ClassUtils.java

package com.hwlcn.security.util;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.InputStream;
import java.lang.*;
import java.lang.reflect.Constructor;


public class ClassUtils {


    private static final Logger log = LoggerFactory.getLogger(ClassUtils.class);

    private static final ClassLoaderAccessor THREAD_CL_ACCESSOR = new ExceptionIgnoringAccessor() {
        @Override
        protected ClassLoader doGetClassLoader() throws Throwable {
            return Thread.currentThread().getContextClassLoader();
        }
    };

    private static final ClassLoaderAccessor CLASS_CL_ACCESSOR = new ExceptionIgnoringAccessor() {
        @Override
        protected ClassLoader doGetClassLoader() throws Throwable {
            return ClassUtils.class.getClassLoader();
        }
    };

    private static final ClassLoaderAccessor SYSTEM_CL_ACCESSOR = new ExceptionIgnoringAccessor() {
        @Override
        protected ClassLoader doGetClassLoader() throws Throwable {
            return ClassLoader.getSystemClassLoader();
        }
    };

    public static InputStream getResourceAsStream(String name) {

        InputStream is = THREAD_CL_ACCESSOR.getResourceStream(name);

        if (is == null) {
            if (log.isTraceEnabled()) {
                log.trace("Resource [" + name + "] was not found via the thread context ClassLoader.  Trying the " +
                        "current ClassLoader...");
            }
            is = CLASS_CL_ACCESSOR.getResourceStream(name);
        }

        if (is == null) {
            if (log.isTraceEnabled()) {
                log.trace("Resource [" + name + "] was not found via the current class loader.  Trying the " +
                        "system/application ClassLoader...");
            }
            is = SYSTEM_CL_ACCESSOR.getResourceStream(name);
        }

        if (is == null && log.isTraceEnabled()) {
            log.trace("Resource [" + name + "] was not found via the thread context, current, or " +
                    "system/application ClassLoaders.  All heuristics have been exhausted.  Returning null.");
        }

        return is;
    }

    public static Class forName(String fqcn) throws UnknownClassException {

        Class clazz = THREAD_CL_ACCESSOR.loadClass(fqcn);

        if (clazz == null) {
            if (log.isTraceEnabled()) {
                log.trace("Unable to load class named [" + fqcn +
                        "] from the thread context ClassLoader.  Trying the current ClassLoader...");
            }
            clazz = CLASS_CL_ACCESSOR.loadClass(fqcn);
        }

        if (clazz == null) {
            if (log.isTraceEnabled()) {
                log.trace("Unable to load class named [" + fqcn + "] from the current ClassLoader.  " +
                        "Trying the system/application ClassLoader...");
            }
            clazz = SYSTEM_CL_ACCESSOR.loadClass(fqcn);
        }

        if (clazz == null) {
            String msg = "Unable to load class named [" + fqcn + "] from the thread context, current, or " +
                    "system/application ClassLoaders.  All heuristics have been exhausted.  Class could not be found.";
            throw new UnknownClassException(msg);
        }

        return clazz;
    }

    public static boolean isAvailable(String fullyQualifiedClassName) {
        try {
            forName(fullyQualifiedClassName);
            return true;
        } catch (UnknownClassException e) {
            return false;
        }
    }

    public static Object newInstance(String fqcn) {
        return newInstance(forName(fqcn));
    }

    public static Object newInstance(String fqcn, Object... args) {
        return newInstance(forName(fqcn), args);
    }

    public static Object newInstance(Class clazz) {
        if (clazz == null) {
            String msg = "Class method parameter cannot be null.";
            throw new IllegalArgumentException(msg);
        }
        try {
            return clazz.newInstance();
        } catch (Exception e) {
            throw new InstantiationException("Unable to instantiate class [" + clazz.getName() + "]", e);
        }
    }

    public static Object newInstance(Class clazz, Object... args) {
        Class[] argTypes = new Class[args.length];
        for (int i = 0; i < args.length; i++) {
            argTypes[i] = args[i].getClass();
        }
        Constructor ctor = getConstructor(clazz, argTypes);
        return instantiate(ctor, args);
    }

    public static Constructor getConstructor(Class clazz, Class... argTypes) {
        try {
            return clazz.getConstructor(argTypes);       //获取匹配参数的 构造函数
        } catch (NoSuchMethodException e) {
            throw new IllegalStateException(e);
        }

    }

    public static Object instantiate(Constructor ctor, Object... args) {
        try {
            return ctor.newInstance(args);
        } catch (Exception e) {
            String msg = "Unable to instantiate Permission instance with constructor [" + ctor + "]";
            throw new InstantiationException(msg, e);
        }
    }


    private static interface ClassLoaderAccessor {
        Class loadClass(String fqcn);
        InputStream getResourceStream(String name);
    }


    private static abstract class ExceptionIgnoringAccessor implements ClassLoaderAccessor {

        public Class loadClass(String fqcn) {
            Class clazz = null;
            ClassLoader cl = getClassLoader();
            if (cl != null) {
                try {
                    clazz = cl.loadClass(fqcn);
                } catch (ClassNotFoundException e) {
                    if (log.isTraceEnabled()) {
                        log.trace("Unable to load clazz named [" + fqcn + "] from class loader [" + cl + "]");
                    }
                }
            }
            return clazz;
        }

        public InputStream getResourceStream(String name) {
            InputStream is = null;
            ClassLoader cl = getClassLoader();
            if (cl != null) {
                is = cl.getResourceAsStream(name);
            }
            return is;
        }

        protected final ClassLoader getClassLoader() {
            try {
                return doGetClassLoader();
            } catch (Throwable t) {
                if (log.isDebugEnabled()) {
                    log.debug("Unable to acquire ClassLoader.", t);
                }
            }
            return null;
        }

        protected abstract ClassLoader doGetClassLoader() throws Throwable;
    }
}