Java tutorial
/* * (C) Copyright 2015 Netcentric AG. * * All rights reserved. This program and the accompanying materials * are made available under the terms of the Eclipse Public License v1.0 * which accompanies this distribution, and is available at * http://www.eclipse.org/legal/epl-v10.html */ package biz.netcentric.cq.tools.actool.configreader; import java.beans.FeatureDescriptor; import java.lang.reflect.Method; import java.util.HashMap; import java.util.Iterator; import java.util.Map; import javax.el.ArrayELResolver; import javax.el.BeanELResolver; import javax.el.CompositeELResolver; import javax.el.ELContext; import javax.el.ELResolver; import javax.el.ExpressionFactory; import javax.el.FunctionMapper; import javax.el.ListELResolver; import javax.el.MapELResolver; import javax.el.ValueExpression; import javax.el.VariableMapper; import org.apache.commons.lang.ArrayUtils; import org.apache.commons.lang.StringUtils; /** Evaluates expressions that may contain variables from for loops. * * Not an OSGi Service as it carries state and is not multi-threading safe. * * @author ghenzler */ public class YamlMacroElEvaluator { private ExpressionFactory expressionFactory; private ELContext context; private Map<? extends Object, ? extends Object> vars = new HashMap<Object, Object>(); public YamlMacroElEvaluator() { try { Class<?> expressionFactoryClass = getClass().getClassLoader() .loadClass("org.apache.el.ExpressionFactoryImpl"); expressionFactory = (ExpressionFactory) expressionFactoryClass.newInstance(); } catch (ClassNotFoundException | InstantiationException | IllegalAccessException e) { throw new IllegalStateException("Could not init EL: " + e); } final VariableMapper variableMapper = new ElVariableMapper(); final ElFunctionMapper functionMapper = new ElFunctionMapper(); final CompositeELResolver compositeELResolver = new CompositeELResolver(); compositeELResolver.add(new BaseELResolver()); compositeELResolver.add(new ArrayELResolver()); compositeELResolver.add(new ListELResolver()); compositeELResolver.add(new BeanELResolver()); compositeELResolver.add(new MapELResolver()); context = new ELContext() { @Override public ELResolver getELResolver() { return compositeELResolver; } @Override public FunctionMapper getFunctionMapper() { return functionMapper; } @Override public VariableMapper getVariableMapper() { return variableMapper; } }; } public <T> T evaluateEl(String el, Class<T> expectedResultType, Map<? extends Object, ? extends Object> variables) { vars = variables; ValueExpression expression = expressionFactory.createValueExpression(context, el, expectedResultType); T value = (T) expression.getValue(context); return value; } class ElFunctionMapper extends FunctionMapper { private Map<String, Method> functionMap = new HashMap<String, Method>(); public ElFunctionMapper() { try { Method[] exportedMethods = new Method[] { StringUtils.class.getMethod("split", new Class<?>[] { String.class, String.class }), StringUtils.class.getMethod("join", new Class<?>[] { Object[].class, String.class }), ArrayUtils.class.getMethod("subarray", new Class<?>[] { Object[].class, int.class, int.class }), StringUtils.class.getMethod("upperCase", new Class<?>[] { String.class }), StringUtils.class.getMethod("lowerCase", new Class<?>[] { String.class }), StringUtils.class.getMethod("substringAfter", new Class<?>[] { String.class, String.class }), StringUtils.class.getMethod("substringBefore", new Class<?>[] { String.class, String.class }), StringUtils.class.getMethod("substringAfterLast", new Class<?>[] { String.class, String.class }), StringUtils.class.getMethod("substringBeforeLast", new Class<?>[] { String.class, String.class }), StringUtils.class.getMethod("contains", new Class<?>[] { String.class, String.class }), StringUtils.class.getMethod("endsWith", new Class<?>[] { String.class, String.class }), StringUtils.class.getMethod("startsWith", new Class<?>[] { String.class, String.class }) }; for (Method method : exportedMethods) { functionMap.put(method.getName(), method); } } catch (NoSuchMethodException e) { throw new IllegalStateException("Class StringUtils/ArrayUtils is missing expected methods", e); } } @Override public Method resolveFunction(String prefix, String localName) { String key = (StringUtils.isNotBlank(prefix) ? prefix + ":" : "") + localName; return functionMap.get(key); } } class ElVariableMapper extends VariableMapper { @Override public ValueExpression resolveVariable(String paramString) { Object value = vars.get(paramString); return value != null ? expressionFactory.createValueExpression(value, value.getClass()) : null; } @Override public ValueExpression setVariable(String paramString, ValueExpression paramValueExpression) { throw new UnsupportedOperationException(); } } /** extra base resolver needed to allow to put maps on root level, see * http://illegalargumentexception.blogspot.com.es/2008/04/java-using-el-outside-j2ee.html */ class BaseELResolver extends ELResolver { private ELResolver delegate = new MapELResolver(); public BaseELResolver() { } @Override public Object getValue(ELContext context, Object base, Object property) { if (base == null) { base = vars; } return delegate.getValue(context, base, property); } @Override public Class<?> getCommonPropertyType(ELContext context, Object base) { if (base == null) { base = vars; } return delegate.getCommonPropertyType(context, base); } @Override public Iterator<FeatureDescriptor> getFeatureDescriptors(ELContext context, Object base) { if (base == null) { base = vars; } return delegate.getFeatureDescriptors(context, base); } @Override public Class<?> getType(ELContext context, Object base, Object property) { if (base == null) { base = vars; } return delegate.getType(context, base, property); } @Override public boolean isReadOnly(ELContext context, Object base, Object property) { if (base == null) { base = vars; } return delegate.isReadOnly(context, base, property); } @Override public void setValue(ELContext context, Object base, Object property, Object value) { if (base == null) { base = vars; } delegate.setValue(context, base, property, value); } } }