Mybatis之工作原理

1.Mybatis的架构

1.1 Mybatis的框架分层

这里写图片描述

1.2 MyBatis的实现原理

mybatis底层还是采用原生jdbc来对数据库进行操作的，只是通过 SqlSessionFactory，SqlSession Executor,StatementHandler，ParameterHandler,ResultHandler和TypeHandler等几个处理器封装了这些过程

 执行器：Executor (update, query, flushStatements, commit, rollback, getTransaction, close, isClosed) 参数处理器： ParameterHandler (getParameterObject, setParameters) 结构处理器 ResultSetHandler (handleResultSets, handleOutputParameters) sql查询处理器：StatementHandler (prepare, parameterize, batch, update, query)

2.Mybatis工作过程

2.1 创建SqlSessionFacotry的过程

从debug调试看出返回的 sqlSessionFactory 是DefaultSesssionFactory类型的，但是configuration此时已经被初始化了。查看源码后画如下创建DefaultSessionFactory的时序图：
这里写图片描述

2.2 创建SqlSession的过程

这里写图片描述
从debug调试看出SqlSessinoFactory.openSession() 返回的sqlSession是 DefaultSession类型的，此SqlSession里包含一个Configuration的对象，和一个Executor对象。查看源码后画如下创建DefaultSession的时序图：

这里写图片描述

2.3 创建Mapper的过程

从debug调试可以看出，mapper是一个Mapper代理对象，而且初始化了Configuration对象，Executor的对象。查看源码后画如下创建Mapper的时序图：
这里写图片描述

2.4 执行CRUD过程

2.4.1 以select为例查看各步执行的源码

1.mapper.selectEmployeeList()其实是MapperProxy执行invoke方法，此方法显示是判断Method的方法是不是Object的toString等方法如果不是就执行MapperMethod

 public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { // 判断Method的方法是不是Object的toString等方法  if(Object.class.equals(method.getDeclaringClass())) { try { return method.invoke(this, args); } catch (Throwable var5) { throw ExceptionUtil.unwrapThrowable(var5); } } else { //判断private final Map 
   
     methodCache;这个map里面有没有这个方法的一级缓存，如果没 
    MapperMethod mapperMethod = this.cachedMapperMethod(method); return mapperMethod.execute(this.sqlSession, args); } } //查询一级缓存和设置一级缓存 private MapperMethod cachedMapperMethod(Method method) { MapperMethod mapperMethod = (MapperMethod)this.methodCache.get(method); if(mapperMethod == null) { mapperMethod = new MapperMethod(this.mapperInterface, method, this.sqlSession.getConfiguration()); this.methodCache.put(method, mapperMethod); } return mapperMethod; }

经过上面的调用后进入MapperMethod里面执行

//判断sql命令类型 public Object execute(SqlSession sqlSession, Object[] args) { Object param; Object result; if(SqlCommandType.INSERT == this.command.getType()) { param = this.method.convertArgsToSqlCommandParam(args); result = this.rowCountResult(sqlSession.insert(this.command.getName(), param)); } else if(SqlCommandType.UPDATE == this.command.getType()) { param = this.method.convertArgsToSqlCommandParam(args); result = this.rowCountResult(sqlSession.update(this.command.getName(), param)); } else if(SqlCommandType.DELETE == this.command.getType()) { param = this.method.convertArgsToSqlCommandParam(args); result = this.rowCountResult(sqlSession.delete(this.command.getName(), param)); } else if(SqlCommandType.SELECT == this.command.getType()) { //我们测试的是select类型，则再判断这个方法的返回类型 if(this.method.returnsVoid() && this.method.hasResultHandler()) { this.executeWithResultHandler(sqlSession, args); result = null; } else if(this.method.returnsMany()) { //我们是查询列表，此方法执行 result = this.executeForMany(sqlSession, args); } else if(this.method.returnsMap()) { result = this.executeForMap(sqlSession, args); } else { param = this.method.convertArgsToSqlCommandParam(args); result = sqlSession.selectOne(this.command.getName(), param); } } else { if(SqlCommandType.FLUSH != this.command.getType()) { throw new BindingException("Unknown execution method for: " + this.command.getName()); } result = sqlSession.flushStatements(); } if(result == null && this.method.getReturnType().isPrimitive() && !this.method.returnsVoid()) { throw new BindingException("Mapper method '" + this.command.getName() + " attempted to return null from a method with a primitive return type (" + this.method.getReturnType() + ")."); } else { return result; } } private 
  
    Object executeForMany(SqlSession sqlSession, Object[] args) { //将param做处理 自动处理为param1,param2.. Object param = this 
   .method 
   .convertArgsToSqlCommandParam(args) 
   ; List result 
   ; if(this 
   .method 
   .hasRowBounds()) { RowBounds rowBounds = this 
   .method 
   .extractRowBounds(args) 
   ; //调用该对象的DefaultSqlSession的selectList方法 result = sqlSession 
   .selectList(this 
   .command 
   .getName(), param, rowBounds) 
   ; } else { result = sqlSession 
   .selectList(this 
   .command 
   .getName(), param) 
   ; } return !this 
   .method 
   .getReturnType() 
   .isAssignableFrom(result 
   .getClass())?(this 
   .method 
   .getReturnType() 
   .isArray()?this 
   .convertToArray(result):this 
   .convertToDeclaredCollection(sqlSession 
   .getConfiguration(), result)):result 
   ; } //处理参数方法 public Object convertArgsToSqlCommandParam(Object[] args) { int paramCount = this 
   .params 
   .size() 
   ; if(args != null && paramCount != 
   0) { if(!this 
   .hasNamedParameters && paramCount == 
   1) { return args[((Integer)this 
   .params 
   .keySet() 
   .iterator() 
   .next()) 
   .intValue()] 
   ; } else { Map 
   
     param = new MapperMethod 
    .ParamMap() 
    ; int i = 
    0 
    ; for(Iterator i$ = this 
    .params 
    .entrySet() 
    .iterator() 
    ; i$.hasNext(); ++i) { 
      Entry 
    
      entry = (Entry)i$ 
     .next() 
     ; param 
     .put(entry 
     .getValue(), args[((Integer)entry 
     .getKey()) 
     .intValue()]) 
     ; String genericParamName = 
     "param" + String 
     .valueOf(i + 
     1) 
     ; if(!param 
     .containsKey(genericParamName)) { param 
     .put(genericParamName, args[((Integer)entry 
     .getKey()) 
     .intValue()]) 
     ; } } return param 
     ; } } else { return null 
     ; } }

调用DefaultSqlSession的selectList的方法

 public 
  
    List 
    
    selectList(String statement, Object parameter, RowBounds rowBounds) { List var5; 
    try { 
    //获取MappedStatement对象 MappedStatement ms = 
    this.configuration.getMappedStatement(statement); 
    //调用cachingExecutor执行器的方法 var5 = 
    this.executor.query(ms, 
    this.wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER); } 
    catch (Exception var9) { 
    throw ExceptionFactory.wrapException( 
    "Error querying database. Cause: " + var9, var9); } 
    finally { ErrorContext.instance().reset(); } 
    return var5; } 
    //CachingExector的query方法 
    public 
    
      List 
      
      query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException { 
      // BoundSql boundSql = ms.getBoundSql(parameterObject); CacheKey key = 
      this.createCacheKey(ms, parameterObject, rowBounds, boundSql); 
      //调用下2代码 
      return 
      this.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); } 
      //2代码 
      public 
      
        List 
        
        query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException { Cache cache = ms.getCache(); 
        if(cache != 
        null) { 
        this.flushCacheIfRequired(ms); 
        if(ms.isUseCache() && resultHandler == 
        null) { 
        this.ensureNoOutParams(ms, parameterObject, boundSql); List 
        
          list = (List) 
         this.tcm.getObject(cache, key); 
         if(list == 
         null) { 
         //这里是调用Executor里的query方法 如果开启了缓存这掉CachingExecutor的 如果没有则是调用BaseExecutor的 list = 
         this. 
         delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); 
         this.tcm.putObject(cache, key, list); } 
         return list; } } 
         return 
         this. 
         delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); }

BaseExecutor的query方法

public 
  
    List 
    
    query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) 
    throws SQLException { ErrorContext.instance().resource(ms.getResource()).activity( 
    "executing a query").object(ms.getId()); 
    if( 
    this.closed) { 
    throw 
    new ExecutorException( 
    "Executor was closed."); } 
    else { 
    if( 
    this.queryStack == 
    0 && ms.isFlushCacheRequired()) { 
    this.clearLocalCache(); } List list; 
    try { ++ 
    this.queryStack; list = resultHandler == 
    null?(List) 
    this.localCache.getObject(key): 
    null; 
    if(list != 
    null) { 
    this.handleLocallyCachedOutputParameters(ms, key, parameter, boundSql); } 
    else { 
    //如果缓存中没有就从数据库中查询 list = 
    this.queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql); } } 
    finally { -- 
    this.queryStack; } 
    if( 
    this.queryStack == 
    0) { Iterator i$ = 
    this.deferredLoads.iterator(); 
    while(i$.hasNext()) { BaseExecutor.DeferredLoad deferredLoad = (BaseExecutor.DeferredLoad)i$.next(); deferredLoad.load(); } 
    this.deferredLoads.clear(); 
    if( 
    this.configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) { 
    this.clearLocalCache(); } } 
    return list; } } 
    //从数据库中查询 
    private 
    
      List 
      
      queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) 
      throws SQLException { 
      //放入缓存 
      this.localCache.putObject(key, ExecutionPlaceholder.EXECUTION_PLACEHOLDER); List list; 
      try { 
      //此处是调用子Executor的方法，ExecutorType默认是使用的SimpleExecutor list = 
      this.doQuery(ms, parameter, rowBounds, resultHandler, boundSql); } 
      finally { 
      this.localCache.removeObject(key); } 
      this.localCache.putObject(key, list); 
      if(ms.getStatementType() == StatementType.CALLABLE) { 
      this.localOutputParameterCache.putObject(key, parameter); } 
      return list; }

SimpleExecutor的doQuery方法

public 
  
    List 
    
    doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) 
    throws SQLException { Statement stmt = 
    null; List var9; 
    try { Configuration configuration = ms.getConfiguration(); 
    //创建StateMentHandler处理器 StatementHandler handler = configuration.newStatementHandler( 
    this.wrapper, ms, parameter, rowBounds, resultHandler, boundSql); 
    //调用下3的方法 stmt = 
    this.prepareStatement(handler, ms.getStatementLog()); 
    //调用no4的方法 var9 = handler.query(stmt, resultHandler); } 
    finally { 
    this.closeStatement(stmt); } 
    return var9; } 
    //下3方法 
    private Statement 
    prepareStatement(StatementHandler handler, Log statementLog) 
    throws SQLException { Connection connection = 
    this.getConnection(statementLog); Statement stmt = handler.prepare(connection); 
    //SatementHanlder 采用PreparedStatementHandler来实现此方法，而PreparedStatementHandler调用的是父接口ParameterHandler的方法 handler.parameterize(stmt); 
    return stmt; }

ParameterHandler参数处理器的方法

public interface ParameterHandler { Object getParameterObject(); //此方法是用DefaultParameterHandler实现的 void setParameters(PreparedStatement var1) throws SQLException; }

DefaultParameterHandler默认参数处理器的方法

public void setParameters(PreparedStatement ps) { ErrorContext.instance().activity("setting parameters").object(this.mappedStatement.getParameterMap().getId()); List 
  
    parameterMappings = 
   this.boundSql.getParameterMappings(); 
   if(parameterMappings != 
   null) { 
   for( 
   int i = 
   0; i < parameterMappings.size(); ++i) { ParameterMapping parameterMapping = (ParameterMapping)parameterMappings. 
   get(i); 
   if(parameterMapping.getMode() != ParameterMode.OUT) { String propertyName = parameterMapping.getProperty(); Object 
   value; 
   if( 
   this.boundSql.hasAdditionalParameter(propertyName)) { 
   value = 
   this.boundSql.getAdditionalParameter(propertyName); } 
   else 
   if( 
   this.parameterObject == 
   null) { 
   value = 
   null; } 
   else 
   if( 
   this.typeHandlerRegistry.hasTypeHandler( 
   this.parameterObject.getClass())) { 
   value = 
   this.parameterObject; } 
   else { MetaObject metaObject = 
   this.configuration.newMetaObject( 
   this.parameterObject); 
   value = metaObject.getValue(propertyName); } 
   //这里用调用 TypeHandler类型映射处理器来映射 TypeHandler typeHandler = parameterMapping.getTypeHandler(); JdbcType jdbcType = parameterMapping.getJdbcType(); 
   if( 
   value == 
   null && jdbcType == 
   null) { jdbcType = 
   this.configuration.getJdbcTypeForNull(); } 
   try { 
   //类型处理器设置参数映射 typeHandler.setParameter(ps, i + 
   1, 
   value, jdbcType); } 
   catch (TypeException var10) { 
   throw 
   new TypeException( 
   "Could not set parameters for mapping: " + parameterMapping + 
   ". Cause: " + var10, var10); } 
   catch (SQLException var11) { 
   throw 
   new TypeException( 
   "Could not set parameters for mapping: " + parameterMapping + 
   ". Cause: " + var11, var11); } } } } }

no4的方法

 public 
  
    List 
    
    query(Statement statement, ResultHandler resultHandler) 
    throws SQLException { 
    //此处调用原生sql的处理器 PreparedStatement ps = (PreparedStatement)statement; 
    //发出原生sql命令 ps.execute(); 
    //采用ResultHandler结果处理器对结果集封装 
    return 
    this.resultSetHandler.handleResultSets(ps); }

ResultHandler代码

public interface ResultSetHandler { 
    //此处调用的是DefaultResultSetHandler的方法 
  
    List 
   
     handleResultSets(Statement var1) 
    throws SQLException; 
    void handleOutputParameters(CallableStatement var1) 
    throws SQLException; }

DefaultResultSetHandler的方法

public List

发布者：全栈程序员-站长，转载请注明出处：https://javaforall.net/209195.html原文链接：https://javaforall.net

Mybatis之工作原理

1.Mybatis的架构

1.1 Mybatis的框架分层

1.2 MyBatis的实现原理

2.Mybatis工作过程

2.1 创建SqlSessionFacotry的过程

2.2 创建SqlSession的过程

2.3 创建Mapper的过程

2.4 执行CRUD过程

2.4.1 以select为例查看各步执行的源码

关于作者

全栈程序员-站长

发表回复

Mybatis之工作原理

1.Mybatis的架构

1.1 Mybatis的框架分层

1.2 MyBatis的实现原理

2.Mybatis工作过程

2.1 创建SqlSessionFacotry的过程

2.2 创建SqlSession的过程

2.3 创建Mapper的过程

2.4 执行CRUD过程

2.4.1 以select为例查看各步执行的源码

关于作者

全栈程序员-站长

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