Question

当我使用URLClassLoader加载类时，以下代码是正确的

        Class c1 = classLoader.loadClass("jjzhu.study.tomcat.servlet.PrimitiveServlet");
        for(Method m: c1.getDeclaredMethods()){
            System.out.println(m.getName());
        }

但是当我这样做时，它会抛出ClassNotFoundException

Class c = classLoader.loadClass(String.format("jjzhu.study.tomcat.servlet.%s",servletName));

为什么呢？完整的功能代码是：

public void process(Request request, Response response) throws ServletException, IOException {
    String uri = request.getUri();
    String servletName = uri.substring(uri.lastIndexOf("/") + 1);
    String path = ServletProcessor1.class.getResource("/").toString();

    URL classUrl;
    URLClassLoader classLoader = null;
    try {

        classUrl = new URL(path+"jjzhu/study/tomcat/servlet");
        System.out.println(path+"jjzhu/study/tomcat/servlet");
        URL[] classUrls = {classUrl};
        classLoader = new URLClassLoader(classUrls);
        // this is ok!
        Class c1 = classLoader.loadClass("jjzhu.study.tomcat.servlet.PrimitiveServlet");
        for(Method m: c1.getDeclaredMethods()){
            System.out.println(m.getName());
        }
        // but this failed
        Class c = classLoader.loadClass(String.format("jjzhu.study.tomcat.servlet.%s",servletName));
        for(Method m: c.getDeclaredMethods()){
            System.out.println(m.getName());
        }
        Servlet servlet = (Servlet)c.newInstance();
        servlet.service(request, response);
    }  catch (ClassNotFoundException e) {
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    } catch (InstantiationException e) {
        e.printStackTrace();
    }
}

例外：

init
destroy
service
getServletConfig
getServletInfo
java.lang.ClassNotFoundException: jjzhu.study.tomcat.servlet.PrimitiveServlet
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at jjzhu.study.tomcat.ex02.pyrmont.ServletProcessor1.process(ServletProcessor1.java:39)
at jjzhu.study.tomcat.ex02.pyrmont.HttpServer1.await(HttpServer1.java:41)
at jjzhu.study.tomcat.ex02.pyrmont.HttpServer1.main(HttpServer1.java:60)

当className按参数传递时，URLClassLoader case ClassNotFoundException

0 个答案: