Mybatis执行过程简介

以下是使用mybatis默认设置PreparedStatement执行insert的简略时序图，省略了XMLConfigBuilder.parse()的解析细节，缓存和事务等的使用，可以和源码对照着看

XMLConfigBuilder:解析mybatis配置文件

　　XMLMapperBuilder: 解析mapper配置文件

　　　　XMLStatementBuilder: 解析SQL语句标签(此处得到SqlSource对象)

注意：

　　1. KeyGenerator的设置也是在XMLConfigBuilder.parse()过程中进行的，每个mapper文件中的每个不同id的标签(insert | update等)，可能对应的KeyGeneratior类型也不一样

　　2. 对SQL语句解析结果的存储会放到SqlSource中，最终执行的SQL语句会放到BoundSql中，对过滤条件的处理在SqlSource中的SqlNode的apply()方法执行，并通过SqlSourceBuilder.parse()来获取最终给数据库的预编译SQL语句

　　3. XMLConfigBuilder：解析mapper文件，对于类似<insert><if></if></insert>标签嵌套的标签，生成的SqlSource是一个DynamicSqlSource，里边对于SQL语句和标签保存的是SqlNode节点。其他的生成的SqlSource是RawSqlSource

　　4. 在第21步，Configuration.newStatementHandler(Executor, MappedStatement, ParamObject, RowBounds, ResultHandler, BoundSql)中会调用到BaseStatementHandler的构造函数，源码如下：

public abstract class BaseStatementHandler implements StatementHandler {

  protected final Configuration configuration;
  protected final ObjectFactory objectFactory;
  protected final TypeHandlerRegistry typeHandlerRegistry;
  protected final ResultSetHandler resultSetHandler;
  protected final ParameterHandler parameterHandler;

  protected final Executor executor;
  protected final MappedStatement mappedStatement;
  protected final RowBounds rowBounds;

  protected BoundSql boundSql;

  protected BaseStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
    this.configuration = mappedStatement.getConfiguration();
    this.executor = executor;
    this.mappedStatement = mappedStatement;
    this.rowBounds = rowBounds;

    this.typeHandlerRegistry = configuration.getTypeHandlerRegistry();
    this.objectFactory = configuration.getObjectFactory();

    if (boundSql == null) { // issue #435, get the key before calculating the statement
      generateKeys(parameterObject);
      boundSql = mappedStatement.getBoundSql(parameterObject); //此处会转换动态SQL语句，根据传递的参数和判断条件，得出最终的SQL语句(拥有占位符)
    }

    this.boundSql = boundSql;

    this.parameterHandler = configuration.newParameterHandler(mappedStatement, parameterObject, boundSql);
    this.resultSetHandler = configuration.newResultSetHandler(executor, mappedStatement, rowBounds, parameterHandler, resultHandler, boundSql);
  }
}

public final class MappedStatement {
 public BoundSql getBoundSql(Object parameterObject) {
    BoundSql boundSql = sqlSource.getBoundSql(parameterObject);
    List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
    if (parameterMappings == null || parameterMappings.size() <= 0) {
      boundSql = new BoundSql(configuration, boundSql.getSql(), parameterMap.getParameterMappings(), parameterObject);
    }

    // check for nested result maps in parameter mappings (issue #30)
    for (ParameterMapping pm : boundSql.getParameterMappings()) {
      String rmId = pm.getResultMapId();
      if (rmId != null) {
        ResultMap rm = configuration.getResultMap(rmId);
        if (rm != null) {
          hasNestedResultMaps |= rm.hasNestedResultMaps();
        }
      }
    }

    return boundSql;
  }
}

public class DynamicSqlSource implements SqlSource {

　　　　private Configuration configuration;
　　　　private SqlNode rootSqlNode;

 public BoundSql getBoundSql(Object parameterObject) {
    DynamicContext context = new DynamicContext(configuration, parameterObject);
    rootSqlNode.apply(context);
    SqlSourceBuilder sqlSourceParser = new SqlSourceBuilder(configuration);
    Class<?> parameterType = parameterObject == null ? Object.class : parameterObject.getClass();
    SqlSource sqlSource = sqlSourceParser.parse(context.getSql(), parameterType, context.getBindings());
    BoundSql boundSql = sqlSource.getBoundSql(parameterObject);
    for (Map.Entry<String, Object> entry : context.getBindings().entrySet()) {
      boundSql.setAdditionalParameter(entry.getKey(), entry.getValue());
    }
    return boundSql;
  }
}

 

总结：

　　XMLConfigBuilder知识对mapper.xml做解析，并保存解析的结果，解析的结果可能是静态SQL(没有过滤条件，就一条原生SQL语句(包含占位符))，也可能是动态SQL(拥有过滤条件，需要在执行的时候根据参数来过滤)

　　等到真正开始执行的时候(第21步(创建StatementHandler))时，才会根据传入的参数对过滤条件进行处理，得到最终要预处理的SQL语句(包含占位符):

　　　　这一步包含两个最重要的步骤：1. 处理mybatis提供的SqlNode(if，foreach，where，set等)  2. 使用占位符?替换掉固定格式#{xx}