注：CSDN的博客在审核中 图片和排版可以等审核过了去http://blog.csdn.net/zyb2017/article/details/78080386查看
最近看了一些Mybatis的执行，很多不是很懂，将看到的大概写给自己零散的记录一下，一些具体分析放在以后整理整合。
# 执行流程图
网上有很多的执行流程图，个人认为比较明确的是这个：
觉得大概可以分为四部分：
1. 参数语句的传入
2. Myabtis中读取配置文件，执行器的选择，Statement的调用
3. 对数据库进行访问
4. 将输出对象返回
本文对第二步进行简单概述
# 如何生成执行语句的statement？
1.首先Mybatis要通过默认的sql会话获取Mapper，通过调用configuration的getMapper方法
```
@Override
public T getMapper(Class type) {
return configuration.getMapper(type, this);
}
```
2.configuration调用mapperRegistry.getMapper
```
public T getMapper(Class type, SqlSession sqlSession) {
return mapperRegistry.getMapper(type, sqlSession);
}
```
3.MapperRegistry获取Mapper
```
@SuppressWarnings("unchecked")
public T getMapper(Class type, SqlSession sqlSession) {
final MapperProxyFactory mapperProxyFactory = (MapperProxyFactory) knownMappers.get(type);
if (mapperProxyFactory == null) {
throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
}
try {
return mapperProxyFactory.newInstance(sqlSession);
} catch (Exception e) {
throw new BindingException("Error getting mapper instance. Cause: " + e, e);
}
}
```
mapper代理工厂将sql会话传入，new一个新的实例，那代理工厂是如何去new的呢？
4.MapperProxyFactory的执行
通过反射新建了代理工厂，用来动态的代理dao
这里不是很懂，源码中用了@SuppressWarnings注解来抑制编译器的警告信息
```
@SuppressWarnings("unchecked")
protected T newInstance(MapperProxy mapperProxy) {
return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
}
```
```
public T newInstance(SqlSession sqlSession) {
final MapperProxy mapperProxy = new MapperProxy(sqlSession, mapperInterface, methodCache);
return newInstance(mapperProxy);
}
```
5.Mapper代理的执行
```
public class MapperProxy implements InvocationHandler, Serializable {
private static final long serialVersionUID = -6424540398559729838L;
private final SqlSession sqlSession;
private final Class mapperInterface;
private final Map methodCache;
public MapperProxy(SqlSession sqlSession, Class mapperInterface, Map methodCache) {
this.sqlSession = sqlSession;
this.mapperInterface = mapperInterface;
this.methodCache = methodCache;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if (Object.class.equals(method.getDeclaringClass())) {
try {
return method.invoke(this, args);
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
}
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, method, sqlSession.getConfiguration());
methodCache.put(method, mapperMethod);
}
return mapperMethod;
}
}
```
抛去其他，可以看到其实是mapperMethod在执行，调用execute
6.来到execute，选择相应的要执行的操作，增删改查
```
public Object execute(SqlSession sqlSession, Object[] args) {
Object result;
if (SqlCommandType.INSERT == command.getType()) {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.insert(command.getName(), param));
} else if (SqlCommandType.UPDATE == command.getType()) {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.update(command.getName(), param));
} else if (SqlCommandType.DELETE == command.getType()) {
Object param = method.convertArgsToSqlCommandParam(args);
result = rowCountResult(sqlSession.delete(command.getName(), param));
} else if (SqlCommandType.SELECT == command.getType()) {
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);
}
} else if (SqlCommandType.FLUSH == command.getType()) {
result = sqlSession.flushStatements();
} else {
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;
}
```
根据选择的不同去执行sqlsession中的不同方法，然后调用executor去具体处理
再此处记录一下：executor接口 ，Statement封装 ，sql的具体执行过程
Mybatis的执行经过简述
转载于:https://my.oschina.net/u/3545445/blog/1542600