我在将ServiceLoader集成到我的Android应用中时遇到问题，以集成插件系统。
public class StrategieClassLoader extends URLClassLoader {
private ClassLoader m_SystemClassLoader;
private static Set<String> m_SaveClasses = new HashSet<String>();
{
m_SaveClasses.add( ESpielsteinFarbe.class.getName() );
m_SaveClasses.add( ISpielstein.class.getName() );
m_SaveClasses.add( SpielsteinPosition.class.getName() );
m_SaveClasses.add( ISpielzug.class.getName() );
m_SaveClasses.add( IStrategie.class.getName() );
m_SaveClasses.add( IStrategieFactory.class.getName() );
m_SaveClasses.add( StrategieException.class.getName() );
}
public StrategieClassLoader(URL[] p_Classpath, ClassLoader p_Parent) {
super(p_Classpath, p_Parent);
m_SystemClassLoader = getSystemClassLoader();
}
@Override
protected synchronized Class<?> loadClass(String p_ClassName, boolean p_Resolve)
throws ClassNotFoundException {
Class<?> l_Class = findLoadedClass(p_ClassName);
if (l_Class == null) {
if (isSystemClass(p_ClassName)) {
l_Class = super.loadClass(p_ClassName, p_Resolve);
} else {
try {
l_Class = findClass(p_ClassName);
} catch (ClassNotFoundException e) {
l_Class = super.loadClass(p_ClassName, p_Resolve);
}
}
}
if (p_Resolve) {
resolveClass(l_Class);
}
return l_Class;
}
private boolean isSystemClass(String p_ClassName) {
return ( m_SaveClasses.contains( p_ClassName ) || p_ClassName.startsWith("java.") || p_ClassName.startsWith("javax.") ||
p_ClassName.startsWith("com.sun."));
}
@Override
public URL getResource(String p_ResourceName) {
URL l_ResourceUrl = findResource(p_ResourceName);
if (l_ResourceUrl == null) {
l_ResourceUrl = super.getResource(p_ResourceName);
}
return l_ResourceUrl;
}
@Override
public Enumeration<URL> getResources(String p_ResourceName) throws IOException {
Enumeration<URL> l_LocalUrls = findResources(p_ResourceName);
Enumeration<URL> l_ParentUrls = null;
if (getParent() != null) {
l_ParentUrls = getParent().getResources(p_ResourceName);
}
final List<URL> l_Urls = new ArrayList<URL>();
if (l_LocalUrls != null) {
while (l_LocalUrls.hasMoreElements()) {
l_Urls.add(l_LocalUrls.nextElement());
}
}
if (l_ParentUrls != null) {
while (l_ParentUrls.hasMoreElements()) {
l_Urls.add(l_ParentUrls.nextElement());
}
}
return new Enumeration<URL>() {
Iterator<URL> l_UrlIterator = l_Urls.iterator();
public boolean hasMoreElements() {
return l_UrlIterator.hasNext();
}
public URL nextElement() {
return l_UrlIterator.next();
}
};
}
@Override
public InputStream getResourceAsStream(String p_ResourceName) {
URL l_ResourceUrl = getResource(p_ResourceName);
try {
return l_ResourceUrl != null ? l_ResourceUrl.openStream() : null;
} catch (IOException e) {
}
return null;
}
}
public static List<IStrategieFactory> load(String p_path)
{
List<IStrategieFactory> l_Facs = new ArrayList<IStrategieFactory>();
File l_PluginDir = new File(p_path);
for( File dir: l_PluginDir.listFiles() )
{
if( dir.isDirectory() )
{
File[] l_Jars = dir.listFiles( new FilenameFilter() {
@Override
public boolean accept(File file, String name) {
// TODO Auto-generated method stub
return name.endsWith( ".jar" );
}
});
List<URL> l_Urls = new ArrayList<URL>();
for( File jar: l_Jars )
{
try {
l_Urls.add( jar.toURI().toURL() );
} catch (MalformedURLException ex) {
ex.printStackTrace();
}
}
if( !l_Urls.isEmpty() )
{
StrategieClassLoader l_ClassLoader = new StrategieClassLoader(l_Urls.toArray( new URL[ l_Urls.size() ]), Thread.currentThread().getContextClassLoader() );
ServiceLoader<IStrategieFactory> loader = ServiceLoader.load(IStrategieFactory.class, l_ClassLoader);
for( IStrategieFactory fac : loader )
{
l_Facs.add( fac );
}
}
}
}
m_Factories = l_Facs;
return m_Factories;
}
}
从externalStorage上的assets文件夹复制的.jar文件，Class可以访问所有文件但运行后崩溃
ServiceLoader<IStrategieFactory> loader = ServiceLoader.load(IStrategieFactory.class, l_ClassLoader);
13967-13967/dievierlustigen5.dhbw.de.a4wins E/AndroidRuntime: FATAL EXCEPTION: main
Process: dievierlustigen5.dhbw.de.a4wins, PID: 13967
java.util.ServiceConfigurationError: Couldn't instantiate class de.dhbw.fourwins.strategy.EasyStratFactory
at java.util.ServiceLoader$ServiceIterator.next(ServiceLoader.java:216)
at dievierlustigen5.dhbw.de.a4wins.strategy.StrategyLoader.load(StrategyLoader.java:78)
at dievierlustigen5.dhbw.de.a4wins.DifficultyActivity.onCreate(DifficultyActivity.java:43)
at android.app.Activity.performCreate(Activity.java:6877)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1136)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3208)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3351)
at android.app.ActivityThread.access$1100(ActivityThread.java:222)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1796)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7230)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.net.URL.getProtocol()' on a null object reference
at java.net.URLClassLoader.getPermissions(URLClassLoader.java:614)
at java.security.SecureClassLoader.getPD(SecureClassLoader.java:140)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:93)
at java.net.URLClassLoader.access$600(URLClassLoader.java:55)
at java.net.URLClassLoader$URLJarHandler.createClass(URLClassLoader.java:364)
at java.net.URLClassLoader$URLJarHandler.findClass(URLClassLoader.java:303)
at java.net.URLClassLoader.findClass(URLClassLoader.java:748)
at dievierlustigen5.dhbw.de.a4wins.strategy.StrategieClassLoader.loadClass(StrategieClassLoader.java:56)
at java.lang.ClassLoader.loadClass(ClassLoader.java:469)
at java.util.ServiceLoader$ServiceIterator.next(ServiceLoader.java:214)
at dievierlustigen5.dhbw.de.a4wins.strategy.StrategyLoader.load(StrategyLoader.java:78)
at dievierlustigen5.dhbw.de.a4wins.DifficultyActivity.onCreate(DifficultyActivity.java:43)
at android.app.Activity.performCreate(Activity.java:6877)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1136)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3208)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3351)
at android.app.ActivityThread.access$1100(ActivityThread.java:222)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1796)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7230)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
也许有人知道如何解决错误？
答案 0 :(得分：0)
在Android运行时期间无法加载正常的.class文件，因为 Android使用另一个VM，它只能读取.dex文件。
所以我必须使用DexClassLoader