org.apache.commons.configuration.interpol.ExprLookup Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.
*/
package org.apache.commons.configuration.interpol;
import java.util.ArrayList;
import org.apache.commons.configuration.AbstractConfiguration;
import org.apache.commons.configuration.ConfigurationRuntimeException;
import org.apache.commons.jexl2.Expression;
import org.apache.commons.jexl2.JexlContext;
import org.apache.commons.jexl2.JexlEngine;
import org.apache.commons.jexl2.MapContext;
import org.apache.commons.lang.ClassUtils;
import org.apache.commons.lang.StringUtils;
import org.apache.commons.lang.text.StrLookup;
import org.apache.commons.lang.text.StrSubstitutor;
/**
* Lookup that allows expressions to be evaluated.
*
*
* ExprLookup.Variables vars = new ExprLookup.Variables();
* vars.add(new ExprLookup.Variable("String", org.apache.commons.lang.StringUtils.class));
* vars.add(new ExprLookup.Variable("Util", new Utility("Hello")));
* vars.add(new ExprLookup.Variable("System", "Class:java.lang.System"));
* XMLConfiguration config = new XMLConfiguration(TEST_FILE);
* config.setLogger(log);
* ExprLookup lookup = new ExprLookup(vars);
* lookup.setConfiguration(config);
* String str = lookup.lookup("'$[element] ' + String.trimToEmpty('$[space.description]')");
*
*
* In the example above TEST_FILE contains xml that looks like:
*
* <configuration>
* <element>value</element>
* <space xml:space="preserve">
* <description xml:space="default"> Some text </description>
* </space>
* </configuration>
*
*
* The result will be "value Some text".
*
* This lookup uses Apache Commons Jexl and requires that the dependency be added to any
* projects which use this.
*
* @since 1.7
* @author Commons Configuration team
* @version $Id: ExprLookup.java 1234539 2012-01-22 16:19:15Z oheger $
*/
public class ExprLookup extends StrLookup
{
/** Prefix to identify a Java Class object */
private static final String CLASS = "Class:";
/** The default prefix for subordinate lookup expressions */
private static final String DEFAULT_PREFIX = "$[";
/** The default suffix for subordinate lookup expressions */
private static final String DEFAULT_SUFFIX = "]";
/** Configuration being operated on */
private AbstractConfiguration configuration;
/** The engine. */
private final JexlEngine engine = new JexlEngine();
/** The variables maintained by this object. */
private Variables variables;
/** The String to use to start subordinate lookup expressions */
private String prefixMatcher = DEFAULT_PREFIX;
/** The String to use to terminate subordinate lookup expressions */
private String suffixMatcher = DEFAULT_SUFFIX;
/**
* The default constructor. Will get used when the Lookup is constructed via
* configuration.
*/
public ExprLookup()
{
}
/**
* Constructor for use by applications.
* @param list The list of objects to be accessible in expressions.
*/
public ExprLookup(Variables list)
{
setVariables(list);
}
/**
* Constructor for use by applications.
* @param list The list of objects to be accessible in expressions.
* @param prefix The prefix to use for subordinate lookups.
* @param suffix The suffix to use for subordinate lookups.
*/
public ExprLookup(Variables list, String prefix, String suffix)
{
this(list);
setVariablePrefixMatcher(prefix);
setVariableSuffixMatcher(suffix);
}
/**
* Set the prefix to use to identify subordinate expressions. This cannot be the
* same as the prefix used for the primary expression.
* @param prefix The String identifying the beginning of the expression.
*/
public void setVariablePrefixMatcher(String prefix)
{
prefixMatcher = prefix;
}
/**
* Set the suffix to use to identify subordinate expressions. This cannot be the
* same as the suffix used for the primary expression.
* @param suffix The String identifying the end of the expression.
*/
public void setVariableSuffixMatcher(String suffix)
{
suffixMatcher = suffix;
}
/**
* Add the Variables that will be accessible within expressions.
* @param list The list of Variables.
*/
public void setVariables(Variables list)
{
variables = new Variables(list);
}
/**
* Returns the list of Variables that are accessible within expressions.
* @return the List of Variables that are accessible within expressions.
*/
public Variables getVariables()
{
return null;
}
/**
* Set the configuration to be used to interpolate subordinate expressions.
* @param config The Configuration.
*/
public void setConfiguration(AbstractConfiguration config)
{
this.configuration = config;
}
/**
* Evaluates the expression.
* @param var The expression.
* @return The String result of the expression.
*/
@Override
public String lookup(String var)
{
ConfigurationInterpolator interp = configuration.getInterpolator();
StrSubstitutor subst = new StrSubstitutor(interp, prefixMatcher, suffixMatcher,
StrSubstitutor.DEFAULT_ESCAPE);
String result = subst.replace(var);
try
{
Expression exp = engine.createExpression(result);
result = (String) exp.evaluate(createContext());
}
catch (Exception e)
{
configuration.getLogger().debug("Error encountered evaluating " + result, e);
}
return result;
}
/**
* Creates a new {@code JexlContext} and initializes it with the variables
* managed by this Lookup object.
*
* @return the newly created context
*/
private JexlContext createContext()
{
JexlContext ctx = new MapContext();
initializeContext(ctx);
return ctx;
}
/**
* Initializes the specified context with the variables managed by this
* Lookup object.
*
* @param ctx the context to be initialized
*/
private void initializeContext(JexlContext ctx)
{
for (Variable var : variables)
{
ctx.set(var.getName(), var.getValue());
}
}
/**
* List wrapper used to allow the Variables list to be created as beans in
* DefaultConfigurationBuilder.
*/
public static class Variables extends ArrayList
{
/**
* The serial version UID.
*/
private static final long serialVersionUID = 20111205L;
/**
* Creates a new empty instance of {@code Variables}.
*/
public Variables()
{
super();
}
/**
* Creates a new instance of {@code Variables} and copies the content of
* the given object.
*
* @param vars the {@code Variables} object to be copied
*/
public Variables(Variables vars)
{
super(vars);
}
public Variable getVariable()
{
if (size() > 0)
{
return get(size() - 1);
}
else
{
return null;
}
}
}
/**
* The key and corresponding object that will be made available to the
* JexlContext for use in expressions.
*/
public static class Variable
{
/** The name to be used in expressions */
private String key;
/** The object to be accessed in expressions */
private Object value;
public Variable()
{
}
public Variable(String name, Object value)
{
setName(name);
setValue(value);
}
public String getName()
{
return key;
}
public void setName(String name)
{
this.key = name;
}
public Object getValue()
{
return value;
}
public void setValue(Object value) throws ConfigurationRuntimeException
{
try
{
if (!(value instanceof String))
{
this.value = value;
return;
}
String val = (String) value;
String name = StringUtils.removeStartIgnoreCase(val, CLASS);
Class clazz = ClassUtils.getClass(name);
if (name.length() == val.length())
{
this.value = clazz.newInstance();
}
else
{
this.value = clazz;
}
}
catch (Exception e)
{
throw new ConfigurationRuntimeException("Unable to create " + value, e);
}
}
}
}
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