Properties Loader a Helper Class

Listed is the code for Property Loader a Helper class to load properties both from a file and from system.
This

  1. We can load file each time to read a property using getProperty(key) Method
  2. We can read properties loaded when class is loaded and are can be read from system properties where it is set
  3. It also has utility where we can Cast Property Values to Custom Type like Long/Int..etc
  4. It has implementation of adding parameters dynamically in property file by placing some placeholders


import java.io.IOException;
import java.io.InputStream;
import java.util.Iterator;
import java.util.Properties;

import javax.servlet.ServletContext;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
* @author Ashwin Gets System variables that were loaded at server startup from
* the server.properties file
*/
public class PropertyLoader {
private static final Log log = LogFactory.getLog(PropertyLoader.class);
private static boolean initializedFromFile = false;

/**
* Get the Property From Server.properties. This is used when we want to
* read property from file each and every time
*
* @param key
* @return
*/
public static String getProperty(String key) {
Properties props = new Properties();
InputStream stream = PropertyLoader.class
.getResourceAsStream("/server.properties");
try {
props.load(stream);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return props.getProperty(key);
}

/**
* This is used when we just want to load all properties loaded and are sure
* that those dont change while server is running thereby reducing load of
* reading from file
*
* Get the value of the key passed.
*
* @param key
* the token
* @return the value if there is one, otherwise null
*/
public static final String getSystemString(String key) {
String value = null;
try {
value = System.getProperty(key);

} catch (NullPointerException e) {
// ignore just return null;
}
return value;
}

/**
* Gets the boolean value if the string equalsIgnoreCase true, otherwise
* false.
*
* @param key
* the token
* @return true if the value is ignorecase true all other values including
* null return false.
*/
public static final boolean getBoolean(String key) {
String token = getSystemString(key);
if (token == null) {
return false;
}
if (token.equalsIgnoreCase("true")) {
return true;
}
return false;
}

public static final void loadSystemProperties() throws IOException {
loadSystemProperties("/server.properties");
}

/**
* Give the classpath qualified name of the filename to load, e.g.
*
*

	 *  /config.properties
	 * 

*
* @param file
* the classpath qualified filename of the file to load
*/
public static final void loadSystemProperties(String file)
throws IOException {
Properties props = new Properties();
InputStream stream = PropertyLoader.class.getResourceAsStream(file);
props.load(stream);

Iterator iterator = props.keySet().iterator();
while (iterator.hasNext()) {
String key = (String) iterator.next();
String value = props.getProperty(key);
System.getProperties().setProperty(key, value);
}
initializedFromFile = true;
}

/**
* Sets the property and returns the previous value
*
* @param key
* @param value
*/
public static final String setSystemProperty(String key, String value) {
if (!initializedFromFile) {
log
.warn("Attempting to set System Property "
+ key
+ " to "
+ value
+ " but the file System Properties have not yet been read.");
}
return System.setProperty(key, value);
}

/**
* Replaces all config parameters in the string with the actual values.
* Parameters are in the form ${PARAM_NAME}. If a parameter tag is
* encountered, and the corresponding value cannot be retrieved, an
* exception will be generated.
*/
public static void resolveParameterTags(StringBuffer sb) {
int basePos = 0;
String rstr = sb.toString();
final String tagStartToken = "${";
final String tagEndToken = "}";
int pos = rstr.indexOf(tagStartToken);

while (pos >= 0) {
int endPos = rstr.indexOf(tagEndToken, pos);

if (endPos < 0) {
String msg = "Parameter tag not closed: " + rstr;
throw new IllegalArgumentException(msg);
}

String pName = rstr.substring(pos + tagStartToken.length(), endPos);
String parameterValue = getSystemString(pName);

if (parameterValue == null || "".equals(parameterValue)) {
String msg = "Missing configuration parameter " + pName
+ " for tag " + rstr;
throw new IllegalArgumentException(msg);
}

// replace the parameter
sb.replace(basePos + pos, basePos + endPos + tagEndToken.length(),
parameterValue);

// point base position to the rest of the string
basePos = basePos + pos + parameterValue.length();
rstr = sb.substring(basePos);
pos = rstr.indexOf(tagStartToken);
}
}

public static long getLong(String key, long i) {
String token = getSystemString(key);
if (token == null) {
return i;
}
return Long.parseLong(token);
}

public static int getInt(String key, int i) {
String token = getSystemString(key);
if (token == null) {
return i;
}
return Integer.parseInt(token);
}

public static void loadSystemProperties(ServletContext servletContext,
String file) throws IOException {
// TODO Auto-generated method stub
Properties props = new Properties();
InputStream stream = servletContext.getResourceAsStream(file);
props.load(stream);

Iterator iterator = props.keySet().iterator();
while (iterator.hasNext()) {
String key = (String) iterator.next();
String value = props.getProperty(key);
System.getProperties().setProperty(key, value);
}
initializedFromFile = true;

}
}

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