com.sector91.wit.resources.ResourceLoader.java Source code

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Here is the source code for com.sector91.wit.resources.ResourceLoader.java

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// The Web framework with class.

// ~~~~~~~~~~~~~~~~~~~~~~~~~~ //

// Copyright (c) 2013 Adam R. Nelson
//
// Licensed 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.sector91.wit.resources;

import java.io.IOException;
import java.io.InputStream;
import java.util.Objects;
import java.util.concurrent.ExecutionException;

import com.esotericsoftware.minlog.Log;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import com.google.common.util.concurrent.UncheckedExecutionException;

public abstract class ResourceLoader<T> {

    static final String TAG = ResourceLoader.class.getSimpleName();

    final ClassLoader context;
    final String rootPath;
    private final LoadingCache<String, T> cache;

    public ResourceLoader(Class<?> context) {
        this(context, "");
    }

    public ResourceLoader(Class<?> context, String rootPath) {
        this(context.getClassLoader(), rootPath);
    }

    public ResourceLoader(Class<?> context, String rootPath, CacheBuilder<? super String, ? super T> cacheBuilder) {
        this(context.getClassLoader(), rootPath, cacheBuilder);
    }

    public ResourceLoader(ClassLoader context) {
        this(context, "");
    }

    public ResourceLoader(ClassLoader context, String rootPath) {
        this(context, rootPath, CacheBuilder.newBuilder());
    }

    public ResourceLoader(ClassLoader context, String rootPath,
            CacheBuilder<? super String, ? super T> cacheBuilder) {
        Objects.requireNonNull(context, "A ResourceLoader's ClassLoader cannot be null.");
        Objects.requireNonNull(rootPath, "A ResourceLoader's root path cannot be null.");
        this.context = context;
        while (rootPath.endsWith("/"))
            rootPath = rootPath.substring(0, rootPath.length() - 1);
        while (rootPath.startsWith("/"))
            rootPath = rootPath.substring(1);
        this.rootPath = rootPath;
        this.cache = cacheBuilder.build(new ResourceCacheLoader());
        Log.trace(TAG, "Created ResourceLoader for path '" + rootPath + "'.");
    }

    public final T load(String path) throws ResourceNotFoundException {
        if (!path.startsWith("/"))
            path = "/" + path;
        try {
            Log.trace(TAG, "Loading resource '" + path + "', under root path '" + rootPath + "'.");
            return cache.get(path);
        } catch (ExecutionException ex) {
            throw (ResourceNotFoundException) ex.getCause();
        } catch (UncheckedExecutionException ex) {
            throw (RuntimeException) ex.getCause();
        }
    }

    protected abstract T convert(String path, InputStream in) throws IOException;

    class ResourceCacheLoader extends CacheLoader<String, T> {
        @Override
        public T load(String path) throws ResourceNotFoundException {
            final InputStream in = context.getResourceAsStream(rootPath + path);
            if (in == null) {
                final String msg = "Could not find resource '" + rootPath + path + "'.";
                Log.debug(TAG, msg);
                throw new ResourceNotFoundException(msg);
            }
            try {
                Log.trace(TAG, "Successfully loaded resource '" + rootPath + path + "'.");
                return convert(path, in);
            } catch (IOException ex) {
                throw new ResourceNotFoundException("Could not read resource '" + rootPath + path + "'.", ex);
            }
        }
    }
}