/**
* The contents of this file are subject to the license and copyright
* detailed in the LICENSE and NOTICE files at the root of the source
* tree and available online at
*
* http://www.dspace.org/license/
*/
package org.dspace.kernel;
import java.lang.management.ManagementFactory;
import java.util.HashMap;
import java.util.Map;
import java.util.UUID;
import org.apache.commons.lang.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import javax.management.*;
/**
* Allows the DSpace kernel to be accessed if desired.
*
* @author Aaron Zeckoski (azeckoski @ gmail.com)
*/
public final class DSpaceKernelManager {
private static Logger log = LoggerFactory.getLogger(DSpaceKernelManager.class);
private static DSpaceKernel defaultKernel = null;
private static Map<String, DSpaceKernel> namedKernelMap = new HashMap<String, DSpaceKernel>();
public static DSpaceKernel getDefaultKernel() {
return defaultKernel;
}
public static void setDefaultKernel(DSpaceKernel kernel) {
defaultKernel = kernel;
}
/**
* A lock on the kernel to handle multiple threads getting the first item.
*/
private Object lock = new Object();
/**
* Get the kernel. This will be a single instance for the JVM, but
* the method will retrieve the same instance regardless of this
* object instance.
*
* @return the DSpace kernel
* @throws IllegalStateException if the kernel is not available
*/
public DSpaceKernel getKernel() {
DSpaceKernel kernel = getKernel(null);
if (kernel == null) {
throw new IllegalStateException("The DSpace kernel is not started yet, please start it before attempting to use it");
}
return kernel;
}
/**
* Get the kernel. This will be a single instance for the JVM, but
* the method will retrieve the same instance regardless of this
* object instance.
*
* @param name this is the name of this kernel instance. If you do
* not know what this is then use null.
* @return the DSpace kernel
* @throws IllegalStateException if the kernel is not available or not running
*/
public DSpaceKernel getKernel(String name) {
// Are we getting a named kernel?
if (!StringUtils.isEmpty(name)) {
String checkedName = checkName(name);
if (namedKernelMap.containsKey(checkedName)) {
return namedKernelMap.get(checkedName);
}
if (defaultKernel != null && checkedName.equals(defaultKernel.getMBeanName())) {
return defaultKernel;
}
synchronized (lock) {
MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
try {
ObjectName kernelName = new ObjectName(checkedName);
DSpaceKernel namedKernel = (DSpaceKernel) mbs.invoke(kernelName, "getManagedBean", null, null);
if ( namedKernel == null || ! namedKernel.isRunning()) {
throw new IllegalStateException("The DSpace kernel is not started yet, please start it before attempting to use it");
}
namedKernelMap.put(checkedName, namedKernel);
return namedKernel;
} catch (InstanceNotFoundException e) {
throw new IllegalStateException(e);
} catch (MBeanException e) {
throw new IllegalStateException(e);
} catch (ReflectionException e) {
throw new IllegalStateException(e);
} catch (MalformedObjectNameException e) {
throw new IllegalStateException(e);
} catch (NullPointerException e) {
throw new IllegalStateException(e);
}
}
}
return defaultKernel;
}
/**
* Static initialized random default Kernel name
*/
private static String defaultKernelName = UUID.randomUUID().toString();
/**
* Ensure that we have a name suitable for an mbean.
* @param name the name for the kernel
* @return a proper mbean name based on the given name
*/
public static String checkName(String name) {
String mbeanName = name;
if (name == null || "".equals(name)) {
mbeanName = DSpaceKernel.MBEAN_PREFIX + defaultKernelName + DSpaceKernel.MBEAN_SUFFIX;
} else {
if (! name.startsWith(DSpaceKernel.MBEAN_PREFIX)) {
mbeanName = DSpaceKernel.MBEAN_PREFIX + name + DSpaceKernel.MBEAN_SUFFIX;
}
}
return mbeanName;
}
/**
* Register a new kernel MBean with the given name or fail
* @param mBeanName the bean name to use
* @param kernel the kernel bean to register
* @throws IllegalStateException if the MBean cannot be registered
*/
public static void registerMBean(String mBeanName, DSpaceKernel kernel) {
String checkedMBeanName = DSpaceKernelManager.checkName(mBeanName);
synchronized (mBeanName) {
MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
try {
ObjectName name = new ObjectName(checkedMBeanName);
if (! mbs.isRegistered(name)) {
// register the MBean
mbs.registerMBean(kernel, name);
log.info("Registered new Kernel MBEAN: " + checkedMBeanName + " ["+kernel+"]");
}
} catch (MalformedObjectNameException e) {
throw new IllegalStateException(e);
} catch (InstanceAlreadyExistsException e) {
throw new IllegalStateException(e);
} catch (MBeanRegistrationException e) {
throw new IllegalStateException(e);
} catch (NotCompliantMBeanException e) {
throw new IllegalStateException(e);
} catch (NullPointerException e) {
throw new IllegalStateException(e);
}
}
}
/**
* Unregister an MBean if possible
* @param mBeanName the bean name to use
* @return true if the MBean was unregistered, false otherwise
*/
public static boolean unregisterMBean(String mBeanName) {
String checkedMBeanName = DSpaceKernelManager.checkName(mBeanName);
synchronized (mBeanName) {
MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
try {
mbs.unregisterMBean(new ObjectName(checkedMBeanName));
return true;
}
catch (InstanceNotFoundException ie) {
//If this exception is thrown, the specified MBean is not currently registered
//So, we'll ignore the error and return true
return true;
}
catch (Exception e) {
//log this issue as a System Warning. Also log the underlying error message.
log.warn("Failed to unregister the MBean: " + checkedMBeanName, e);
return false;
}
}
}
}