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package com.redis.riot.file.xml;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.batch.item.ItemStreamReader;
import org.springframework.batch.item.file.ResourceAwareItemReaderItemStream;
import org.springframework.batch.item.support.AbstractItemCountingItemStreamItemReader;
import org.springframework.core.io.Resource;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

/**
 * {@link ItemStreamReader} implementation that reads XML objects from a {@link Resource} having the following format:
 * 
 *  * {@code
 * 
 *    ...
 *    ...
 * 
 * }
 * 
 * 
 * The implementation is not thread-safe.
 *
 * @param  the type of XML objects to read
 *
 * @author Julien Ruaux
 */
public class XmlItemReader extends AbstractItemCountingItemStreamItemReader
        implements ResourceAwareItemReaderItemStream {

    private final Logger log = LoggerFactory.getLogger(XmlItemReader.class);

    private Resource resource;

    private XmlObjectReader xmlObjectReader;

    private boolean strict = true;

    /**
     * Create a new {@link XmlItemReader} instance.
     * 
     * @param resource the input XML resource
     * @param xmlObjectReader the XML object reader to use
     */
    public XmlItemReader(Resource resource, XmlObjectReader xmlObjectReader) {
        Assert.notNull(resource, "The resource must not be null.");
        Assert.notNull(xmlObjectReader, "The XML object reader must not be null.");
        this.resource = resource;
        this.xmlObjectReader = xmlObjectReader;
    }

    /**
     * Set the {@link XmlObjectReader} to use to read and map XML elements to domain objects.
     * 
     * @param xmlObjectReader the XML object reader to use
     */
    public void setXmlObjectReader(XmlObjectReader xmlObjectReader) {
        this.xmlObjectReader = xmlObjectReader;
    }

    /**
     * In strict mode the reader will throw an exception on {@link #open(org.springframework.batch.item.ExecutionContext)} if
     * the input resource does not exist.
     * 
     * @param strict true by default
     */
    public void setStrict(boolean strict) {
        this.strict = strict;
    }

    @Override
    public void setResource(Resource resource) {
        this.resource = resource;
    }

    @Nullable
    @Override
    protected T doRead() throws Exception {
        return xmlObjectReader.read();
    }

    @Override
    protected void doOpen() throws Exception {
        if (!this.resource.exists()) {
            if (this.strict) {
                throw new IllegalStateException("Input resource must exist (reader is in 'strict' mode)");
            }
            log.warn("Input resource does not exist: {}", resource.getDescription());
            return;
        }
        if (!this.resource.isReadable()) {
            if (this.strict) {
                throw new IllegalStateException("Input resource must be readable (reader is in 'strict' mode)");
            }
            log.warn("Input resource is not readable: {}", resource.getDescription());
            return;
        }
        this.xmlObjectReader.open(this.resource);
    }

    @Override
    protected void doClose() throws Exception {
        this.xmlObjectReader.close();
    }

}