java/jakarta/el/StandardELContext.java

/*
 * 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 jakarta.el;

import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;

/**
 * Standard implementation of {@link ELContext} that provides a complete EL resolution environment. It maintains a
 * composite resolver chain, variable mapper, function mapper, and supports custom resolvers and local beans. This is
 * the default context implementation used by {@link ELProcessor}.
 *
 * @since EL 3.0
 */
public class StandardELContext extends ELContext {

    private final ELContext wrappedContext;
    private final VariableMapper variableMapper;
    private final FunctionMapper functionMapper;
    private final CompositeELResolver standardResolver;
    private final CompositeELResolver customResolvers;
    private final Map<String,Object> localBeans = new HashMap<>();


    /**
     * Constructs a new instance backed by the given expression factory.
     * <p>
     * Initializes the standard resolver chain with built-in resolvers and
     * a function mapper populated from the factory's initial function map.
     *
     * @param factory the expression factory providing the initial resolver and function configuration
     */
    public StandardELContext(ExpressionFactory factory) {
        wrappedContext = null;
        variableMapper = new StandardVariableMapper();
        functionMapper = new StandardFunctionMapper(factory.getInitFunctionMap());
        standardResolver = new CompositeELResolver();
        customResolvers = new CompositeELResolver();

        ELResolver streamResolver = factory.getStreamELResolver();

        // Add resolvers in order
        standardResolver.add(new BeanNameELResolver(new StandardBeanNameResolver(localBeans)));
        standardResolver.add(customResolvers);
        if (streamResolver != null) {
            standardResolver.add(streamResolver);
        }
        standardResolver.add(new StaticFieldELResolver());
        standardResolver.add(new MapELResolver());
        standardResolver.add(new ResourceBundleELResolver());
        standardResolver.add(new ListELResolver());
        standardResolver.add(new ArrayELResolver());
        standardResolver.add(new RecordELResolver());
        standardResolver.add(new BeanELResolver());
    }

    /**
     * Constructs a new instance that wraps the given context.
     * <p>
     * The variable mapper, function mapper, and EL resolver from the wrapped
     * context are used, with additional standard resolvers prepended.
     *
     * @param context the context to wrap
     */
    public StandardELContext(ELContext context) {
        wrappedContext = context;
        variableMapper = context.getVariableMapper();
        functionMapper = context.getFunctionMapper();
        standardResolver = new CompositeELResolver();
        customResolvers = new CompositeELResolver();

        // Add resolvers in order
        standardResolver.add(new BeanNameELResolver(new StandardBeanNameResolver(localBeans)));
        standardResolver.add(customResolvers);
        // Use resolvers from context from this point on
        standardResolver.add(context.getELResolver());
    }

    @Override
    public void putContext(Class<?> key, Object contextObject) {
        if (wrappedContext == null) {
            super.putContext(key, contextObject);
        } else {
            wrappedContext.putContext(key, contextObject);
        }
    }

    @Override
    public Object getContext(Class<?> key) {
        if (wrappedContext == null) {
            return super.getContext(key);
        } else {
            return wrappedContext.getContext(key);
        }
    }

    @Override
    public ELResolver getELResolver() {
        return standardResolver;
    }

    /**
     * Adds a custom EL resolver to the resolver chain.
     * <p>
     * Custom resolvers are inserted after the bean name resolver and before
     * the standard resolvers, allowing them to intercept resolution before
     * the built-in resolvers are consulted.
     *
     * @param resolver the resolver to add
     */
    public void addELResolver(ELResolver resolver) {
        customResolvers.add(resolver);
    }

    @Override
    public FunctionMapper getFunctionMapper() {
        return functionMapper;
    }

    @Override
    public VariableMapper getVariableMapper() {
        return variableMapper;
    }


    Map<String,Object> getLocalBeans() {
        return localBeans;
    }


    private static class StandardVariableMapper extends VariableMapper {

        private Map<String,ValueExpression> vars;

        @Override
        public ValueExpression resolveVariable(String variable) {
            if (vars == null) {
                return null;
            }
            return vars.get(variable);
        }

        @Override
        public ValueExpression setVariable(String variable, ValueExpression expression) {
            if (vars == null) {
                vars = new HashMap<>();
            }
            if (expression == null) {
                return vars.remove(variable);
            } else {
                return vars.put(variable, expression);
            }
        }
    }


    private static class StandardBeanNameResolver extends BeanNameResolver {

        private final Map<String,Object> beans;

        StandardBeanNameResolver(Map<String,Object> beans) {
            this.beans = beans;
        }

        @Override
        public boolean isNameResolved(String beanName) {
            return beans.containsKey(beanName);
        }

        @Override
        public Object getBean(String beanName) {
            return beans.get(beanName);
        }

        @Override
        public void setBeanValue(String beanName, Object value) throws PropertyNotWritableException {
            beans.put(beanName, value);
        }

        @Override
        public boolean isReadOnly(String beanName) {
            return false;
        }

        @Override
        public boolean canCreateBean(String beanName) {
            return true;
        }
    }


    private static class StandardFunctionMapper extends FunctionMapper {

        private final Map<String,Method> methods = new HashMap<>();

        StandardFunctionMapper(Map<String,Method> initFunctionMap) {
            if (initFunctionMap != null) {
                methods.putAll(initFunctionMap);
            }
        }

        @Override
        public Method resolveFunction(String prefix, String localName) {
            String key = prefix + ':' + localName;
            return methods.get(key);
        }

        @Override
        public void mapFunction(String prefix, String localName, Method method) {
            String key = prefix + ':' + localName;
            if (method == null) {
                methods.remove(key);
            } else {
                methods.put(key, method);
            }
        }
    }
}