To create arrays of property values add index numbers onto the end of the property keys. An array of string values * will be created with the elements of the array set to the value of the property at the matching index. Ideally the * index values will be contiguous, starting at 0. This does not need to be the case however. If an array definition * begins at index n, and ends at index m, Then an array big enough to hold m + 1 elements will be created and populated * with values from n to m. Values before n and any missing values between n and m will be null in the array. * *
To give an example, suppose you have two different environments 'DEVELOPMENT' and 'PRODUCTION' and they each need * the same properties but set to different values for each environment and some properties the same in both, you could * create a properties file like: * *
* # Project configuration properties file.
*
*
*
* # These properties are environment specific.
* DEVELOPMENT.debug=true
* PRODUCTION.debug=false
*
* # Always debug MyClass in all environments but not the myMethod method.
* MyClass.debug=true
* MyClass.myMethod.debug=false
*
* # Set up an array of my ten favourite animals. Leave elements 3 to 8 as null as I haven't decided on them yet.
* animals.0=cat
* animals.1=dog
* animals.2=elephant
* animals.9=lion
*
* # This is a default value that will be used when the environment is not known.
* debug=false
*
The most specific definition of a property is searched for first moving out to the most general. This allows * general property defaults to be set and then overiden for specific uses by some classes and modifiers. * *
A ContextualProperties object can be loaded in the same way as a java.utils.Properties. A recommended way to do * this that does not assume that the properties file is a file (it could be in a jar) is to load the properties from the * url for the resource lookup up on the classpath: * *
* Properties configProperties = new ContextualProperties();
*
*
* configProperties.load(this.getClass().getClassLoader().getResourceAsStream("config.properties"));
*
EnvironmentProperties will load the 'DEVELOPMENT.debug' property or 'PROUCTION.debug' property based on the setting * of the system environment property. If a matching property for the environment cannot be found then the simple property * name without the environment pre-pended onto it will be used instead. This 'use of default environments' behaviour is * turned on initially but it can be disabled by calling the {@link #useDefaultEnvironments} method. * *
When a property matching a key cannot be found then the property accessor methods will always return null. If a * default value for a property exists but the 'use of default environments' behavious prevents it being used then the * accessor methods will return null. * *
| Responsibilities | Collaborations * |
|---|---|
| Automatically select properties dependant on environment, class name and modifier as well as property key. * | |
| Convert indexed properties into arrays. * |
Holds the iteration count down order. * *
If e = 4, b = 2, m = 1 then the iteration order or i is 7,6,4 and then if using environment defaults 3,2,0 * where the accessor key is: * (i & e != 0 ? environment : "") + (i & b != 0 ? base : "") + (1 + m != 0 ? modifier : "") + key * *
In other words the presence or otherwise of the three least significant bits when counting down from 7 * specifies which of the environment, base and modifier are to be included in the key where the environment, base * and modifier stand for the bits in positions 2, 1 and 0. The numbers 5 and 1 are missed out of the count because * they stand for the case where the modifier is used without the base which is not done. */ private static final int[] ORDER = new int[] { 7, 6, 4, 3, 2, 0 }; /** * Defines the point in the iteration count order below which the 'use environment defaults' feature is being used. */ private static final int ENVIRONMENT_DEFAULTS_CUTOFF = 4; /** Defines the bit representation for the environment in the key ordering. See {@link #ORDER}. */ private static final int E = 4; /** Defines the bit representation for the base in the key ordering. See {@link #ORDER}. */ private static final int B = 2; /** Defines the bit representation for the modifier in the key ordering. See {@link #ORDER}. */ private static final int M = 1; /** Used to hold the value of the environment system property. */ private String environment; /** Used to indicate that the 'use of defaults' behaviour should be used. */ private boolean useDefaults = true; /** Used to hold all the array properties. This is a mapping from property names to ArrayLists of Strings. */ protected Map arrayProperties = new HashMap(); /** * Default constructor that builds a ContextualProperties that uses environment defaults. */ public ContextualProperties() { super(); // Keep the value of the system environment property. environment = System.getProperty(ENV_SYS_PROPERTY); } /** * Creates a ContextualProperties that uses environment defaults and is initialized with the specified properties. * * @param props The properties to initialize this with. */ public ContextualProperties(Properties props) { super(props); // Keep the value of the system environment property. environment = System.getProperty(ENV_SYS_PROPERTY); // Extract any array properties as arrays. createArrayProperties(); } /** * Parses an input stream as properties. * * @param inStream The input stream to read the properties from. * * @exception IOException If there is an IO error during reading from the input stream. */ public void load(InputStream inStream) throws IOException { super.load(inStream); // Extract any array properties as arrays. createArrayProperties(); } /** * Tells this environment aware properties object whether it should use default environment properties without a * pre-pended environment when a property for the current environment cannot be found. * * @param flag True to use defaults, false to not use defaults. */ public void useDefaultEnvironments(boolean flag) { useDefaults = flag; } /** * Looks up a property value relative to the environment, callers class and method. The default environment will be * checked for a matching property if defaults are being used. In order to work out the callers class and method this * method throws an exception and then searches one level up its stack frames. * * @param key The property key. * * @return The value of this property searching from the most specific definition (environment, class, method, key) * to the most general (key only), unless use of default environments is turned off in which case the most general * proeprty searched is (environment, key). */ public String getProperty(String key) { // Try to get the callers class name and method name by examing the stack. String className = null; String methodName = null; // Java 1.4 onwards only. /*try { throw new Exception(); } catch (Exception e) { StackTraceElement[] stack = e.getStackTrace(); // Check that the stack trace contains at least two elements, one for this method and one for the caller. if (stack.length >= 2) { className = stack[1].getClassName(); methodName = stack[1].getMethodName(); } }*/ // Java 1.5 onwards only. StackTraceElement[] stack = Thread.currentThread().getStackTrace(); // Check that the stack trace contains at least two elements, one for this method and one for the caller. if (stack.length >= 2) { className = stack[1].getClassName(); methodName = stack[1].getMethodName(); } // Java 1.3 and before? Not sure, some horrible thing that parses the text spat out by printStackTrace? return getProperty(className, methodName, key); } /** * Looks up a property value relative to the environment, base class and modifier. The default environment will be * checked for a matching property if defaults are being used. * * @param base An object of the class to retrieve properties relative to. * @param modifier The modifier (which may stand for a method of the class). * @param key The property key. * * @return The value of this property searching from the most specific definition (environment, class, modifier, key) * to the most general (key only), unless use of default environments is turned off in which case the most general * property searched is (environment, key). */ public String getProperty(Object base, String modifier, String key) { return getProperty(base.getClass().getName(), modifier, key); } /** * Looks up a property value relative to the environment, base class and modifier. The default environment will be * checked for a matching property if defaults are being used. * * @param base The name of the class to retrieve properties relative to. * @param modifier The modifier (which may stand for a method of the class). * @param key The property key. * * @return The value of this property searching from the most specific definition (environment, class, modifier, key) * to the most general (key only), unless use of default environments is turned off in which case the most general * property searched is (environment, key). */ public String getProperty(String base, String modifier, String key) { String result = null; // Loop over the key orderings, from the most specific to the most general, until a matching value is found. for (Iterator i = getKeyIterator(base, modifier, key); i.hasNext();) { String nextKey = (String) i.next(); result = super.getProperty(nextKey); if (result != null) { break; } } return result; } /** * Looks up an array property value relative to the environment, callers class and method. The default environment * will be checked for a matching array property if defaults are being used. In order to work out the callers class * and method this method throws an exception and then searches one level up its stack frames. * * @param key The property key. * * @return The array value of this indexed property searching from the most specific definition (environment, class, * method, key) to the most general (key only), unless use of default environments is turned off in which * case the most general proeprty searched is (environment, key). */ public String[] getProperties(String key) { // Try to get the callers class name and method name by throwing an exception an searching the stack frames. String className = null; String methodName = null; /* Java 1.4 onwards only. try { throw new Exception(); } catch (Exception e) { StackTraceElement[] stack = e.getStackTrace(); // Check that the stack trace contains at least two elements, one for this method and one for the caller. if (stack.length >= 2) { className = stack[1].getClassName(); methodName = stack[1].getMethodName(); } }*/ return getProperties(className, methodName, key); } /** * Looks up an array property value relative to the environment, base class and modifier. The default environment will * be checked for a matching array property if defaults are being used. * * @param base An object of the class to retrieve properties relative to. * @param modifier The modifier (which may stand for a method of the class). * @param key The property key. * * @return The array value of this indexed property searching from the most specific definition (environment, class, * modifier, key) to the most general (key only), unless use of default environments is turned off in which * case the most general proeprty searched is (environment, key). */ public String[] getProperties(Object base, String modifier, String key) { return getProperties(base.getClass().getName(), modifier, key); } /** * Looks up an array property value relative to the environment, base class and modifier. The default environment will * be checked for a matching array property if defaults are being used. * * @param base The name of the class to retrieve properties relative to. * @param modifier The modifier (which may stand for a method of the class). * @param key The property key. * * @return The array value of this indexed property searching from the most specific definition (environment, class, * modifier, key) to the most general (key only), unless use of default environments is turned off in which * case the most general property searched is (environment, key). */ public String[] getProperties(String base, String modifier, String key) { String[] result = null; // Loop over the key orderings, from the most specific to the most general, until a matching value is found. for (Iterator i = getKeyIterator(base, modifier, key); i.hasNext();) { String nextKey = (String) i.next(); ArrayList arrayList = (ArrayList) arrayProperties.get(nextKey); if (arrayList != null) { result = (String[]) arrayList.toArray(new String[] {}); break; } } return result; } /** * For a given environment, base, modifier and key and setting of the use of default environments feature this * generates an iterator that walks over the order in which to try and access properties. * *
See the {@link #ORDER} constant for an explanation of how the key ordering is generated. * * @param base The name of the class to retrieve properties relative to. * @param modifier The modifier (which may stand for a method of the class). * @param key The property key. * * @return An Iterator over String keys defining the order in which properties should be accessed. */ protected Iterator getKeyIterator(final String base, final String modifier, final String key) { return new Iterator() { // The key ordering count always begins at the start of the ORDER array. private int i = 0; public boolean hasNext() { return (useDefaults ? ((i < ORDER.length) && (ORDER[i] > ENVIRONMENT_DEFAULTS_CUTOFF)) : (i < ORDER.length)); } public Object next() { // Check that there is a next element and return null if not. if (!hasNext()) { return null; } // Get the next ordering count. int o = ORDER[i]; // Do bit matching on the count to choose which elements to include in the key. String result = (((o & E) != 0) ? (environment + ".") : "") + (((o & B) != 0) ? (base + ".") : "") + (((o & M) != 0) ? (modifier + ".") : "") + key; // Increment the iterator to get the next key on the next call. i++; return result; } public void remove() { // This method is not supported. throw new UnsupportedOperationException("remove() is not supported on this key order iterator as " + "the ordering cannot be changed"); } }; } /** * Scans all the properties in the parent Properties object and creates arrays for any array property definitions. * *
Array properties are defined with indexes. For example: * *
* property.1=one
*
*
* property.2=two
* property.3=three
*
Note that these properties will be stored as the 'empty string' or "" property array. * *
* .1=one
*/
protected void createArrayProperties()
{
// Scan through all defined properties.
for (Object o : keySet())
{
String key = (String) o;
String value = super.getProperty(key);
// Split the property key into everything before the last '.' and after it.
int lastDotIndex = key.lastIndexOf('.');
String keyEnding = key.substring(lastDotIndex + 1, key.length());
String keyStart = key.substring(0, (lastDotIndex == -1) ? 0 : lastDotIndex);
// Check if the property key ends in an integer, in which case it is an array property.
int index = 0;
try
{
index = Integer.parseInt(keyEnding);
}
// The ending is not an integer so its not an array.
catch (NumberFormatException e)
{
// Scan the next property.
continue;
}
// Check if an array property already exists for this base name and create one if not.
ArrayList propArray = (ArrayList) arrayProperties.get(keyStart);
if (propArray == null)
{
propArray = new ArrayList();
arrayProperties.put(keyStart, propArray);
}
// Add the new property value to the array property for the index.
propArray.set(index, value);
}
}
}
* 2=two
*