Class HotSwapper
- java.lang.Object
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- javassist.util.HotSwapper
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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. SinceHotSwapper
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 theTest
class and load a new version of theTest
class.classFile
is a byte array containing the new contents of the class file for theTest
class. The developers can repatedly callreload()
on the sameHotSwapper
object so that they can reload a number of classes.HotSwap
depends on the debug agent to perform hot-swapping but it is reported that the debug agent is buggy under massively multithreaded environments. If you encounter a problem, tryHotSwapAgent
.- Since:
- 3.1
- See Also:
HotSwapAgent
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Constructor Summary
Constructors Constructor Description HotSwapper(int port)
Connects to the JVM.HotSwapper(java.lang.String port)
Connects to the JVM.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
reload(java.lang.String className, byte[] classFile)
Reloads a class.void
reload(java.util.Map<java.lang.String,byte[]> classFiles)
Reloads a class.
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Constructor Detail
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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
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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
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Method Detail
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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.
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reload
public void reload(java.util.Map<java.lang.String,byte[]> classFiles)
Reloads a class.- Parameters:
classFiles
- a map between fully-qualified class names and class files. The type of the class names isString
and the type of the class files isbyte[]
.
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