DistributedLockServiceMySqlImpl.java

package com.aol.micro.server.mysql.distlock;

import javax.sql.DataSource;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.stereotype.Component;

import com.aol.micro.server.dist.lock.DistributedLockService;

@Component
public class DistributedLockServiceMySqlImpl implements DistributedLockService {

    static final String GET_LOCK_TEMPLATE = "select COALESCE(GET_LOCK(?, 0), 0)";
    static final String RELEASE_LOCK_TEMPLATE = "select COALESCE(RELEASE_LOCK(?), 0)";

    volatile JdbcTemplate jdbcTemplate;

    @Autowired(required = false)
    @Qualifier("distLockingDataSource")
    public void setSmartDataSource(DataSource dataSource) {
        if (dataSource != null)
            this.jdbcTemplate = new JdbcTemplate(
                                                 dataSource);
    }

    @Override
    public boolean tryLock(String key) {
        return executeScalar(GET_LOCK_TEMPLATE, key, 1);
    }

    @Override
    public boolean tryReleaseLock(String key) {
        return executeScalar(RELEASE_LOCK_TEMPLATE, key, 1);
    }

    synchronized boolean executeScalar(String operation, String key, Integer expectedResult) {

        int result = jdbcTemplate.queryForObject(operation, new Object[] { key }, Integer.class);
        return result == expectedResult;

    }

    public void setJdbcTemplate(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }

}