我已经学会了如何动态地将“.class”文件加载到我的程序中,但如果我在tomcat上运行它,则无效。这是代码:
package testPackage;
public class ModuleEngine {
public static void main(String pth, String name) {
ModuleLoader loader = new ModuleLoader(pth, ClassLoader.getSystemClassLoader());
try {
Class clazz = loader.loadClass(name);
Protocol execute = (Protocol)clazz.newInstance();
execute.run();
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
}
public class ModuleLoader extends ClassLoader {
private String pathtobin;
public ModuleLoader(String pathtobin, ClassLoader parent) {
super(parent);
this.pathtobin = pathtobin;
}
@Override
public Class findClass(String className) throws ClassNotFoundException {
try {
byte b[]= fetchClassFromFS(pathtobin + className + ".class");
return defineClass(null, b, 0, b.length);
} catch (FileNotFoundException ex) {
return super.findClass(className);
} catch (IOException ex) {
return super.findClass(className);
}
}
}
我在ModuleEngine类中运行main方法,其中包含类Protocol的子类的路径。此子类放在不同的包中。因此,当我尝试定义它(defineClass)时,它会尝试加载超类(Protocol),但却无法做到。这是堆栈跟踪:
java.lang.ClassNotFoundException: testPackage.Protocol
at java.lang.ClassLoader.findClass(Unknown Source)
at testPackage.ModuleLoader.findClass(ModuleLoader.java:30)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.lang.ClassLoader.defineClass(Unknown Source)
at testPackage.ModuleLoader.findClass(ModuleLoader.java:28)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at testPackage.ModuleEngine.main(ModuleEngine.java:13)
at testPackage.HtmlPage.doGet(HtmlPage.java:27)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:936)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
答案 0 :(得分:5)
而不是ClassLoader.getSystemClassLoader()
尝试使用ModuleEngine.class.getClassLoader ()
。这将返回知道位于ModuleEngine
类附近的类的类加载器。