ELServiceInternal.java

/**
 * Copyright (c) 2013-2016, The SeedStack authors <http://seedstack.org>
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */
package org.seedstack.seed.core.internal.el;

import com.google.common.base.Strings;
import org.seedstack.seed.SeedException;
import org.seedstack.seed.el.ELService;

import javax.el.ELContext;
import javax.el.ELException;
import javax.el.ExpressionFactory;
import javax.el.MethodExpression;
import javax.el.PropertyNotFoundException;
import javax.el.ValueExpression;
import javax.inject.Inject;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

/**
 * Implementation of ELService.
 */
class ELServiceInternal implements ELService {
    @Inject
    private ExpressionFactory expressionFactory;

    @Override
    public ELContextProvider withExpression(String el, Class returnType) {
        checkArgument(!Strings.isNullOrEmpty(el), "An expression is required");
        checkNotNull(returnType, "The return type must not be null");
        return new ELInstance(expressionFactory, el, returnType);
    }

    @Override
    public ValueExpressionProvider withValueExpression(ValueExpression valueExpression) {
        checkNotNull(valueExpression, "The value expression must not be null");
        ELInstance elInstance = new ELInstance(expressionFactory);
        elInstance.setValueExpression(valueExpression);
        return elInstance;
    }

    @Override
    public MethodExpressionProvider withMethodExpression(MethodExpression methodExpression) {
        checkNotNull(methodExpression, "The method expression must not be null");
        ELInstance elInstance = new ELInstance(expressionFactory);
        elInstance.setMethodExpression(methodExpression);
        return elInstance;
    }

    private static class ELInstance implements ELContextProvider, ELExpressionProvider, ELService.MethodExpressionProvider, ELService.ValueExpressionProvider {
        private final ExpressionFactory expressionFactory;
        private String el;
        private Class returnType;
        private MethodExpression methodExpression;
        private ValueExpression valueExpression;
        private ELContext context;

        ELInstance(ExpressionFactory expressionFactory) {
            this.expressionFactory = expressionFactory;
        }

        ELInstance(ExpressionFactory expressionFactory, String el, Class returnType) {
            this.expressionFactory = expressionFactory;
            this.el = el;
            this.returnType = returnType;
        }

        @Override
        public ELExpressionProvider withContext(ELContext elContext) {
            checkNotNull(elContext, "The context must not be null");
            context = elContext;
            return this;
        }

        @Override
        public ELExpressionProvider withDefaultContext() {
            context = ELContextBuilderImpl.createDefaultELContext(expressionFactory);
            return this;
        }

        @Override
        public ValueExpression valueExpression() {
            return valueExpression;
        }

        @Override
        public ValueExpressionProvider asValueExpression() {
            valueExpression = expressionFactory.createValueExpression(context, el, returnType);
            return this;
        }

        @Override
        public MethodExpression methodExpression() {
            return methodExpression;
        }

        @Override
        public MethodExpressionProvider asMethodExpression(Class<?>[] expectedParamTypes) {
            methodExpression = expressionFactory.createMethodExpression(context, el, returnType, expectedParamTypes);
            return this;
        }

        @Override
        public Object eval() {
            Object value;
            try {
                value = valueExpression.getValue(context);
            } catch (PropertyNotFoundException e) {
                throw SeedException.wrap(e, ExpressionLanguageErrorCode.PROPERTY_NOT_FOUND).put("el", el);
            } catch (ELException e) {
                throw SeedException.wrap(e, ExpressionLanguageErrorCode.EL_EXCEPTION).put("el", el);
            }
            return value;
        }

        @Override
        public Object invoke(Object[] args) {
            Object value;
            try {
                value = methodExpression.invoke(context, args);
            } catch (PropertyNotFoundException e) {
                throw SeedException.wrap(e, ExpressionLanguageErrorCode.PROPERTY_NOT_FOUND).put("el", el);
            } catch (ELException e) {
                throw SeedException.wrap(e, ExpressionLanguageErrorCode.EL_EXCEPTION).put("el", el);
            }
            return value;
        }

        void setMethodExpression(MethodExpression methodExpression) {
            this.methodExpression = methodExpression;
        }

        void setValueExpression(ValueExpression valueExpression) {
            this.valueExpression = valueExpression;
        }
    }
}