javassist.util: public class: HotSwapper

javassist.util
public class: HotSwapper [javadoc | source]

java.lang.Object
   javassist.util.HotSwapper

A utility class for dynamically reloading a class by the Java Platform Debugger Architecture (JPDA), or HotSwap. It works only with JDK 1.4 and later.

Note: The new definition of the reloaded class must declare the same set of methods and fields as the original definition. The schema change between the original and new definitions is not allowed by the JPDA.

To use this class, the JVM must be launched with the following command line options:

For Java 1.4,

java -Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=8000

For Java 5,

java -agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=8000

Note that 8000 is the port number used by HotSwapper. Any port number can be specified. Since HotSwapper does not launch another JVM for running a target application, this port number is used only for inter-thread communication.

Furthermore, JAVA_HOME/lib/tools.jar must be included in the class path.

Using HotSwapper is easy. See the following example:

CtClass clazz = ...
byte[] classFile = clazz.toBytecode();
HotSwapper hs = new HostSwapper(8000);  // 8000 is a port number.
hs.reload("Test", classFile);

reload() first unload the Test class and load a new version of the Test class. classFile is a byte array containing the new contents of the class file for the Test class. The developers can repatedly call reload() on the same HotSwapper object so that they can reload a number of classes.

since: 3.1 -

Constructor:

Constructor:
public HotSwapper(int port) throws IOException, IllegalConnectorArgumentsException { this(Integer.toString(port)); } Connects to the JVM. Parameters: `port` - the port number used for the connection to the JVM.
public HotSwapper(String port) throws IOException, IllegalConnectorArgumentsException { jvm = null; request = null; newClassFiles = null; trigger = new Trigger(); AttachingConnector connector = (AttachingConnector)findConnector("com.sun.jdi.SocketAttach"); Map arguments = connector.defaultArguments(); ((Connector.Argument)arguments.get("hostname")).setValue(HOST_NAME); ((Connector.Argument)arguments.get("port")).setValue(port); jvm = connector.attach(arguments); EventRequestManager manager = jvm.eventRequestManager(); request = methodEntryRequests(manager, TRIGGER_NAME); } Connects to the JVM. Parameters: `port` - the port number used for the connection to the JVM.

 public HotSwapper(int port) throws IOException, IllegalConnectorArgumentsException {
        this(Integer.toString(port));
}

Connects to the JVM.

Parameters:

port - the port number used for the connection to the JVM.

 public HotSwapper(String port) throws IOException, IllegalConnectorArgumentsException {
        jvm = null;
        request = null;
        newClassFiles = null;
        trigger = new Trigger();
        AttachingConnector connector
            = (AttachingConnector)findConnector("com.sun.jdi.SocketAttach");
        Map arguments = connector.defaultArguments();
        ((Connector.Argument)arguments.get("hostname")).setValue(HOST_NAME);
        ((Connector.Argument)arguments.get("port")).setValue(port);
        jvm = connector.attach(arguments);
        EventRequestManager manager = jvm.eventRequestManager();
        request = methodEntryRequests(manager, TRIGGER_NAME);
}

Connects to the JVM.

Parameters:

port - the port number used for the connection to the JVM.

Method from javassist.util.HotSwapper Summary:
hotswap, reload, reload, waitEvent

Methods from java.lang.Object:
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method from javassist.util.HotSwapper Detail:
void hotswap() { Map map = newClassFiles; jvm.redefineClasses(map); newClassFiles = null; }
public void reload(Map classFiles) { Set set = classFiles.entrySet(); Iterator it = set.iterator(); Map map = new HashMap(); String className = null; while (it.hasNext()) { Map.Entry e = (Map.Entry)it.next(); className = (String)e.getKey(); map.put(toRefType(className), e.getValue()); } if (className != null) reload2(map, className + " etc."); } Reloads a class.
public void reload(String className, byte[] classFile) { ReferenceType classtype = toRefType(className); Map map = new HashMap(); map.put(classtype, classFile); reload2(map, className); } Reloads a class.
EventSet waitEvent() throws InterruptedException { EventQueue queue = jvm.eventQueue(); return queue.remove(); }