如何加载不在类路径中且在 jar 中的类？

Question

我想加载一个在罐子里的类。我已经尝试使用此代码加载类：URL dirUrl = jarFile.toURL();URLClassLoader ucl = new URLClassLoader(new URL[] {dirUrl}, getClass().getClassLoader());Class<?> clazz = ucl.loadClass(mainClass);ucl.close();我得到一个例外，它找不到课程：java.lang.RuntimeException: java.lang.ClassNotFoundException: net.api.main        at net.al.Main.onEnable(Main.java:39) ~[?:?]        at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:321) ~[spigot.jar:git-Spigot-db6de12-18fbb24]        at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:340) [spigot.jar:git-Spigot-db6de12-18fbb24]        at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:405) [spigot.jar:git-Spigot-db6de12-18fbb24]        at org.bukkit.craftbukkit.v1_8_R3.CraftServer.loadPlugin(CraftServer.java:357) [spigot.jar:git-Spigot-db6de12-18fbb24]        at org.bukkit.craftbukkit.v1_8_R3.CraftServer.enablePlugins(CraftServer.java:317) [spigot.jar:git-Spigot-db6de12-18fbb24]        at org.bukkit.craftbukkit.v1_8_R3.CraftServer.reload(CraftServer.java:741) [spigot.jar:git-Spigot-db6de12-18fbb24]        at org.bukkit.Bukkit.reload(Bukkit.java:535) [spigot.jar:git-Spigot-db6de12-18fbb24]

Answer 1

我通过将 jar 添加到类路径来修复它。文件到 jar 路径的代码：

public static void addURLToClassPath(URL url) throws IllegalAccessException, IllegalArgumentException, InvocationTargetException, NoSuchMethodException, SecurityException

    {

        URLClassLoader classLoader = (URLClassLoader) MyClass.class.getClassLoader();

        @SuppressWarnings("rawtypes")

        Class clazz = URLClassLoader.class;

        @SuppressWarnings("unchecked")

        Method method = clazz.getDeclaredMethod("addURL", new Class[] { URL.class });

        method.setAccessible(true);

        method.invoke(classLoader, new Object[] { url });

    }

Answer 2

请检查net.api.main是否存在

或者检查变量 jarFile 和 mainClass