spring-boot-nebula/spring-boot-nebula-common/src/main/java/com/nebula/base/utils/ResourcesUtil.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
package com.nebula.base.utils;

import com.nebula.base.utils.io.IOUtil;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;

/**
 * @author : wh
 * @date : 2023/11/18 14:01
 * @description:
 */
public class ResourcesUtil {
    
    // ---------------------------------------------------------------- get resource
    
    /**
     * Retrieves given resource as URL.
     * @see #getResourceUrl(String, ClassLoader)
     */
    public static URL getResourceUrl(final String resourceName) {
        return getResourceUrl(resourceName, null);
    }
    
    /**
     * Retrieves given resource as URL. Resource is always absolute and may
     * starts with a slash character.
     * <p>
     * Resource will be loaded using class loaders in the following order:
     * <ul>
     * <li>{@link Thread#getContextClassLoader() Thread.currentThread().getContextClassLoader()}</li>
     * <li>{@link Class#getClassLoader() ClassLoaderUtil.class.getClassLoader()}</li>
     * <li>if <code>callingClass</code> is provided: {@link Class#getClassLoader() callingClass.getClassLoader()}</li>
     * </ul>
     */
    public static URL getResourceUrl(String resourceName, final ClassLoader classLoader) {
        
        if (resourceName.startsWith("/")) {
            resourceName = resourceName.substring(1);
        }
        
        URL resourceUrl;
        
        // try #1 - using provided class loader
        if (classLoader != null) {
            resourceUrl = classLoader.getResource(resourceName);
            if (resourceUrl != null) {
                return resourceUrl;
            }
        }
        
        // try #2 - using thread class loader
        final ClassLoader currentThreadClassLoader = Thread.currentThread().getContextClassLoader();
        if ((currentThreadClassLoader != null) && (currentThreadClassLoader != classLoader)) {
            resourceUrl = currentThreadClassLoader.getResource(resourceName);
            if (resourceUrl != null) {
                return resourceUrl;
            }
        }
        
        // try #3 - using caller classloader, similar as Class.forName()
        final Class callerClass = ClassUtil.getCallerClass(2);
        final ClassLoader callerClassLoader = callerClass.getClassLoader();
        
        if ((callerClassLoader != classLoader) && (callerClassLoader != currentThreadClassLoader)) {
            resourceUrl = callerClassLoader.getResource(resourceName);
            if (resourceUrl != null) {
                return resourceUrl;
            }
        }
        
        return null;
    }
    
    // ---------------------------------------------------------------- get resource string
    
    public static String getResourceAsString(final String resourceName) throws IOException {
        final InputStream inputStream = getResourceAsStream(resourceName);
        try {
            final char[] data = IOUtil.readChars(inputStream);
            return new String(data);
        } finally {
            IOUtil.close(inputStream);
        }
    }
    
    // ---------------------------------------------------------------- get resource stream
    
    /**
     * Opens a resource of the specified name for reading.
     * @see #getResourceAsStream(String, ClassLoader)
     */
    public static InputStream getResourceAsStream(final String resourceName) throws IOException {
        return getResourceAsStream(resourceName, null);
    }
    
    /**
     * Opens a resource of the specified name for reading.
     * @see #getResourceUrl(String, ClassLoader)
     */
    public static InputStream getResourceAsStream(final String resourceName, final ClassLoader callingClass) throws IOException {
        final URL url = getResourceUrl(resourceName, callingClass);
        if (url != null) {
            return url.openStream();
        }
        return null;
    }
    
    /**
     * Opens a resource of the specified name for reading. Controls caching,
     * that is important when the same jar is reloaded using custom classloader.
     */
    public static InputStream getResourceAsStream(final String resourceName, final ClassLoader callingClass, final boolean useCache) throws IOException {
        final URL url = getResourceUrl(resourceName, callingClass);
        if (url != null) {
            final URLConnection urlConnection = url.openConnection();
            urlConnection.setUseCaches(useCache);
            return urlConnection.getInputStream();
        }
        return null;
    }
    
}