概述
说来惭愧，工作5年多，才来研究这个问题。平心而论，这种实际问题比什么单例模式的几种写法有意义有价值多。真要给自己找理由的话，刚工作时用hibernate及Spring Data Jpa，后短暂使用过MyBatis，再后来使用公司自研的数据访问层框架DAL，也没用到MyBatis，再就是现在的工作，一年零3个月，遇到这个问题，忍无可忍。
这个问题就是：在使用MyBatis时，不能保证一次性写对mapper.xml文件，尤其是在有join分句时，怎么办？只能改mapper.xml文件，然后重启应用。这个过程很耗时。短则1分钟，长则2~3分钟。
题外话：
IDEA自带热更新功能，参考Java开发IDE神器IntelliJ IDEA 教程，但是这个热更新对于MyBatismapper.xml文件是不生效的。
另，JRebel（需要破解）也有很强大的热更新功能（比IDEA自带的热更新功能强，但是也会有插件版本兼容问题，参考IDEA使用插件JRebel热部署失败的问题排查），现在不用这个插件，不知道能不能更新MyBatismapper.xml文件，有待调研。
实现
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.lang3.StringUtils;
import org.apache.ibatis.builder.xml.XMLMapperBuilder;
import org.apache.ibatis.executor.ErrorContext;
import org.apache.ibatis.session.Configuration;
import org.springframework.core.NestedIOException;
import org.springframework.core.io.Resource;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.InputStream;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
/**
* @author johnny
*/
@Slf4j
public class MapperRefresh implements Runnable {
/**
* 是否启用Mapper刷新线程功能
*/
private static final boolean ENABLED = true;
/**
* 刷新启用后，是否启动了刷新线程
*/
private static boolean refresh;
/**
* Mapper实际资源路径
*/
private Set<String> location;
/**
* Mapper资源路径
*/
private final Resource[] mapperLocations;
/**
* MyBatis配置对象
*/
private final Configuration configuration;
/**
* 上一次刷新时间
*/
private Long beforeTime = 0L;
/**
* 延迟刷新秒数
*/
private static final int DELAY_SECONDS = 3;
/**
* 休眠时间
*/
private static final int SLEEP_SECONDS = 1;
/**
* xml文件夹匹配字符串，需要根据需要修改
*/
private static final String MAPPING_PATH = "mapper";
public static boolean isRefresh() {
return refresh;
}
public MapperRefresh(Resource[] mapperLocations, Configuration configuration) {
this.mapperLocations = mapperLocations;
this.configuration = configuration;
}
@Override
public void run() {
beforeTime = System.currentTimeMillis();
log.debug("[location] " + location);
log.debug("[configuration] " + configuration);
if (ENABLED) {
// 启动刷新线程
final MapperRefresh runnable = this;
new Thread(() -> {
if (location == null) {
location = Sets.newHashSet();
log.debug("MapperLocation's length:" + mapperLocations.length);
for (Resource mapperLocation : mapperLocations) {
String s = mapperLocation.toString().replaceAll("\\\\", "/");
s = s.substring("file [".length(), s.lastIndexOf(MAPPING_PATH) + MAPPING_PATH.length());
if (!location.contains(s)) {
location.add(s);
log.debug("Location:" + s);
}
}
log.debug("location's size:" + location.size());
}
try {
Thread.sleep(DELAY_SECONDS * 1000);
} catch (InterruptedException e) {
log.error("run error: " + e.getMessage());
}
refresh = true;
while (true) {
try {
for (String s : location) {
runnable.refresh(s, beforeTime);
}
} catch (Exception e) {
log.error("run error: " + e.getMessage());
}
try {
Thread.sleep(SLEEP_SECONDS * 1000);
} catch (InterruptedException e) {
log.error("run error: " + e.getMessage());
}
}
}, "MyBatis-Mapper-Refresh").start();
}
}
/**
* 执行刷新
*
* @param filePath 刷新目录
* @param beforeTime 上次刷新时间
*/
@SuppressWarnings({"rawtypes", "unchecked"})
private void refresh(String filePath, Long beforeTime) throws FileNotFoundException, NestedIOException {
// 本次刷新时间
long refreshTime = System.currentTimeMillis();
// 获取需要刷新的Mapper文件列表
List<File> fileList = this.getRefreshFile(new File(filePath), beforeTime);
if (fileList.size() > 0) {
log.debug("Refresh file: " + fileList.size());
}
for (File item : fileList) {
InputStream inputStream = new FileInputStream(item);
String resource = item.getAbsolutePath();
try {
// 清理原有资源，更新为自己的StrictMap方便，增量重新加载
String[] mapFieldNames = new String[]{
"mappedStatements", "caches",
"resultMaps", "parameterMaps",
"keyGenerators", "sqlFragments"
};
for (String fieldName : mapFieldNames) {
Field field = configuration.getClass().getDeclaredField(fieldName);
field.setAccessible(true);
Map map = ((Map) field.get(configuration));
if (!(map instanceof StrictMap)) {
Map newMap = new StrictMap(StringUtils.capitalize(fieldName) + "collection");
for (Object key : map.keySet()) {
try {
newMap.put(key, map.get(key));
} catch (IllegalArgumentException ex) {
newMap.put(key, ex.getMessage());
}
}
field.set(configuration, newMap);
}
}
// 清理已加载的资源标识,方便重新加载
Field loadedResourcesField = configuration.getClass().getDeclaredField("loadedResources");
loadedResourcesField.setAccessible(true);
Set loadedResourcesSet = ((Set) loadedResourcesField.get(configuration));
loadedResourcesSet.remove(resource);
// 重新编译加载资源文件
XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(inputStream, configuration,
resource, configuration.getSqlFragments());
xmlMapperBuilder.parse();
} catch (Exception e) {
throw new NestedIOException("Failed to parse mapping resource: '" + resource + "'", e);
} finally {
ErrorContext.instance().reset();
}
if (log.isDebugEnabled()) {
log.debug("Refresh file: " + item.getAbsolutePath());
log.debug("Refresh filename: " + item.getName());
}
}
// 如果刷新文件，则修改刷新时间，否则不修改
if (fileList.size() > 0) {
this.beforeTime = refreshTime;
}
}
/**
* 获取需要刷新的文件列表
*
* @param dir 目录
* @param beforeTime 上次刷新时间
* @return 刷新文件列表
*/
private List<File> getRefreshFile(File dir, Long beforeTime) {
List<File> fileList = new ArrayList<>();
File[] files = dir.listFiles();
if (files != null) {
for (File item : files) {
if (item.isDirectory()) {
fileList.addAll(this.getRefreshFile(item, beforeTime));
} else if (item.isFile()) {
if (this.checkFile(item, beforeTime)) {
fileList.add(item);
}
} else {
log.info("Error file." + item.getName());
}
}
}
return fileList;
}
/**
* 判断文件是否需要刷新
*
* @param file 文件
* @param beforeTime 上次刷新时间
* @return 需要刷新返回true，否则返回false
*/
private boolean checkFile(File file, Long beforeTime) {
return file.lastModified() > beforeTime;
}
/**
* 重写 org.apache.ibatis.session.Configuration.StrictMap 类
* 来自 MyBatis3.4.0版本，修改 put 方法，允许反复 put更新。
*/
public static class StrictMap<V> extends HashMap<String, V> {
private final String name;
public StrictMap(String name, int initialCapacity, float loadFactor) {
super(initialCapacity, loadFactor);
this.name = name;
}
public StrictMap(String name, int initialCapacity) {
super(initialCapacity);
this.name = name;
}
public StrictMap(String name) {
super();
this.name = name;
}
public StrictMap(String name, Map<String, ? extends V> m) {
super(m);
this.name = name;
}
@Override
@SuppressWarnings("unchecked")
public V put(String key, V value) {
// ThinkGem 如果现在状态为刷新，则刷新(先删除后添加)
if (MapperRefresh.isRefresh()) {
remove(key);
}
// ThinkGem end
if (containsKey(key)) {
throw new IllegalArgumentException(name + " already contains value for " + key);
}
if (key.contains(".")) {
final String shortKey = getShortName(key);
if (super.get(shortKey) == null) {
super.put(shortKey, value);
} else {
super.put(shortKey, (V) new Ambiguity(shortKey));
}
}
return super.put(key, value);
}
@Override
public V get(Object key) {
V value = super.get(key);
if (value == null) {
throw new IllegalArgumentException(name + " does not contain value for " + key);
}
if (value instanceof Ambiguity) {
throw new IllegalArgumentException(((Ambiguity) value).getSubject() + " is ambiguous in " + name
+ " (try using the full name including the namespace, or rename one of the entries)");
}
return value;
}
private String getShortName(String key) {
final String[] keyparts = key.split("\\.");
return keyparts[keyparts.length - 1];
}
protected static class Ambiguity {
private final String subject;
public Ambiguity(String subject) {
this.subject = subject;
}
public String getSubject() {
return subject;
}
}
}
}
RootConfiguration.java
import org.apache.ibatis.session.SqlSession;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.boot.web.servlet.support.SpringBootServletInitializer;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.FilterType;
import org.springframework.core.io.Resource;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.stereotype.Controller;
import javax.annotation.PostConstruct;
import java.io.IOException;
/**
* @author johnny
*/
@Configuration
@ComponentScan(value = "com.johnny.bbb", excludeFilters = {@ComponentScan.Filter(Controller.class),
@ComponentScan.Filter(type = FilterType.ASSIGNABLE_TYPE, value = {RootConfiguration.class})})
@MapperScan("com.johnny.bbb.common.mapper")
public class RootConfiguration extends SpringBootServletInitializer {
@javax.annotation.Resource
private SqlSession sqlSession;
@Override
protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
application.registerShutdownHook(false);
return application.sources(RootConfiguration.class);
}
@PostConstruct
public void postConstruct() throws IOException {
Resource[] resources = new PathMatchingResourcePatternResolver().getResources("classpath*:mapper/**/*Mapper.xml");
new MapperRefresh(resources, sqlSession.getConfiguration()).run();
}
}
启动类WebApplication.java改造，替换掉WebApplication.class：
@EnableTransactionManagement
@EnableScheduling
@SpringBootApplication(scanBasePackages = {"com.johnny.web.*"})
@MapperScan("com.johnny.common.mapper")
public class WebApplication extends SpringBootServletInitializer {
public static void main(String[] args) {
// 改造
SpringApplication.run(RootConfiguration.class, args);
}
@Override
protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
return builder.sources(WebApplication.class);
}
}
参考
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