Configuration: environment variable expansion

Enable environment variable expansion in crail-site.conf.

Close #7

Signed-off-by: Jonas Pfefferle <pepperjo@apache.org>

client/src/main/java/org/apache/crail/conf/CrailConfiguration.java

@@ -19,36 +19,80 @@
 
 package org.apache.crail.conf;
 
+import org.apache.crail.utils.CrailUtils;
+import org.slf4j.Logger;
+
 import java.io.File;
 import java.io.FileInputStream;
 import java.io.IOException;
 import java.util.Properties;
 import java.util.concurrent.ConcurrentHashMap;
-
-import org.apache.crail.utils.CrailUtils;
-import org.slf4j.Logger;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 public class CrailConfiguration {
 	private static final Logger LOG = CrailUtils.getLogger();
 	private ConcurrentHashMap<String, String> conf;
-
-
-	public CrailConfiguration() throws IOException{
+
+	public CrailConfiguration() throws IOException {
 		conf = new ConcurrentHashMap<>();
 		Properties properties = loadProperties("crail-site.conf");
 		mergeProperties(properties);
 	}
 
+	private static String expandEnvVars(String input) throws IOException {
+		if (null == input) {
+			return null;
+		}
+		// match ${ENV_VAR_NAME} or $ENV_VAR_NAME
+		Pattern p = Pattern.compile("\\$\\{(\\w+)\\}|\\$(\\w+)");
+		Matcher m = p.matcher(input);
+		StringBuffer output = new StringBuffer();
+		while (m.find()) {
+			String envVar;
+			if (m.group(1) != null) {
+				envVar = m.group(1);
+			} else {
+				envVar = m.group(2);
+			}
+			String envVal = System.getenv(envVar);
+			if (envVal == null) {
+				throw new IOException("Could not expand environment variable $" + envVar);
+			}
+			m.appendReplacement(output, envVal);
+		}
+		m.appendTail(output);
+		return output.toString();
+	}
+
+	private static Properties loadProperties(String resourceName) throws IOException {
+		Properties properties = new Properties();
+
+		String base = System.getenv("CRAIL_HOME");
+		FileInputStream inputStream = new FileInputStream(new File(base + "/conf/" + resourceName));
+
+		try {
+			properties.load(inputStream);
+		} finally {
+			inputStream.close();
+		}
+		for (String key : properties.stringPropertyNames()) {
+			String val = properties.getProperty(key);
+			properties.setProperty(key, expandEnvVars(val));
+		}
+		return properties;
+	}
+
 	public String get(String key) {
 		return conf.get(key);
 	}
 
 	public void set(String key, String value) {
 		conf.put(key, value);
 	}
-	
+
 	public boolean getBoolean(String key, boolean fallback) {
-		if (conf.containsKey(key)){
+		if (conf.containsKey(key)) {
 			return Boolean.parseBoolean(conf.get(key));
 		} else {
 			return fallback;
@@ -59,27 +103,13 @@ public void setInt(String key, int level) {
 		String value = Integer.toString(level);
 		conf.put(key, value);
 	}
-	
+
 	private void mergeProperties(Properties properties) {
-		if (properties == null){
+		if (properties == null) {
 			return;
 		}
 		for (String key : properties.stringPropertyNames()) {
 			conf.put(key.trim(), properties.getProperty(key).trim());
 		}
 	}
-
-	private static Properties loadProperties(String resourceName) throws IOException {
-		Properties properties = new Properties();
-
-		String base = System.getenv("CRAIL_HOME");
-		FileInputStream inputStream = new FileInputStream(new File(base + "/conf/" + resourceName));
-
-		try {
-			properties.load(inputStream);
-		} finally {
-			inputStream.close();
-		}
-		return properties;
-	}
 }