Add resource handling utility class

Add ResourceUtils, a class that provides utility methods
for dealing with Java resources on the classpath.

Change-Id: Ie4df249315ad145aabdfb35bb827ffbf6d79e095
Issue-ID: POLICY-922
Signed-off-by: liamfallon <liam.fallon@ericsson.com>

1 files changed, 214 insertions, 0 deletions

diff --git a/utils/src/main/java/org/onap/policy/common/utils/resources/ResourceUtils.java b/utils/src/main/java/org/onap/policy/common/utils/resources/ResourceUtils.java
new file mode 100644
index 00000000..cca6e626
--- /dev/null
+++ b/utils/src/main/java/org/onap/policy/common/utils/resources/ResourceUtils.java
@@ -0,0 +1,214 @@
+/*-
+ * ============LICENSE_START=======================================================
+ *  Copyright (C) 2018 Ericsson. All rights reserved.
+ * ================================================================================
+ * 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.
+ * 
+ * SPDX-License-Identifier: Apache-2.0
+ * ============LICENSE_END=========================================================
+ */
+
+package org.onap.policy.common.utils.resources;
+
+import java.io.ByteArrayOutputStream;
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
+import java.net.URL;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * This is common utility class with static methods for handling Java resources on the class path. It is an abstract
+ * class to prevent any direct instantiation and private constructor to prevent extending this class.
+ */
+public abstract class ResourceUtils {
+    // Get a reference to the logger
+    private static final Logger LOGGER = LoggerFactory.getLogger(ResourceUtils.class);
+
+    // The length of byte buffers used to read resources into strings
+    private static final int BYTE_BUFFER_LENGH = 1024;
+
+    /**
+     * Private constructor used to prevent sub class instantiation.
+     */
+    private ResourceUtils() {
+        // Prevent construction of this class
+    }
+
+    /**
+     * Method to resolve a resource; the local file system is checked first and then the class path is checked.
+     *
+     * @param resourceName The resource name
+     * @return A URL to a resource
+     */
+    public static URL getUrl4Resource(final String resourceName) {
+        // Check the local fine system first
+        final URL urlToResource = getLocalFile(resourceName);
+
+        // Check if this is a local file
+        if (urlToResource != null) {
+            return urlToResource;
+        } else {
+            // Resort to the class path
+            return getUrlResource(resourceName);
+        }
+    }
+
+    /**
+     * Method to return a resource as a string. The resource can be on the local file system or in the class path. The
+     * resource is resolved and loaded into a string.
+     *
+     * @param resourceName The resource name
+     * @return A string containing the resource
+     */
+    public static String getResourceAsString(final String resourceName) {
+        // Get the resource as a stream, we'll convert it to a string then
+        final InputStream resourceStream = getResourceAsStream(resourceName);
+        if (resourceStream == null) {
+            return null;
+        }
+
+        // Read the stream contents in to an output stream
+        final ByteArrayOutputStream resourceOutputStreamBuffer = new ByteArrayOutputStream();
+        final byte[] resourceBuffer = new byte[BYTE_BUFFER_LENGH];
+        int length;
+        try {
+            while ((length = resourceStream.read(resourceBuffer)) != -1) {
+                resourceOutputStreamBuffer.write(resourceBuffer, 0, length);
+            }
+        } catch (final IOException e) {
+            LOGGER.debug("error reading resource stream \"{}\" : " + e.getMessage(), resourceName, e);
+            return null;
+        }
+
+        return resourceOutputStreamBuffer.toString();
+    }
+
+    /**
+     * Method to return a resource as a stream. The resource can be on the local file system or in the class path. The
+     * resource is resolved and returned as a stream.
+     *
+     * @param resourceName The resource name
+     * @return A stream attached to the resource
+     */
+    public static InputStream getResourceAsStream(final String resourceName) {
+        // Find a URL to the resource first
+        final URL urlToResource = getUrl4Resource(resourceName);
+
+        // Check if the resource exists
+        if (urlToResource == null) {
+            // No resource found
+            LOGGER.debug("cound not find resource \"{}\" : ", resourceName);
+            return null;
+        }
+
+        // Read the resource into a string
+        try {
+            return urlToResource.openStream();
+        } catch (final IOException e) {
+            // Any of many IO exceptions such as the resource is a directory
+            LOGGER.debug("error attaching resource \"{}\" to stream : " + e.getMessage(), resourceName, e);
+            return null;
+        }
+    }
+
+    /**
+     * Method to get a URL resource from the class path.
+     *
+     * @param resourceName The resource name
+     * @return The URL to the resource
+     */
+    public static URL getUrlResource(final String resourceName) {
+        try {
+            final ClassLoader classLoader = ResourceUtils.class.getClassLoader();
+
+            final String[] fileParts = resourceName.split("/");
+            // Read the resource
+            URL url = classLoader.getResource(resourceName);
+
+            // Check if the resource is defined
+            if (url != null) {
+                // Return the resource as a file name
+                LOGGER.debug("found URL resource \"{}\" : ", url);
+                return url;
+            } else {
+                url = classLoader.getResource(fileParts[fileParts.length - 1]);
+                if (url == null) {
+                    LOGGER.debug("cound not find URL resource \"{}\" : ", resourceName);
+                    return null;
+                }
+                LOGGER.debug("found URL resource \"{}\" : ", url);
+                return url;
+            }
+        } catch (final Exception e) {
+            LOGGER.debug("error getting URL resource \"{}\" : " + e.getMessage(), e);
+            return null;
+        }
+    }
+
+    /**
+     * Method to get a URL resource from the local machine.
+     *
+     * @param resourceName The resource name
+     * @return The URL to the resource
+     */
+    public static URL getLocalFile(final String resourceName) {
+        try {
+            // Input might already be in URL format
+            final URL ret = new URL(resourceName);
+            final File f = new File(ret.toURI());
+            if (f.exists()) {
+                return ret;
+            }
+        } catch (final Exception ignore) {
+            // We ignore exceptions here and catch them below
+        }
+
+        try {
+            final File f = new File(resourceName);
+            // Check if the file exists
+            if (f.exists()) {
+                final URL urlret = f.toURI().toURL();
+                LOGGER.debug("resource \"{}\" was found on the local file system", f.toURI().toURL());
+                return urlret;
+            } else {
+                LOGGER.debug("resource \"{}\" does not exist on the local file system", resourceName);
+                return null;
+            }
+        } catch (final Exception e) {
+            LOGGER.debug("error finding resource \"{}\" : " + e.getMessage(), e);
+            return null;
+        }
+    }
+
+    /**
+     * Gets the file path for a resource on the local file system or on the class path.
+     *
+     * @param resource the resource to the get the file path for
+     * @return the resource file path
+     */
+    public static String getFilePath4Resource(final String resource) {
+        if (resource == null) {
+            return null;
+        }
+
+        URL modelFileUrl = getUrl4Resource(resource);
+        if (modelFileUrl != null) {
+            return modelFileUrl.getPath();
+        } else {
+            return resource;
+        }
+    }
+}