sequenceservice.java

来自「一个很好的开源项目管理系统源代码」· Java 代码 · 共 94 行

/*

 */
package net.java.workeffort.service;

import java.util.HashMap;
import java.util.Map;

import net.java.workeffort.service.support.OptimisticLockingException;


/**
 * The sequence service.
 * <p>
 * The update of the sequence table will happen in a new transaction seperate
 * from that of the business transaction. This is configured in spring using the
 * transaction attribute <code>PROPAGATION_REQUIRES_NEW</code>
 * </p>
 * <p>
 * Note: There has to be an entry for each sequence in the
 * <code>SEQUENCE_TABLE</code>
 * </p>
 * Designed to work in a clustered environment.
 * @author Antony Joseph
 */
public class SequenceService extends BaseService implements ISequenceService {
    private int maximumTries = 10; // default. Can be set using spring.

    /**
     * Get the nextid for the sequence block
     * @param name The sequence name
     * @param blockSize The block size of the sequence
     * @return The next id
     */
    public Long getNextBlockSequenceId(String name, Integer blockSize) {
        // Need to loop for clustered environments where requests for the
        // same sequence may come from multiple cluster nodes and collide
        // causing an OptimisticLockingException.
        // (Synchronizing will not protect us here because calls are from
        // different jvms).
        // Try maximumTries times before throwing exception.
        int loopCnt = 0;
        Map sequence = null;
        while (loopCnt < maximumTries) {
            sequence = (Map) dao.queryForObject("Sequence.getSequence", name);
            if (sequence == null)
                throw new IllegalArgumentException("Sequence with name " + name
                        + " not found. Check for entry in SEQUENCE_TABLE.");
            Integer newVersion = new Integer(
                    ((Integer) sequence.get("version")).intValue() + 1);
            Long newNextId = new Long(((Long) sequence.get("nextId"))
                    .longValue()
                    + blockSize.intValue() + 1);

            Map map = new HashMap();
            map.put("nextId", newNextId);
            map.put("name", name);
            map.put("newVersion", newVersion);
            map.put("version", sequence.get("version"));

            try {
                dao.update("Sequence.updateSequence", map, false);
                break;
            }
            catch (OptimisticLockingException e) {
                // keep looping if the update was not successful.
            }

            loopCnt++;
        }

        if (loopCnt < maximumTries)
            return (Long) sequence.get("nextId");
        else {
            throw new RuntimeException("Failed to get sequence for " + name
                    + " after " + maximumTries + " tries.");
        }
    }

    /**
     * @return Returns the maximumTries.
     */
    public int getMaximumTries() {
        return maximumTries;
    }

    /**
     * @param maximumTries The maximumTries to set. Can be set by spring IOC
     */
    public void setMaximumTries(int maximumTries) {
        this.maximumTries = maximumTries;
    }

}