Java：InvocationTargetException [英] Java: InvocationTargetException
问题描述
我在Java中动态创建类并尝试调用它们中的方法，但是，有时我会得到 java.lang.reflect.InvocationTargetException 。
I am dynamically creating classes in Java and trying to invoke methods in them, however, sometimes I get a java.lang.reflect.InvocationTargetException.
PageGenerator1.java（动态创建）
import java.io.PrintStream;
import java.util.Map;
public class PageGenerator1 implements DynamicPageGenerator {
public PageGenerator1() {
}
@Override
public void generate(PrintStream out, Map<String,String> params, Session session) {
out.print("<html>\r\n<body>\r\n");
if (session.get("counter") == null) {
session.set("counter", 2);
out.println("<h1>Hi "+params.get("name")+" this is your first visit</h1>");
} else {
out.println("<h1>This is your "+session.get("counter")+" visit</h1>");
session.set("counter", 1+((Integer)session.get("counter")));
}
out.print("\r\n</body>\r\n</html>");
}
}
我试图像这样调用它：
logger.info(
"Attempting to invoke the method " + generateMethod + " with an instance of " + generatedClassName + "with the following parameters:\n" +
"\tparams: " + params + "\n" +
"\tcookieSession: " + cookiesSession
);
generateMethod.invoke(Class.forName(generatedClassName).newInstance(), ps, params, cookiesSession);
这是我得到的日志条目：
and this is the log entry I get:
INFO：尝试调用方法
public void cs236369.webserver.requesthandlers.tsp.PageGenerator1.generate（java.io.PrintStream， java.util.Map，cs236369.webserver.requesthandlers.tsp.Session）
，实例为
cs236369.webserver .requesthandlers.tsp.PageGenerator1
包含以下参数：
params：{name = Amir}
cookieSession：{counter = 5}
我得到的例外没有消息，我没有反思等经验，所以我不确定错误是什么意思。你能帮我解释一下我做错了什么吗？
The exception I'm getting doesn't have a message, and I'm not experienced with reflection, etc. so I'm not sure what the error means. Can you help explain what am I doing wrong?
推荐答案
InovcationTargetException意味着你调用的方法引发了异常。要弄清楚你的方法本身有什么问题，请在try-catch块周围包装invoke方法调用并记录 invocationTargetException.getTargetException（）。
InovcationTargetException means that the method that you invoked threw an exception. To figure out what the problem is with your method itself, wrap the invoke method call around a try-catch block and log invocationTargetException.getTargetException().
我可以在你的generateMethod中看到你可能有错误的几个地方。 Session可以为null，session.getCounter（）被强制转换为Integer - 那里可能有classcastexception。
I can see several places in your generateMethod that you could have errors. Session could be null, session.getCounter() is being cast to Integer -- there could be a classcastexception there.
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