java本身建议创建ClassLoader子类，并完成类似addURL方法已达到动态加载类路径。但在第三方包运行时，对方已经实现了ClassLoader子类且未提供此方法。则可以利用JVMPI技术完成这一操作。
java 部分:
<com.myCom.myproj.myclass>
extClassLoader = Thread.currentThread().getContextClassLoader();
File extDir = new File( System.getProperty( "cyanea.home" )+"/lib/ext/" );
File extFiles[] = extDir.listFiles();
ArrayList loaders = null;
if( extFiles != null )
{
for( int i = 0 ; i < extFiles.length ; i ++ )
{
try
{
loaders = addClassPath( extClassLoader, extFiles[i].toURL() );
}catch( Exception e )
{
System.out.println( "exception in addClassPath" );
}
}
C 部分:
#include "classloader.h"
#pragma convlit(resume)
//it is a helper function to get the URL of a loader
//addClassPath will return an arraylist of loader, iterate the arraylist and call this function
//will print out the class loader loading sequence
JNIEXPORT jobject JNICALL Java_com_myCom_myproj_myclass_addClassPath( JNIEnv *env, jobject thisObject, jobject extclassloader, jobject url )
{
jobject loaders = NULL;
try{
if( extclassloader == NULL || url == NULL ) throw 0;
jclass extclassloaderclass = env->GetObjectClass( extclassloader );
//add code to deal with the ClassLoader Implement Class here.
//load
jfieldID ucpid = env->GetFieldID( extclassloaderclass, "ucp", "Lsun/misc/URLClassPath;" );
if( ucpid == NULL ) throw 5;
jobject ucp = env->GetObjectField( extclassloader, ucpid );
if( ucp == NULL ) throw 6;
jclass ucpclass = env->GetObjectClass( ucp );
jfieldID pathid = env->GetFieldID( ucpclass, "path", "Ljava/util/ArrayList;" );
if( pathid == NULL ) throw 7;
jobject path = env->GetObjectField( ucp, pathid );
if( path == NULL ) throw 8;
jclass pathclass = env->GetObjectClass( path );
jmethodID add2path = env->GetMethodID( pathclass, "add", "(ILjava/lang/Object;)V" );
if( add2path == NULL ) throw 9;
env->CallVoidMethod( path, add2path, 0, url );
if( env->ExceptionOccurred() ) throw 10;
jmethodID check = env->GetStaticMethodID( ucpclass, "check", "(Ljava/net/URL;)V" );
if( check == NULL ) throw 11;
env->CallStaticVoidMethod( ucpclass, check, url );
if( env->ExceptionOccurred() ) throw 12;
//create loader and add to loaders and lmap
jfieldID loadersID = env->GetFieldID( ucpclass, "loaders", "Ljava/util/ArrayList;" );
jfieldID lmapID = env->GetFieldID( ucpclass, "lmap", "Ljava/util/HashMap;" );
if( loadersID == NULL || lmapID == NULL ) throw 13;
loaders = env->GetObjectField( ucp, loadersID );
jobject lmap = env->GetObjectField( ucp, lmapID );
if( loaders == NULL || lmap == NULL )
{
throw 14;
}
jfieldID jarHandlerID = env->GetFieldID( ucpclass, "jarHandler", "Ljava/net/URLStreamHandler;" );
if( jarHandlerID == NULL ) throw 15;
jobject jarHandler = env->GetObjectField( ucp, jarHandlerID );
if( jarHandler == NULL ) printf( "jar handler is null" );
jclass jarloaderclass = env->FindClass( "sun/misc/URLClassPath$JarLoader" );
if( jarloaderclass == NULL )
{
throw 16;
}
jmethodID jarloaderconstructor = env->GetMethodID( jarloaderclass, "<init>", "(Ljava/net/URL;Ljava/net/URLStreamHandler;Ljava/util/HashMap;)V" );
if( jarloaderconstructor == NULL ) throw 17;
//create a new instance of JarLoader
jobject jarloader = env->NewObject( jarloaderclass, jarloaderconstructor, url, jarHandler, lmap );
if( jarloader == NULL ) throw 18;
jclass loadersclass = env->GetObjectClass( loaders );
jclass lmapclass = env->GetObjectClass( lmap );
//add jarloader to loaders
jmethodID add2loaders = env->GetMethodID( loadersclass, "add", "(ILjava/lang/Object;)V" );
if( add2loaders == NULL ) throw 19;
env->CallVoidMethod( loaders, add2loaders, 0, jarloader);
if( env->ExceptionOccurred() ) throw 20;
//put (url,jarloader) to lmap
jmethodID put2lmap = env->GetMethodID( lmapclass, "put", "(Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;" );
if( put2lmap == NULL ) throw 21;
env->CallObjectMethod( lmap, put2lmap, url, jarloader );
if( env->ExceptionOccurred() ) throw 22;
}catch( int errcode )
{
loaders = NULL;
probelog( ERROR_LOG , "PROBE_DEBUG", "Error" );
}
return loaders;
}
#pragma convlit(suspend)
