Package org.hotswap.agent.plugin.hotswapper

Class HotSwapperJpda

  • public class HotSwapperJpda
extends Object
    Example HotSwapperJpda class from javaassist is copied to the plugin, because it needs to reside in the application classloader to avoid NoClassDefFound error on tools.jar classes. Otherwise it is the same code as in javassist.

    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 HotSwapperJpda. Any port number can be specified. Since HotSwapperJpda 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 HotSwapperJpda is easy. See the following example: 

       CtClass clazz = ...
 byte[] classFile = clazz.toBytecode();
 HotSwapperJpda hs = new HotSwapperJpda(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 HotSwapperJpda object so that they can reload a number of classes.

    Since:
    3.1

    • Constructor Detail

      • HotSwapperJpda

        public HotSwapperJpda​(int port)
               throws IOException,
                      com.sun.jdi.connect.IllegalConnectorArgumentsException
        Connects to the JVM.
        Parameters:
        port - the port number used for the connection to the JVM.
        Throws:
        IOException
        com.sun.jdi.connect.IllegalConnectorArgumentsException

      • HotSwapperJpda

        public HotSwapperJpda​(String port)
               throws IOException,
                      com.sun.jdi.connect.IllegalConnectorArgumentsException
        Connects to the JVM.
        Parameters:
        port - the port number used for the connection to the JVM.
        Throws:
        IOException
        com.sun.jdi.connect.IllegalConnectorArgumentsException

    • Method Detail

      • reload

        public void reload​(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​(Map<String,​byte[]> 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[].

      • swapClasses

        public void swapClasses​(Class original,
                        String swap)
                 throws Exception
        Swap class definition from another class file.

        This is mainly useful for unit testing - declare multiple version of a class and then hotswap definition and do the tests.

        Parameters:
        original - original class currently in use
        swap - fully qualified class name of class to swap
        Throws:
        Exception - swap exception