Mybatis的执行经过简述

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