一、前言

关于spark包(spark-master)的spark.utils.ClassUtils类工具类对类转换、类加载器、类的实例化加载等进行操作，详情见源码说明。

二、源码说明

package spark.utils;import java.lang.reflect.Array;import java.util.Arrays;import java.util.HashMap;import java.util.HashSet;import java.util.Map;import java.util.Set; public abstract class ClassUtils {        public static final String ARRAY_SUFFIX = "[]";         private static final String INTERNAL_ARRAY_PREFIX = "[";        private static final String NON_PRIMITIVE_ARRAY_PREFIX = "[L";         private static final Map<Class<?>, Class<?>> primitiveWrapperTypeMap = new HashMap<>(8);        private static final Map<Class<?>, Class<?>> primitiveTypeToWrapperMap = new HashMap<>(8);       private static final Map<String, Class<?>> primitiveTypeNameMap = new HashMap<>(32);        private static final Map<String, Class<?>> commonClassCache = new HashMap<>(32);    static {        primitiveWrapperTypeMap.put(Boolean.class, boolean.class);        primitiveWrapperTypeMap.put(Byte.class, byte.class);        primitiveWrapperTypeMap.put(Character.class, char.class);        primitiveWrapperTypeMap.put(Double.class, double.class);        primitiveWrapperTypeMap.put(Float.class, float.class);        primitiveWrapperTypeMap.put(Integer.class, int.class);        primitiveWrapperTypeMap.put(Long.class, long.class);        primitiveWrapperTypeMap.put(Short.class, short.class);        for (Map.Entry<Class<?>, Class<?>> entry : primitiveWrapperTypeMap.entrySet()) {            primitiveTypeToWrapperMap.put(entry.getValue(), entry.getKey());            registerCommonClasses(entry.getKey());        }        Set<Class<?>> primitiveTypes = new HashSet<>(32);        primitiveTypes.addAll(primitiveWrapperTypeMap.values());        primitiveTypes.addAll(Arrays.asList(new Class<?>[] {                boolean[].class, byte[].class, char[].class, double[].class,                float[].class, int[].class, long[].class, short[].class}));        primitiveTypes.add(void.class);        for (Class<?> primitiveType : primitiveTypes) {            primitiveTypeNameMap.put(primitiveType.getName(), primitiveType);        }        registerCommonClasses(Boolean[].class, Byte[].class, Character[].class, Double[].class,                              Float[].class, Integer[].class, Long[].class, Short[].class);        registerCommonClasses(Number.class, Number[].class, String.class, String[].class,                              Object.class, Object[].class, Class.class, Class[].class);        registerCommonClasses(Throwable.class, Exception.class, RuntimeException.class,                              Error.class, StackTraceElement.class, StackTraceElement[].class);    }        private static void registerCommonClasses(Class<?>... commonClasses) {        for (Class<?> clazz : commonClasses) {            commonClassCache.put(clazz.getName(), clazz);        }    }         public static ClassLoader getDefaultClassLoader() {        ClassLoader cl = null;        try {            cl = Thread.currentThread().getContextClassLoader();        } catch (Throwable ex) {            // Cannot access thread context ClassLoader - falling back to system class loader...        }        if (cl == null) {            // No thread context class loader -> use class loader of this class.            cl = ClassUtils.class.getClassLoader();        }        return cl;    }         public static Class<?> forName(String name, ClassLoader classLoader) throws ClassNotFoundException, LinkageError {        Assert.notNull(name, "Name must not be null");        Class<?> clazz = resolvePrimitiveClassName(name);        if (clazz == null) {            clazz = commonClassCache.get(name);        }        if (clazz != null) {            return clazz;        }        // "java.lang.String[]" style arrays        if (name.endsWith(ARRAY_SUFFIX)) {            String elementClassName = name.substring(0, name.length() - ARRAY_SUFFIX.length());            Class<?> elementClass = forName(elementClassName, classLoader);            return Array.newInstance(elementClass, 0).getClass();        }        // "[Ljava.lang.String;" style arrays        if (name.startsWith(NON_PRIMITIVE_ARRAY_PREFIX) && name.endsWith(";")) {            String elementName = name.substring(NON_PRIMITIVE_ARRAY_PREFIX.length(), name.length() - 1);            Class<?> elementClass = forName(elementName, classLoader);            return Array.newInstance(elementClass, 0).getClass();        }        // "[[I" or "[[Ljava.lang.String;" style arrays        if (name.startsWith(INTERNAL_ARRAY_PREFIX)) {            String elementName = name.substring(INTERNAL_ARRAY_PREFIX.length());            Class<?> elementClass = forName(elementName, classLoader);            return Array.newInstance(elementClass, 0).getClass();        }        ClassLoader classLoaderToUse = classLoader;        if (classLoaderToUse == null) {            classLoaderToUse = getDefaultClassLoader();        }        try {            return classLoaderToUse.loadClass(name);        } catch (ClassNotFoundException ex) {            int lastDotIndex = name.lastIndexOf('.');            if (lastDotIndex != -1) {                String innerClassName = name.substring(0, lastDotIndex) + '$' + name.substring(lastDotIndex + 1);                try {                    return classLoaderToUse.loadClass(innerClassName);                } catch (ClassNotFoundException ex2) {                    // swallow - let original exception get through                }            }            throw ex;        }    }         public static Class<?> resolvePrimitiveClassName(String name) {        Class<?> result = null;        // Most class names will be quite long, considering that they        // SHOULD sit in a package, so a length check is worthwhile.        if (name != null && name.length() <= 8) {            // Could be a primitive - likely.            result = primitiveTypeNameMap.get(name);        }        return result;    }     public static String classPackageAsResourcePath(Class<?> clazz) {        if (clazz == null) {            return "";        }        String className = clazz.getName();        int packageEndIndex = className.lastIndexOf('.');        if (packageEndIndex == -1) {            return "";        }        String packageName = className.substring(0, packageEndIndex);        return packageName.replace('.', '/');    }}