javassist.util

Class HotSwapper

java.lang.Object

javassist.util.HotSwapper

public class HotSwapper
extends java.lang.Object

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

Field Summary

Fields

Modifier and Type	Field and Description
private static java.lang.String	HOST_NAME
private com.sun.jdi.VirtualMachine	jvm
private java.util.Map	newClassFiles
private com.sun.jdi.request.MethodEntryRequest	request
private Trigger	trigger
private static java.lang.String	TRIGGER_NAME

Constructor Summary

Constructors

Constructor and Description
HotSwapper(int port) Connects to the JVM.
HotSwapper(java.lang.String port) Connects to the JVM.

Method Summary

Modifier and Type	Method and Description
private void	deleteEventRequest(com.sun.jdi.request.EventRequestManager manager, com.sun.jdi.request.MethodEntryRequest request)
private com.sun.jdi.connect.Connector	findConnector(java.lang.String connector)
(package private) void	hotswap()
private static com.sun.jdi.request.MethodEntryRequest	methodEntryRequests(com.sun.jdi.request.EventRequestManager manager, java.lang.String classpattern)
void	reload(java.util.Map classFiles) Reloads a class.
void	reload(java.lang.String className, byte[] classFile) Reloads a class.
private void	reload2(java.util.Map map, java.lang.String msg)
private void	startDaemon()
private com.sun.jdi.ReferenceType	toRefType(java.lang.String className)
(package private) com.sun.jdi.event.EventSet	waitEvent()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

jvm

private com.sun.jdi.VirtualMachine jvm

request

private com.sun.jdi.request.MethodEntryRequest request

newClassFiles

private java.util.Map newClassFiles

trigger

private Trigger trigger

HOST_NAME

private static final java.lang.String HOST_NAME

See Also:

Constant Field Values

TRIGGER_NAME

private static final java.lang.String TRIGGER_NAME

Constructor Detail

HotSwapper

public HotSwapper(int port)
           throws java.io.IOException,
                  com.sun.jdi.connect.IllegalConnectorArgumentsException

Connects to the JVM.

Parameters:

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

Throws:

java.io.IOException

com.sun.jdi.connect.IllegalConnectorArgumentsException

HotSwapper

public HotSwapper(java.lang.String port)
           throws java.io.IOException,
                  com.sun.jdi.connect.IllegalConnectorArgumentsException

Connects to the JVM.

Parameters:

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

Throws:

java.io.IOException

com.sun.jdi.connect.IllegalConnectorArgumentsException

Method Detail

findConnector

private com.sun.jdi.connect.Connector findConnector(java.lang.String connector)
                                             throws java.io.IOException

Throws:

java.io.IOException

methodEntryRequests

private static com.sun.jdi.request.MethodEntryRequest methodEntryRequests(com.sun.jdi.request.EventRequestManager manager,
                                                                          java.lang.String classpattern)

deleteEventRequest

private void deleteEventRequest(com.sun.jdi.request.EventRequestManager manager,
                                com.sun.jdi.request.MethodEntryRequest request)

reload

public void reload(java.lang.String className,
                   byte[] classFile)

Reloads a class.

Parameters:

className - the fully-qualified class name.

classFile - the contents of the class file.

reload

public void reload(java.util.Map classFiles)

Reloads a class.

Parameters:

classFiles - a map between fully-qualified class names and class files. The type of the class names is String and the type of the class files is byte[].

toRefType

private com.sun.jdi.ReferenceType toRefType(java.lang.String className)

reload2

private void reload2(java.util.Map map,
                     java.lang.String msg)

startDaemon

private void startDaemon()

waitEvent

com.sun.jdi.event.EventSet waitEvent()
                              throws java.lang.InterruptedException

Throws:

java.lang.InterruptedException

hotswap

void hotswap()