由 dawei
这篇文章主要介绍了MyBatis执行Sql的流程实例解析,文中通过示例代码介绍的非常详细，对大家的学习或者工作具有一定的参考学习价值,需要的朋友可以参考下
本博客着重介绍MyBatis执行Sql的流程，关于在执行过程中缓存、动态SQl生成等细节不在本博客中体现，相应内容后面再单独写博客分析吧。
还是以之前的查询作为列子：
public class UserDaoTest {
private SqlSessionFactory sqlSessionFactory;
@Before
public void setUp() throws Exception{
ClassPathResource resource = new ClassPathResource("mybatis-config.xml");
InputStream inputStream = resource.getInputStream();
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
}
@Test
public void selectUserTest(){
String id = "{0003CCCA-AEA9-4A1E-A3CC-06D884BA3906}";
SqlSession sqlSession = sqlSessionFactory.openSession();
CbondissuerMapper cbondissuerMapper = sqlSession.getMapper(CbondissuerMapper.class);
Cbondissuer cbondissuer = cbondissuerMapper.selectByPrimaryKey(id);
System.out.println(cbondissuer);
sqlSession.close();
}
}
之前提到拿到sqlSession之后就能进行各种CRUD操作了，所以我们就从sqlSession.getMapper这个方法开始分析，看下整个Sql的执行流程是怎么样的。
获取Mapper
进入sqlSession.getMapper方法，会发现调的是Configration对象的getMapper方法：
public <T> T getMapper(Class<T> type,SqlSession sqlSession) {
//mapperRegistry实质上是一个Map，里面注册了启动过程中解析的各种Mapper.xml
//mapperRegistry的key是接口的全限定名，比如com.csx.demo.spring.boot.dao.SysUserMapper
//mapperRegistry的Value是MapperProxyFactory,用于生成对应的MapperProxy（动态代理类）
return mapperRegistry.getMapper(type,sqlSession);
}
进入getMapper方法：
public <T> T getMapper(Class<T> type,SqlSession sqlSession) {
final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
//如果配置文件中没有配置相关Mapper,直接抛异常
if (mapperProxyFactory == null) {
throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
}
try {
//关键方法
return mapperProxyFactory.newInstance(sqlSession);
} catch (Exception e) {
throw new BindingException("Error getting mapper instance. Cause: " + e,e);
}
}
进入MapperProxyFactory的newInstance方法：
public class MapperProxyFactory<T> {
private final Class<T> mapperInterface;
private final Map<Method,MapperMethod> methodCache = new ConcurrentHashMap<Method,MapperMethod>();
public MapperProxyFactory(Class<T> mapperInterface) {
this.mapperInterface = mapperInterface;
}
public Class<T> getMapperInterface() {
return mapperInterface;
}
public Map<Method,MapperMethod> getMethodCache() {
return methodCache;
}
//生成Mapper接口的动态代理类MapperProxy
@SuppressWarnings("unchecked")
protected T newInstance(MapperProxy<T> mapperProxy) {
return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(),new Class[] { mapperInterface },mapperProxy);
}
public T newInstance(SqlSession sqlSession) {
final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession,mapperInterface,methodCache);
return newInstance(mapperProxy);
}
}
下面是动态代理类MapperProxy，调用Mapper接口的所有方法都会先调用到这个代理类的invoke方法（注意由于Mybatis中的Mapper接口没有实现类，所以MapperProxy这个代理对象中没有委托类，也就是说MapperProxy干了代理类和委托类的事情）。好了下面重点看下invoke方法。
//MapperProxy代理类
public class MapperProxy<T> implements InvocationHandler,Serializable {
private static final long serialVersionUID = -6424540398559729838L;
private final SqlSession sqlSession;
private final Class<T> mapperInterface;
private final Map<Method,MapperMethod> methodCache;
public MapperProxy(SqlSession sqlSession,Class<T> mapperInterface,Map<Method,MapperMethod> methodCache) {
this.sqlSession = sqlSession;
this.mapperInterface = mapperInterface;
this.methodCache = methodCache;
}
@Override
public Object invoke(Object proxy,Method method,Object[] args) throws Throwable {
try {
if (Object.class.equals(method.getDeclaringClass())) {
return method.invoke(this,args);
} else if (isDefaultMethod(method)) {
return invokeDefaultMethod(proxy,method,args);
}
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
//获取MapperMethod，并调用MapperMethod
final MapperMethod mapperMethod = cachedMapperMethod(method);
return mapperMethod.execute(sqlSession,args);
}
private MapperMethod cachedMapperMethod(Method method) {
MapperMethod mapperMethod = methodCache.get(method);
if (mapperMethod == null) {
mapperMethod = new MapperMethod(mapperInterface,sqlSession.getConfiguration());
methodCache.put(method,mapperMethod);
}
return mapperMethod;
}
@UsesJava7
private Object invokeDefaultMethod(Object proxy,Object[] args)
throws Throwable {
final Constructor<MethodHandles.Lookup> constructor = MethodHandles.Lookup.class
.getDeclaredConstructor(Class.class,int.class);
if (!constructor.isAccessible()) {
constructor.setAccessible(true);
}
final Class<?> declaringClass = method.getDeclaringClass();
return constructor
.newInstance(declaringClass,MethodHandles.Lookup.PRIVATE | MethodHandles.Lookup.PROTECTED
| MethodHandles.Lookup.PACKAGE | MethodHandles.Lookup.PUBLIC)
.unreflectSpecial(method,declaringClass).bindTo(proxy).invokeWithArguments(args);
}
/**
* Backport of java.lang.reflect.Method#isDefault()
*/
private boolean isDefaultMethod(Method method) {
return ((method.getModifiers()
& (Modifier.ABSTRACT | Modifier.PUBLIC | Modifier.STATIC)) == Modifier.PUBLIC)
&& method.getDeclaringClass().isInterface();
}
}
所以这边需要进入MapperMethod的execute方法：
public Object execute(SqlSession sqlSession,Object[] args) {
Object result;
//判断是CRUD那种方法
switch (command.getType()) {
case INSERT: {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.insert(command.getName(),param));
break;
}
case UPDATE: {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.update(command.getName(),param));
break;
}
case DELETE: {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.delete(command.getName(),param));
break;
}
case SELECT:
if (method.returnsVoid() && method.hasResultHandler()) {
executeWithResultHandler(sqlSession,args);
result = null;
} else if (method.returnsMany()) {
result = executeForMany(sqlSession,args);
} else if (method.returnsMap()) {
result = executeForMap(sqlSession,args);
} else if (method.returnsCursor()) {
result = executeForCursor(sqlSession,args);
} else {
Object param = method.convertArgsToSqlCommandParam(args);
result = sqlSession.selectOne(command.getName(),param);
}
break;
case FLUSH:
result = sqlSession.flushStatements();
break;
default:
throw new BindingException("Unknown execution method for: " + command.getName());
}
if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {
throw new BindingException("Mapper method '" + command.getName()
+ " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");
}
return result;
}
然后，通过一层一层的调用，最终会来到doQuery方法， 这儿咱们就随便找个Excutor看看doQuery方法的实现吧，我这儿选择了SimpleExecutor:
public <E> List<E> doQuery(MappedStatement ms,Object parameter,RowBounds rowBounds,ResultHandler resultHandler,BoundSql boundSql) throws SQLException {
Statement stmt = null;
try {
Configuration configuration = ms.getConfiguration();
//内部封装了ParameterHandler和ResultSetHandler
StatementHandler handler = configuration.newStatementHandler(wrapper,ms,parameter,rowBounds,resultHandler,boundSql);
stmt = prepareStatement(handler,ms.getStatementLog());
//StatementHandler封装了Statement,让 StatementHandler 去处理
return handler.<E>query(stmt,resultHandler);
} finally {
closeStatement(stmt);
}
}