org.primefaces.component.importconstants.ImportConstantsTagHandler Maven / Gradle / Ivy

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/**
 * Copyright 2009-2018 PrimeTek.
 *
 * Licensed 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.primefaces.component.importconstants;

import java.io.IOException;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.Collections;
import java.util.Map;

import javax.el.ELContext;
import javax.el.ExpressionFactory;
import javax.el.ValueExpression;
import javax.faces.FacesException;
import javax.faces.application.ProjectStage;
import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;
import javax.faces.view.facelets.FaceletContext;
import javax.faces.view.facelets.TagAttribute;
import javax.faces.view.facelets.TagConfig;
import javax.faces.view.facelets.TagHandler;
import org.primefaces.context.RequestContext;
import org.primefaces.util.SharedStringBuilder;

/**
 * {@link TagHandler} for the ImportConstants component.
 */
public class ImportConstantsTagHandler extends TagHandler {

    private static final String SB_VAR = ImportConstantsTagHandler.class.getName() + "#var";
    
    private final TagAttribute typeTagAttribute;
    private final TagAttribute varTagAttribute;

    public ImportConstantsTagHandler(TagConfig config) {
        super(config);

        typeTagAttribute = super.getRequiredAttribute("type");
        varTagAttribute = super.getAttribute("var");
    }

    @Override
    public void apply(FaceletContext ctx, UIComponent parent) throws IOException {

        FacesContext facesContext = FacesContext.getCurrentInstance();

        Class type = getClassFromAttribute(typeTagAttribute, ctx);
        Map constants = getConstants(facesContext, type);

        // Create alias/var expression
        String var;
        if (varTagAttribute == null) {
            var = type.getSimpleName(); // fall back to class name
        }
        else {
            var = varTagAttribute.getValue(ctx);
        }

        if (var.charAt(0) != '#') {
            StringBuilder varBuilder = SharedStringBuilder.get(facesContext, SB_VAR, var.length() + 3);
            varBuilder.append("#{").append(var).append("}");

            var = varBuilder.toString();
        }

        // Assign constants to alias/var expression
        ELContext elContext = facesContext.getELContext();
        ExpressionFactory expressionFactory = facesContext.getApplication().getExpressionFactory();

        ValueExpression aliasValueExpression = expressionFactory.createValueExpression(elContext, var, Map.class);
        aliasValueExpression.setValue(elContext, constants);
    }

    /**
     * Gets the {@link Class} from the {@link TagAttribute}.
     *
     * @param attribute The {@link TagAttribute}.
     * @param ctx The {@link FaceletContext}.
     * @return The {@link Class}.
     */
    protected Class getClassFromAttribute(TagAttribute attribute, FaceletContext ctx) {
        String type = attribute.getValue(ctx);

        try {
            return Class.forName(type, true, Thread.currentThread().getContextClassLoader());
        }
        catch (ClassNotFoundException e) {
            throw new FacesException("Class " + type + " not found.", e);
        }
    }

    /**
     * Get all constants of the given {@link Class}.
     *
     * @param facesContext The {@link FacesContext}.
     * @param type The class which includes the constants.
     * @return A {@link Map} with the constants.
     */
    protected Map getConstants(FacesContext facesContext, Class type) {
        boolean cacheEnabled = facesContext.isProjectStage(ProjectStage.Production);
        Map, Map> cache
                = RequestContext.getCurrentInstance().getApplicationContext().getConstantsCacheMap();

        Map constants;

        if (cacheEnabled && cache.containsKey(type)) {
            constants = cache.get(type);
        }
        else {
            constants = Collections.unmodifiableMap(collectConstants(type));

            if (cacheEnabled) {
                cache.put(type, constants);
            }
        }

        return constants;
    }

    /**
     * Collects all constants of the given {@link Class}.
     *
     * @param type The class which includes the constants.
     * @return A {@link Map} with the found constants.
     */
    protected Map collectConstants(Class type) {
        Map constants = new ConstantsHashMap(type);

        // Go through all the fields, and put static ones in a map.
        Field[] fields = type.getDeclaredFields();

        for (Field field : fields) {
            // Check to see if this is public static final. If not, it's not a constant.
            int modifiers = field.getModifiers();
            if (!Modifier.isFinal(modifiers) || !Modifier.isStatic(modifiers) || !Modifier.isPublic(modifiers)) {
                continue;
            }

            try {
                Object value = field.get(null); // null for static fields.
                constants.put(field.getName(), value);
            }
            catch (Exception e) {
                throw new FacesException("Could not get value of " + field.getName() + " in " + type.getName() + ".", e);
            }
        }

        return constants;
    }
}