mybatis热部署加载*Mapper.xml文件

需求：mybatis的sql文件暴露在外面，但是当我们修改了对应的mapper.xml文件后，怎样才能避免重启项目实现热加载这类配置文件呢？
环境：springMVC(其中spring3.1.1、mybatis3.2.1)

1.首先看一下mybatis映射层目录结构图如下（Users.java是实体类、SqlMapConfig.xml是管理加载所有的mapper.xml文件、Users.xml是mapper.xml文件）：

Users.java内容如下：

package com.pingpeng.misp.models;

public class Users implements java.io.Serializable {

	private static final long serialVersionUID = -6057344509602820411L;
	private Integer id;
	private Integer enable;
	private String password;
	private String account;
	
	// 四个属性的get、set方法请自行添加,此处不写了
	
}

SqlMapConfig.xml内容如下：

Users.xml内容如下：

 


	
	
		select * from users where account = #{account}
	
	
		select * from users 
	

2.再看看application.xml中关于mabatis的配置(什么数据源之类的就不贴出来了)：

 

3.最后看看com.pingpeng.misp.common.SqlSessionCache这个缓存类refreshMapper方法是如何实现刷新的：

package com.pingpeng.misp.common;

import java.io.IOException;
import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.ibatis.builder.xml.XMLMapperBuilder;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.SqlSessionFactory;
import org.springframework.core.io.Resource;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;

public class SqlSessionCache {
	private Log log  = LogFactory.getLog(SqlSessionCache.class);
	
	private SqlSessionFactory sqlSessionFactory;
	private Resource[] mapperLocations;
	private String packageSearchPath;
	private HashMap fileMapping = new HashMap();// 记录文件是否变化
	
	public void refreshMapper() {
		try {
			Configuration configuration = this.sqlSessionFactory.getConfiguration();
			
			// step.1 扫描文件
			try {
				this.scanMapperXml();
			} catch (IOException e) {
				log.error("packageSearchPath扫描包路径配置错误");
				return;
			}
			
			System.out.println("==============刷新前mapper中的内容===============");
			for (String name : configuration.getMappedStatementNames()) {
				System.out.println(name);
			}
			
			// step.2 判断是否有文件发生了变化
			if (this.isChanged()) {
				// step.2.1 清理
				this.removeConfig(configuration);

				// step.2.2 重新加载
				for (Resource configLocation : mapperLocations) {
					try {
						XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(configLocation.getInputStream(), configuration, configLocation.toString(), configuration.getSqlFragments());
						xmlMapperBuilder.parse();
						log.info("mapper文件[" + configLocation.getFilename() + "]缓存加载成功");
					} catch (IOException e) {
						log.error("mapper文件[" + configLocation.getFilename() + "]不存在或内容格式不对");
						continue;
					}
				}
			}
			
			System.out.println("==============刷新后mapper中的内容===============");
			for (String name : configuration.getMappedStatementNames()) {
				System.out.println(name);
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	public void setPackageSearchPath(String packageSearchPath) {
		this.packageSearchPath = packageSearchPath;
	}
	
	public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) {
		this.sqlSessionFactory = sqlSessionFactory;
	}

	/**
	 * 扫描xml文件所在的路径
	 * @throws IOException 
	 */
	private void scanMapperXml() throws IOException {
		this.mapperLocations = new PathMatchingResourcePatternResolver().getResources(packageSearchPath);
	}

	/**
	 * 清空Configuration中几个重要的缓存
	 * @param configuration
	 * @throws Exception
	 */
	private void removeConfig(Configuration configuration) throws Exception {
		Class classConfig = configuration.getClass();
		clearMap(classConfig, configuration, "mappedStatements");
		clearMap(classConfig, configuration, "caches");
		clearMap(classConfig, configuration, "resultMaps");
		clearMap(classConfig, configuration, "parameterMaps");
		clearMap(classConfig, configuration, "keyGenerators");
		clearMap(classConfig, configuration, "sqlFragments");

		clearSet(classConfig, configuration, "loadedResources");

	}

	@SuppressWarnings("rawtypes")
	private void clearMap(Class classConfig, Configuration configuration, String fieldName) throws Exception {
		Field field = classConfig.getDeclaredField(fieldName);
		field.setAccessible(true);
		Map mapConfig = (Map) field.get(configuration);
		mapConfig.clear();
	}

	@SuppressWarnings("rawtypes")
	private void clearSet(Class classConfig, Configuration configuration, String fieldName) throws Exception {
		Field field = classConfig.getDeclaredField(fieldName);
		field.setAccessible(true);
		Set setConfig = (Set) field.get(configuration);
		setConfig.clear();
	}
	
	/**
	 * 判断文件是否发生了变化
	 * @param resource
	 * @return
	 * @throws IOException
	 */
	private boolean isChanged() throws IOException {
		boolean flag = false;
		for (Resource resource : mapperLocations) {
			String resourceName = resource.getFilename();
			
			boolean addFlag = !fileMapping.containsKey(resourceName);// 此为新增标识
			
			// 修改文件:判断文件内容是否有变化
			Long compareFrame = fileMapping.get(resourceName);
			long lastFrame = resource.contentLength() + resource.lastModified();
			boolean modifyFlag = null != compareFrame && compareFrame.longValue() != lastFrame;// 此为修改标识
			
			// 新增或是修改时,存储文件
			if(addFlag || modifyFlag) {
				fileMapping.put(resourceName, Long.valueOf(lastFrame));// 文件内容帧值
				flag = true;
			}
		}
		return flag;
	}
}

总结：

1.可以写个定时器每隔一段时间执行SqlSessionCache中refreshMapper()方法，这样就实现热部署功能

2.注意配置的路径一定要是所有的mapper映射文件，而不是总管理文件

3.当前实现如果只改动了一个文件，那么也只重新加载所有文件，如何实现只加载更新的文件呢，这个有点复杂，请自行研究