Examples of org.apache.commons.configuration.interpol.ConfigurationInterpolator

Package org.apache.commons.configuration.interpol

Examples of org.apache.commons.configuration.interpol.ConfigurationInterpolator

org.apache.commons.configuration.interpol.ConfigurationInterpolator

ns.apache.org/lang">Commons Lang. By extending StrLookup it is able to provide values for variables that appear in expressions.

The basic idea of this class is that it can maintain a set of primitive StrLookup objects, each of which is identified by a special prefix. The variables to be processed have the form ${prefix:name}. ConfigurationInterpolator will extract the prefix and determine, which primitive lookup object is registered for it. Then the name of the variable is passed to this object to obtain the actual value. It is also possible to define a default lookup object, which will be used for variables that do not have a prefix or that cannot be resolved by their associated lookup object.

When a new instance of this class is created it is initialized with a default set of primitive lookup objects. This set can be customized using the static methods registerGlobalLookup() and deregisterGlobalLookup(). Per default it contains the following standard lookup objects:

Prefix	Lookup object
sys	With this prefix a lookup object is associated that is able to resolve system properties.
const	The `const` prefix indicates that a variable is to be interpreted as a constant member field of a class (i.e. a field with the static final modifiers). The name of the variable must be of the form `<full qualified class name>.<field name>`, e.g. `org.apache.commons.configuration.interpol.ConfigurationInterpolator.PREFIX_CONSTANTS` .

After an instance has been created the current set of lookup objects can be modified using the registerLookup() and deregisterLookup() methods. The default lookup object (that is invoked for variables without a prefix) can be set with the setDefaultLookup() method. (If a ConfigurationInterpolator instance is created by a configuration object, this lookup points to the configuration itself, so that variables are resolved using the configuration's properties. This ensures backward compatibility to earlier version of Commons Configuration.)

Implementation node: Instances of this class are not thread-safe related to modifications of their current set of registered lookup objects. It is intended that each instance is associated with a single Configuration object and used for its interpolation tasks.

@version $Id: ConfigurationInterpolator.java 561230 2007-07-31 04:17:09Z rahul $ @since 1.4 @author Commons Configuration team

        boolean success;
        do
        {
            // do this in a loop because the ConfigurationInterpolator
            // instance may be changed by another thread
            ConfigurationInterpolator ciOld = getInterpolator();
            ConfigurationInterpolator ciNew =
                    (ciOld != null) ? ciOld : new ConfigurationInterpolator();
            ciNew.registerLookups(lookups);
            success = interpolator.compareAndSet(ciOld, ciNew);
        } while (!success);
    }

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    public void setDefaultLookups(Collection<? extends Lookup> lookups)
    {
        boolean success;
        do
        {
            ConfigurationInterpolator ciOld = getInterpolator();
            ConfigurationInterpolator ciNew =
                    (ciOld != null) ? ciOld : new ConfigurationInterpolator();
            Lookup confLookup = findConfigurationLookup(ciNew);
            if (confLookup == null)
            {
                confLookup = new ConfigurationLookup(this);
            }
            else
            {
                ciNew.removeDefaultLookup(confLookup);
            }
            ciNew.addDefaultLookups(lookups);
            ciNew.addDefaultLookup(confLookup);
            success = interpolator.compareAndSet(ciOld, ciNew);
        } while (!success);
    }

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    public void setParentInterpolator(ConfigurationInterpolator parent)
    {
        boolean success;
        do
        {
            ConfigurationInterpolator ciOld = getInterpolator();
            ConfigurationInterpolator ciNew =
                    (ciOld != null) ? ciOld : new ConfigurationInterpolator();
            ciNew.setParentInterpolator(parent);
            success = interpolator.compareAndSet(ciOld, ciNew);
        } while (!success);
    }

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     * @since 2.0
     */
    protected void cloneInterpolator(AbstractConfiguration orgConfig)
    {
        interpolator = new AtomicReference<ConfigurationInterpolator>();
        ConfigurationInterpolator orgInterpolator = orgConfig.getInterpolator();
        List<Lookup> defaultLookups = orgInterpolator.getDefaultLookups();
        Lookup lookup = findConfigurationLookup(orgInterpolator, orgConfig);
        if (lookup != null)
        {
            defaultLookups.remove(lookup);
        }


        installInterpolator(orgInterpolator.getLookups(), defaultLookups);
    }

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     * @param value the value to interpolate
     * @return the value with variables substituted
     */
    protected Object interpolate(Object value)
    {
        ConfigurationInterpolator ci = getInterpolator();
        return (ci != null) ? ci.interpolate(value) : value;
    }

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     * @return the newly created interpolator object
     * @since 1.4
     */
    protected ConfigurationInterpolator createInterpolator()
    {
        ConfigurationInterpolator interpol = new ConfigurationInterpolator();
        interpol.setDefaultLookup(new StrLookup()
        {
            public String lookup(String var)
            {
                Object prop = resolveContainerStore(var);
                return (prop != null) ? prop.toString() : null;

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     * Tests accessing and manipulating the interpolator object.
     */
    public void testGetInterpolator()
    {
        config.addProperty("var", "${echo:testVar}");
        ConfigurationInterpolator interpol = config.getInterpolator();
        interpol.registerLookup("echo", new StrLookup()
        {
            public String lookup(String varName)
            {
                return "Value of variable " + varName;
            }

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         * @param config the newly created configuration instance
         */
        private void installInterpolator(ConfigurationDeclaration decl,
                AbstractConfiguration config)
        {
            ConfigurationInterpolator parent = new ConfigurationInterpolator();
            parent.setDefaultLookup(decl.getConfigurationBuilder().combinedConfigLookup);
            config.getInterpolator().setParentInterpolator(parent);
        }

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            return super.interpolate(base);
        }
        else
        {
            SubsetConfiguration config = new SubsetConfiguration(parent, "");
            ConfigurationInterpolator interpolator = config.getInterpolator();
            getInterpolator().registerLocalLookups(interpolator);
            if (parent instanceof AbstractConfiguration)
            {
                interpolator.setParentInterpolator(((AbstractConfiguration) parent).getInterpolator());
            }
            return config.interpolate(base);
        }
    }

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     * @param config the configuration to test
     */
    public static void testGetInterpolator(AbstractConfiguration config)
    {
        config.addProperty("var", "${echo:testVar}");
        ConfigurationInterpolator interpol = config.getInterpolator();
        interpol.registerLookup("echo", new StrLookup()
        {
            @Override
            public String lookup(String varName)
            {
                return "Value of variable " + varName;

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