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    • org.thymeleaf.engine.DataDrivenTemplateIterator Maven / Gradle / Ivy

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    Modern server-side Java template engine for both web and standalone environments

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    /*
 * =============================================================================
 *
 *   Copyright (c) 2011-2018, The THYMELEAF team (http://www.thymeleaf.org)
 *
 *   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.thymeleaf.engine;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;

import org.thymeleaf.exceptions.TemplateProcessingException;

/**
 * 
    
 *   Throttled implementation of {@link Iterator}, meant to be queried in scenarios when an iterated
 *   context variable is allowed to be in control of the engine's throttling (i.e. the engine's execution
 *   is data-driven).
 * 
    
 * 
    
 *   A common scenario for this would be reactive systems executing the template engine as a part of a
 *   flow obtaining data from a data source, so that as the data is obtained, a part of the template is output
 *   containing that part of the data.
 * 
    
 * 
    
 *   This class is meant for internal use only from the diverse integrations of Thymeleaf in
 *   reactive architectures. There is normally no reason why a user would have to use this class directly.
 * 
    
 *
 * @author Daniel Fernández
 * 
 * @since 3.0.0
 *
 */
public final class DataDrivenTemplateIterator implements Iterator {

    private static final char[] SSE_HEAD_EVENT_NAME = "head".toCharArray();
    private static final char[] SSE_MESSAGE_EVENT_NAME = "message".toCharArray();
    private static final char[] SSE_TAIL_EVENT_NAME = "tail".toCharArray();


    private final List values;
    private IThrottledTemplateWriterControl writerControl;
    private ISSEThrottledTemplateWriterControl sseControl;
    private char[] sseEventsPrefix;
    private char[] sseEventsComposedMessageEventName; // Used to cache the prefixed name of the most used type
    private long sseEventsID;
    private boolean inStep;
    private boolean feedingComplete;
    private boolean queried;


    public DataDrivenTemplateIterator() {

        super();
        this.values = new ArrayList(10);
        this.writerControl = null;
        this.sseControl = null;
        this.sseEventsPrefix = null;
        this.sseEventsComposedMessageEventName = null;
        this.sseEventsID = 0L;
        this.inStep = false;
        this.feedingComplete = false;
        this.queried = false;

    }


    public void setWriterControl(final IThrottledTemplateWriterControl writerControl) {
        this.writerControl = writerControl;
        if (writerControl instanceof ISSEThrottledTemplateWriterControl) {
            this.sseControl = (ISSEThrottledTemplateWriterControl) this.writerControl;
        } else {
            this.sseControl = null;
        }
    }


    public void setSseEventsPrefix(final String sseEventsPrefix) {
        this.sseEventsPrefix =
                (sseEventsPrefix == null || sseEventsPrefix.length() == 0? null : sseEventsPrefix.toCharArray());
        this.sseEventsComposedMessageEventName = composeToken(SSE_MESSAGE_EVENT_NAME);
    }

    public void setSseEventsFirstID(final long sseEventsFirstID) {
        this.sseEventsID = sseEventsFirstID;
    }

    public void takeBackLastEventID() {
        if (this.sseEventsID > 0L) {
            this.sseEventsID--;
        }
    }


    @Override
    public boolean hasNext() {
        this.queried = true;
        return !this.values.isEmpty();
    }


    @Override
    public Object next() {

        this.queried = true;

        if (this.values.isEmpty()) {
            throw new NoSuchElementException();
        }

        final Object value = this.values.get(0);
        this.values.remove(0);
        return value;

    }


    public void startIteration() {
        this.inStep = true;
        if (this.sseControl != null) {
            final char[] id = composeToken(Long.toString(this.sseEventsID).toCharArray());
            final char[] event = this.sseEventsComposedMessageEventName;
            this.sseControl.startEvent(id, event);
            this.sseEventsID++;
        }
    }


    public void finishIteration() {
        finishStep();
    }


    /**
     * 
    
     *   Returns whether this data driven iterator has been actually queried, i.e., whether its {@link #hasNext()} or
     *   {@link #next()} methods have been called at least once.
     * 
    
     * 
    
     *   This indicates if the template has actually reached a point at which this iterator has been already
     *   needed or not. The typical use of this is to be able to switch between the "head" and the "data/buffer" phase.
     * 
    
     *
     * @return {@code true} if this iterator has been queried, {@code false} if not.
     *
     * @since 3.0.3
     */
    public boolean hasBeenQueried() {
        return this.queried;
    }


    @Override
    public void remove() {
        throw new UnsupportedOperationException("remove() is not supported in Throttled Iterator");
    }



    boolean isPaused() {
        this.queried = true;
        return this.values.isEmpty() && !this.feedingComplete;
    }


    public boolean continueBufferExecution() {
        return !this.values.isEmpty();
    }


    public void feedBuffer(final List newElements) {
        this.values.addAll(newElements);
    }



    public void startHead() {
        this.inStep = true;
        if (this.sseControl != null) {
            final char[] id = composeToken(Long.toString(this.sseEventsID).toCharArray());
            final char[] event = composeToken(SSE_HEAD_EVENT_NAME);
            this.sseControl.startEvent(id, event);
            this.sseEventsID++;
        }
    }

    public void feedingComplete() {
        this.feedingComplete = true;
    }


    public void startTail() {
        this.inStep = true;
        if (this.sseControl != null) {
            final char[] id = composeToken(Long.toString(this.sseEventsID).toCharArray());
            final char[] event = composeToken(SSE_TAIL_EVENT_NAME);
            this.sseControl.startEvent(id, event);
            this.sseEventsID++;
        }
    }


    public void finishStep() {
        if (!this.inStep) {
            return;
        }
        this.inStep = false;
        if (this.sseControl != null) {
            try {
                this.sseControl.endEvent();
            } catch (final IOException e) {
                throw new TemplateProcessingException("Cannot signal end of SSE event", e);
            }
        }
    }


    public boolean isStepOutputFinished() {
        if (this.inStep) {
            return false;
        }
        if (this.writerControl != null) {
            try {
                return !this.writerControl.isOverflown();
            } catch (final IOException e) {
                throw new TemplateProcessingException("Cannot signal end of SSE event", e);
            }
        }
        // We just don't know, so we will not worry about overflow
        return true;
    }



    private char[] composeToken(final char[] token) {
        if (this.sseEventsPrefix == null) {
            return token;
        }
        final char[] result = new char[this.sseEventsPrefix.length + 1 + token.length];
        System.arraycopy(this.sseEventsPrefix, 0, result, 0, this.sseEventsPrefix.length);
        result[this.sseEventsPrefix.length] = '_';
        System.arraycopy(token, 0, result, this.sseEventsPrefix.length + 1, token.length);
        return result;
    }

}
    
    
    
    

    




    
    
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