=url.openStream();
if( sourceType == null ) {
sourceType = sourceTypeFromExt(location);
}
} else if( source instanceof File ) {
location=((File)source).getAbsolutePath();
inputsource=new FileInputStream((File)source);
type=param;
if( sourceType == null ) {
sourceType = sourceTypeFromExt(location);
}
} else if( source instanceof InputStream ) {
type=param;
inputsource=source;
} else if( source instanceof Class<?> ) {
location=((Class<?>)source).getName();
type=param;
inputsource=source;
if( sourceType== null ) {
sourceType='MbeansDescriptorsIntrospectionSource';
}
}
if( sourceType==null ) {
sourceType='MbeansDescriptorsDigesterSource';
}
ModelerSource ds=getModelerSource(sourceType);
List<ObjectName> mbeans =
ds.loadDescriptors(this, type, inputsource);
return mbeans;
}

public List<ObjectName> load( String sourceType, Object source, String param) throws Exception { if( log.isTraceEnabled()) { log.trace('load ' source ); } String location=null; String type=null; Object inputsource=null; if( source instanceof URL ) { URL url=(URL)source; location=url.toString(); type=param; inputsource=url.openStream(); if( sourceType == null ) { sourceType = sourceTypeFromExt(location); } } else if( source instanceof File ) { location=((File)source).getAbsolutePath(); inputsource=new FileInputStream((File)source); type=param; if( sourceType == null ) { sourceType = sourceTypeFromExt(location); } } else if( source instanceof InputStream ) { type=param; inputsource=source; } else if( source instanceof Class<?> ) { location=((Class<?>)source).getName(); type=param; inputsource=source; if( sourceType== null ) { sourceType='MbeansDescriptorsIntrospectionSource'; } } if( sourceType==null ) { sourceType='MbeansDescriptorsDigesterSource'; } ModelerSource ds=getModelerSource(sourceType); List<ObjectName> mbeans = ds.loadDescriptors(this, type, inputsource); return mbeans; }

第10到35行说穿是是为该方法适配多种数据源类型给inputsource变量赋上一个输入流。第40行会根据sourceType构造一个ModelerSource对象：

Java代码

private ModelerSource getModelerSource( String type )
throws Exception
{
if( type==null ) type='MbeansDescriptorsDigesterSource';
if( type.indexOf( '.') < 0 ) {
type='org.apache.tomcat.util.modeler.modules.' type;
}
Class<?> c = Class.forName(type);
ModelerSource ds=(ModelerSource)c.newInstance();
return ds;
}

private ModelerSource getModelerSource( String type ) throws Exception { if( type==null ) type='MbeansDescriptorsDigesterSource'; if( type.indexOf( '.') < 0 ) { type='org.apache.tomcat.util.modeler.modules.' type; } Class<?> c = Class.forName(type); ModelerSource ds=(ModelerSource)c.newInstance(); return ds; }

上面看到sourceType传入的值是'MbeansDescriptorsDigesterSource'。所以getModelerSource方法最后返回的是org.apache.tomcat.util.modeler.modules.MbeansDescriptorsDigesterSource类的一个实例。

最后执行该ModelerSource对象的loadDescriptors(this, type, inputsource) 方法，因为该方法是一个抽象方法，所以这里实际执行的org.apache.tomcat.util.modeler.modules.MbeansDescriptorsDigesterSource类的loadDescriptors方法：

Java代码

@Override
public List<ObjectName> loadDescriptors( Registry registry, String type,
Object source) throws Exception {
setRegistry(registry);
setType(type);
setSource(source);
execute();
return mbeans;
}

@Override public List<ObjectName> loadDescriptors( Registry registry, String type, Object source) throws Exception { setRegistry(registry); setType(type); setSource(source); execute(); return mbeans; }

前三个set方法毋庸多言，关键是最后的execute方法：

Java代码

public void execute() throws Exception {
if (registry == null) {
registry = Registry.getRegistry(null, null);
}
InputStream stream = (InputStream) source;
if (digester == null) {
digester = createDigester();
}
ArrayList<ManagedBean> loadedMbeans = new ArrayList<ManagedBean>();
synchronized (digester) {
// Process the input file to configure our registry
try {
// Push our registry object onto the stack
digester.push(loadedMbeans);
digester.parse(stream);
} catch (Exception e) {
log.error('Error digesting Registry data', e);
throw e;
} finally {
digester.reset();
}
}
Iterator<ManagedBean> iter = loadedMbeans.iterator();
while (iter.hasNext()) {
registry.addManagedBean(iter.next());
}
}

public void execute() throws Exception { if (registry == null) { registry = Registry.getRegistry(null, null); } InputStream stream = (InputStream) source; if (digester == null) { digester = createDigester(); } ArrayList<ManagedBean> loadedMbeans = new ArrayList<ManagedBean>(); synchronized (digester) { // Process the input file to configure our registry try { // Push our registry object onto the stack digester.push(loadedMbeans); digester.parse(stream); } catch (Exception e) { log.error('Error digesting Registry data', e); throw e; } finally { digester.reset(); } } Iterator<ManagedBean> iter = loadedMbeans.iterator(); while (iter.hasNext()) { registry.addManagedBean(iter.next()); } }}

在第3行又看到了前面提到的Registry.getRegistry(null, null)方法，这里就是获取Registry的静态成员的引用。这段方法作用就是对source进行一次Digester解析，如果还不了解Digester解析，可以看看之前Tomcat源码分析的一篇文章：Tomcat7启动分析（三）Digester的使用。注意第18行digester的顶层对象是loadedMbeans，重点看下第9行createDigester()方法的调用：

Java代码

protected static Digester createDigester() {
Digester digester = new Digester();
digester.setNamespaceAware(false);
digester.setValidating(false);
URL url = Registry.getRegistry(null, null).getClass().getResource
('/org/apache/tomcat/util/modeler/mbeans-descriptors.dtd');
digester.register
('-//Apache Software Foundation//DTD Model MBeans Configuration File',
url.toString());
// Configure the parsing rules
digester.addObjectCreate
('mbeans-descriptors/mbean',
'org.apache.tomcat.util.modeler.ManagedBean');
digester.addSetProperties
('mbeans-descriptors/mbean');
digester.addSetNext
('mbeans-descriptors/mbean',
'add',
'java.lang.Object');
digester.addObjectCreate
('mbeans-descriptors/mbean/attribute',
'org.apache.tomcat.util.modeler.AttributeInfo');
digester.addSetProperties
('mbeans-descriptors/mbean/attribute');
digester.addSetNext
('mbeans-descriptors/mbean/attribute',
'addAttribute',
'org.apache.tomcat.util.modeler.AttributeInfo');
......
return digester;
}

protected static Digester createDigester() { Digester digester = new Digester(); digester.setNamespaceAware(false); digester.setValidating(false); URL url = Registry.getRegistry(null, null).getClass().getResource ('/org/apache/tomcat/util/modeler/mbeans-descriptors.dtd'); digester.register ('-//Apache Software Foundation//DTD Model MBeans Configuration File', url.toString()); // Configure the parsing rules digester.addObjectCreate ('mbeans-descriptors/mbean', 'org.apache.tomcat.util.modeler.ManagedBean'); digester.addSetProperties ('mbeans-descriptors/mbean'); digester.addSetNext ('mbeans-descriptors/mbean', 'add', 'java.lang.Object'); digester.addObjectCreate ('mbeans-descriptors/mbean/attribute', 'org.apache.tomcat.util.modeler.AttributeInfo'); digester.addSetProperties ('mbeans-descriptors/mbean/attribute'); digester.addSetNext ('mbeans-descriptors/mbean/attribute', 'addAttribute', 'org.apache.tomcat.util.modeler.AttributeInfo'); ...... return digester; }

上面这段代码其实很长，但绝大部分都是模板代码，理解几句的含义后面代码都很相似。这就是一个xml文件的解析，第13到15行是值在碰到xml文件的mbeans-descriptors节点的子节点mbean时构造一个org.apache.tomcat.util.modeler.ManagedBean对象，第16到17行是读取该节点属性值填充到ManagedBean对象的pojo属性中，第18到21行以ManagedBean对象为入参调用上一段代码分析提到的loadedMbeans对象的add方法。类似的，第23到31行是指在碰到mbeans-descriptors/mbean/attribute节点时构造org.apache.tomcat.util.modeler.AttributeInfo对象，填充pojo属性，并调用父节点构造的对象（即ManagedBean对象）的addAttribute方法。其它代码类似，不再赘述。

接回到上面MbeansDescriptorsDigesterSource类的execute方法第28到31行，在Digester解析完成之后迭代loadedMbeans对象，并调用registry.addManagedBean方法将这些ManagedBean添加到registry中。这样，一次registry.loadDescriptors('org.apache.catalina.connector', cl)调用就会加载该包路径下相对应的ManagedBean对象到Registry类的成员变量中。

下面的时序图列出从GlobalResourcesLifecycleListener类加载其静态成员变量registry到Registry类加载完相应包所对应的ManagedBean的关键方法调用过程：

2.注册MBean实例

2.1.查找ManagedBean

上面说的是一个ManagedBean的加载过程，但它不是一个MBean，可以把它看作一个描述MBean的配置信息的对象，以前面提到的org.apache.catalina.connector为例，在Tomcat7的默认配置启动后实际上有两个Connector实例，因为在server.xml中配置了两条connector节点：

Xml代码

<Connector port='8080' protocol='HTTP/1.1'
connectionTimeout='20000'
redirectPort='8443' />
<Connector port='8009' protocol='AJP/1.3' redirectPort='8443' />

所对应jconsole中会看到两个相应的MBean对象：

但ManageBean实际只是加载了一次。了解了ManagedBean与MBean的对应关系，接下来看看一个MBean是怎么注册到JVM中的。

看过前面Tomcat启动分析的朋友知道容器各组件在启动过程中会相继调用它们的initInternal()、startInternal()两个方法，还是以上面提到的Connector组件为例，Tomcat启动时解析server.xml文件过程中碰到Connector节点配置会构造org.apache.catalina.connector.Connector对象并调用它的initInternal方法：

Java代码

@Override
protected void initInternal() throws LifecycleException {
super.initInternal();

@Override protected void initInternal() throws LifecycleException { super.initInternal();...

在这个方法的开始会调用它的父类org.apache.catalina.util.LifecycleMBeanBase的initInternal方法：

Java代码

private ObjectName oname = null;
protected MBeanServer mserver = null;
/**
* Sub-classes wishing to perform additional initialization should override
* this method, ensuring that super.initInternal() is the first call in the
* overriding method.
*/
@Override
protected void initInternal() throws LifecycleException {
// If oname is not null then registration has already happened via
// preRegister().
if (oname == null) {
mserver = Registry.getRegistry(null, null).getMBeanServer();
oname = register(this, getObjectNameKeyProperties());
}
}

private ObjectName oname = null; protected MBeanServer mserver = null; /** * Sub-classes wishing to perform additional initialization should override * this method, ensuring that super.initInternal() is the first call in the * overriding method. */ @Override protected void initInternal() throws LifecycleException { // If oname is not null then registration has already happened via // preRegister(). if (oname == null) { mserver = Registry.getRegistry(null, null).getMBeanServer(); oname = register(this, getObjectNameKeyProperties()); } }

先获取MBeanServer的实例，接着调用内部的register方法，将当前对象注册到MBeanServer中，看下register方法：

Java代码

protected final ObjectName register(Object obj,
String objectNameKeyProperties) {
// Construct an object name with the right domain
StringBuilder name = new StringBuilder(getDomain());
name.append(':');
name.append(objectNameKeyProperties);
ObjectName on = null;
try {
on = new ObjectName(name.toString());
Registry.getRegistry(null, null).registerComponent(obj, on, null);
} catch (MalformedObjectNameException e) {
log.warn(sm.getString('lifecycleMBeanBase.registerFail', obj, name),
e);
} catch (Exception e) {
log.warn(sm.getString('lifecycleMBeanBase.registerFail', obj, name),
e);
}
return on;
}

protected final ObjectName register(Object obj, String objectNameKeyProperties) { // Construct an object name with the right domain StringBuilder name = new StringBuilder(getDomain()); name.append(':'); name.append(objectNameKeyProperties); ObjectName on = null; try { on = new ObjectName(name.toString()); Registry.getRegistry(null, null).registerComponent(obj, on, null); } catch (MalformedObjectNameException e) { log.warn(sm.getString('lifecycleMBeanBase.registerFail', obj, name), e); } catch (Exception e) { log.warn(sm.getString('lifecycleMBeanBase.registerFail', obj, name), e); } return on; }

重点是第14行调用Registry类的registerComponent方法来注册：

Java代码

public void registerComponent(Object bean, ObjectName oname, String type)
throws Exception
{
if( log.isDebugEnabled() ) {
log.debug( 'Managed= ' oname);
}
if( bean ==null ) {
log.error('Null component ' oname );
return;
}
try {
if( type==null ) {
type=bean.getClass().getName();
}
ManagedBean managed = findManagedBean(bean.getClass(), type);
// The real mbean is created and registered
DynamicMBean mbean = managed.createMBean(bean);
if( getMBeanServer().isRegistered( oname )) {
if( log.isDebugEnabled()) {
log.debug('Unregistering existing component ' oname );
}
getMBeanServer().unregisterMBean( oname );
}
getMBeanServer().registerMBean( mbean, oname);
} catch( Exception ex) {
log.error('Error registering ' oname, ex );
throw ex;
}
}

public void registerComponent(Object bean, ObjectName oname, String type) throws Exception { if( log.isDebugEnabled() ) { log.debug( 'Managed= ' oname); } if( bean ==null ) { log.error('Null component ' oname ); return; } try { if( type==null ) { type=bean.getClass().getName(); } ManagedBean managed = findManagedBean(bean.getClass(), type); // The real mbean is created and registered DynamicMBean mbean = managed.createMBean(bean); if( getMBeanServer().isRegistered( oname )) { if( log.isDebugEnabled()) { log.debug('Unregistering existing component ' oname ); } getMBeanServer().unregisterMBean( oname ); } getMBeanServer().registerMBean( mbean, oname); } catch( Exception ex) { log.error('Error registering ' oname, ex ); throw ex; } }

在第18行根据当前要注册的对象（即Connector对象）的类型查找ManagedBean，沿着这个方法追会发现依次调用了一堆同名的findManagedBean方法，一直到findManagedBean(String name)：

Java代码

public ManagedBean findManagedBean(String name) {
// XXX Group ?? Use Group Type
ManagedBean mb = descriptors.get(name);
if( mb==null )
mb = descriptorsByClass.get(name);
return mb;
}

public ManagedBean findManagedBean(String name) { // XXX Group ?? Use Group Type ManagedBean mb = descriptors.get(name); if( mb==null ) mb = descriptorsByClass.get(name); return mb; }

这段代码意思是依次从Registry类的静态成员变量descriptors、descriptorsByClass中查找相应ManagedBean。那这两个HashMap是什么时候put值进去的呢？答案就在上一部分分析的最后加载ManagedBean时最终调用Registry类的addManagedBean方法：

Java代码

public void addManagedBean(ManagedBean bean) {
// XXX Use group name
descriptors.put(bean.getName(), bean);
if( bean.getType() != null ) {
descriptorsByClass.put( bean.getType(), bean );
}
}

public void addManagedBean(ManagedBean bean) { // XXX Use group name descriptors.put(bean.getName(), bean); if( bean.getType() != null ) { descriptorsByClass.put( bean.getType(), bean ); } }

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