JMX with Spring and Annotation (Part 1)

I was working on migrating a standalone server to Spring when I started looking into Spring's JMX support.  And then I found how convienent it is to use Annotation to define MBeans instead of creating MBean interfaces.

First of all, I got rid of the old MBean interface:
ServerMBean.java

package com.my.company.server;

import java.io.IOException;

public interface ServerMBean {

    public String getName() throws IOException;

    public String getVersion() throws IOException;

    public long getChannelCount() throws IOException;

    public void shutdown() throws IOException;

    public void sendMessage(String message) throws IOException;

    public String[] getLoggers() throws IOException;

    public String getLogLevel(String category) throws IOException;

    public void setLogLevel(String category, String level) throws IOException;
}

And rewrite the Server class like:

package com.my.company.server;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;

import org.apache.log4j.Level;
import org.apache.log4j.LogManager;
import org.apache.log4j.Logger;
import org.springframework.jmx.export.annotation.ManagedAttribute;
import org.springframework.jmx.export.annotation.ManagedOperation;
import org.springframework.jmx.export.annotation.ManagedOperationParameter;
import org.springframework.jmx.export.annotation.ManagedOperationParameters;
import org.springframework.jmx.export.annotation.ManagedResource;

@ManagedResource(objectName="ChannelServer:type=Server", description="Server")
public class Server {

protected Logger log = Logger.getLogger(getClass());

private String name;
private String version;
private long uptime;
private int channelCount;

protected Server(String name, String version) {
    this.name = name;
    this.version = version;
}

@ManagedAttribute(description="Server Name")
public String getName() {
    return name;
}

@ManagedAttribute(description="Server Version")
public String getVersion() {
    return version;
}

public long getUpTime() {
return uptime;
}

@ManagedAttribute(description="Channel Count")
public long getChannelCount() throws IOException {
    return this.channelCount;
}

@ManagedOperation(description="Shutdown Server")
public void shutdown() throws IOException {
    stop();
}

@ManagedOperation(description="Send a message")
@ManagedOperationParameters({
    @ManagedOperationParameter(name="msg", description="message")
})
public void sendMessage(String msg) throws IOException {
    //blah blah
}

@ManagedOperation(description="Set log level to the given category")
@ManagedOperationParameters({
    @ManagedOperationParameter(name="category", description="category"),
    @ManagedOperationParameter(name="level", description="log level")
})
public void setLogLevel(String category, String level) throws IOException {
    log.warn("Setting log level " + level + " for " + category);
    Level logLevel = Level.toLevel(level);
    LogManager.getLogger(category).setLevel(logLevel);
}

@ManagedOperation(description="Log level for given category")
@ManagedOperationParameters({
    @ManagedOperationParameter(name="category", description="category")
})
public String getLogLevel(String category) throws IOException {
    return LogManager.getLogger(category).getLevel().toString();
}

@ManagedOperation(description="List of loggers")
public String[] getLoggers() throws IOException {
    Enumeration<?> loggers = LogManager.getCurrentLoggers();
    ArrayList<String> loggerList = new ArrayList<String>();
    while (loggers.hasMoreElements()) {
        Logger logger = (Logger)loggers.nextElement();
        loggerList.add(logger.getName());
    }
    Collections.sort(loggerList);
    return loggerList.toArray(new String[0]);
}

public final void start() {
    log.info("Starting channel server...");
    try {
        //blah blah
        uptime = System.currentTimeMillis();
    } catch (Exception ex) {
        log.fatal("Error starting channel server", ex);
        stop();
    }
}

public final void stop() {
    log.info("Shutting down channel server...");
    try {
        //blah blah
    } catch (Throwable e) {
        log.error("error stopping container", e);
        System.exit(1);
    }
    log.info("Shutdown completed");
    System.exit(0);
}
}

Now let's moving on to Spring configuration. First, define the MBeanExporter:

<bean name="jmxAttributeSource" class="org.springframework.jmx.export.annotation.AnnotationJmxAttributeSource"/>

<bean id="exporter" class="org.springframework.jmx.export.MBeanExporter" lazy-init="false" autowire="no">
<property name="autodetect" value="true"/>
<property name="assembler">
<bean class="org.springframework.jmx.export.assembler.MetadataMBeanInfoAssembler">
<property name="attributeSource" ref="jmxAttributeSource"/>
</bean>
</property>
<property name="namingStrategy">
<bean class="org.springframework.jmx.export.naming.MetadataNamingStrategy">
<property name="attributeSource" ref="jmxAttributeSource"/>
</bean>
</property>
</bean>

An much simpler alternative:

<beans default-autowire="byName"
xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd">
    ...
    <context:mbean-export/>
</beans>

JAXB2 Annotations

It is scary to find out that a dependency of your project is no longer supported and you really need a code update. That's what happened to me when I requested the source code of one dependency and I was told no one can find it.

The dependency I need to update is a JAXB client implementation to connect to liveglobalbid (lgb) - a leading developer of online auction software providing a high quality, real time simultaneous video and audio broadcast of a live auction sale. And surprisingly, I was able to get rid of the dependency along with the JAXB dependencies and use JAXB 2.0 API that comes with Java 5 and above.  Besides that, by using JAXB 2.0 Annotations, the new client implementation is simple and light.

First, a sample xml I'll get from lgb:

<?xml version="1.0" encoding="UTF-8" ?>
<caster xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="http://www.liveglobalbid.com/caster.xsd">
    <pid>25717</pid>
    <mountpoint name="blah blah">
        <source id="9">
            <type>sound</type>
            <remoteid>blah blah</remoteid>
            <average_frame_size>94</average_frame_size>
            <average_frame_rate>3.83</average_frame_rate>
        </source>
    </mountpoint>
</caster>

Basic structure here is:

• Caster is the main object (XmlRootElement), which contains a pid and one or more mountpoint object (XmlElement).
• A mountpoint object has one or more source object (XmlElement)
• A source has type, remoteid, average_frame_size, and average_frame_rate (XmlElement)
• So in total, we'll need 3 object models: Caster, MountPoint (XmlType), and Source (XmlType).
• MountPoint has an attribute called name (XmlAttribute)
• Source has an attribute called id (XmlAttribute)

Source.java

package com.my.company.caster.jaxb2;

import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlType;

/**
 * @author k_wang
 *
 */
@XmlType
public class Source {

    @XmlAttribute
    protected int id;

    @XmlElement
    protected String type;

    @XmlElement
    protected String remoteid;

    @XmlElement
    protected int average_frame_size;

    @XmlElement
    protected double average_frame_rate;

    /**
     * default constructor
     */
    public Source() {
        super();
    }

    /**
     * full constructor
     */
    public Source(int id, String type, String remoteid,
          int average_frame_size, double average_frame_rate) {
        super();
        this.id = id;
        this.type = type;
        this.remoteid = remoteid;
        this.average_frame_size = average_frame_size;
        this.average_frame_rate = average_frame_rate;
    }

    public int getId() {
        return id;
    }

    public String getType() {
        return type;
    }

    public String getRemoteid() {
        return remoteid;
    }

    public int getAverageFrameSize() {
        return average_frame_size;
    }

    public int getAverageFrameRate() {
        return average_frame_rate;
    }
}

MountPoint.java

package com.my.company.caster.jaxb2;

import java.util.ArrayList;
import java.util.List;

import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlType;

/**
 * @author k_wang
 *
 */
@XmlType(name="mountpoint")
public class MountPoint {

    @XmlAttribute
    protected String name;

    @XmlElement
    protected List<Source> source = new ArrayList<Source>();

    public MountPoint() {
        super();
    }

    /**
     * @param name
     * @param source
    */
    public MountPoint(String name, List<Source> source) {
        super();
        this.name = name;
        if(source != null)
            this.source = source;
    }

    public String getName() {
        return name;
    }

    public List<Source> getSource() {
        return source;
    }
}

Caster.java

package com.my.company.caster.jaxb2;

import java.util.ArrayList;
import java.util.List;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;

/**
 * @author k_wang
 *
 */
 @XmlRootElement(name="caster")
public class Caster {

    @XmlElement
    protected long pid;

    @XmlElement
    protected List<MountPoint> mountpoint = new ArrayList<MountPoint>();

    public Caster() {
        super();
    }

    public Caster(long pid, List<MountPoint> mountpoint) {
        super();
        this.pid = pid;
        this.mountpoint = mountpoint;
    }

    public long getPid() {
        return pid;
    }

    public List<MountPoint> getMountpoint() {
        return mountpoint;
    }
}

And to get the Caster model from a URL:

public Caster getCaster(URL url) throws JAXBException {
    Caster caster = null;
    try {
        InputStream in = url.openStream();
        Unmarshaller unmarshaller = JAXBContext.newInstance(Caster.class).createUnmarshaller();
        caster = (Caster) unmarshaller.unmarshal(new StreamSource(in));
        in.close();
    } catch (IOException e) {
        new JAXBException("Unable to parse source input stream: ", e);
    }
    return caster;
}