Mybatis深入剖解 - typeHandlerRegistry parameterHandler resultSetHandler

Statement在具体orm的过程总，主要靠这三个类进行参数装配，结果装配和相应的类型转换

• parameterHandler
• resultSetHandler
• typeHandlerRegistry

  protected BaseStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) {    this.configuration = mappedStatement.getConfiguration();    this.executor = executor;    this.mappedStatement = mappedStatement;    this.rowBounds = rowBounds;    this.typeHandlerRegistry = configuration.getTypeHandlerRegistry();    this.objectFactory = configuration.getObjectFactory();    this.boundSql = mappedStatement.getBoundSql(parameterObject);    this.parameterHandler = configuration.newParameterHandler(mappedStatement, parameterObject, boundSql);    this.resultSetHandler = configuration.newResultSetHandler(executor, mappedStatement, rowBounds, parameterHandler, resultHandler, boundSql);  }

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parameterHandler

? ? 只有一个实现类，DefaultParameterHandler，它负责把代码传入的参数，装配到preparestatement中去，根据下面的代码可以看出，根据mapper中配置的解析出的parameterMapping规则从代码传入parameterObject的对象出反射取出属性值，在根据TypeHandler做java到jdbc类型的数据格式转换，最终装配到jdbc的statement中去

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  MetaObject metaObject = parameterObject == null ? null : configuration.newMetaObject(parameterObject);      for (int i = 0; i < parameterMappings.size(); i++) {        ParameterMapping parameterMapping = parameterMappings.get(i);        if (parameterMapping.getMode() != ParameterMode.OUT) {          Object value;          String propertyName = parameterMapping.getProperty();          PropertyTokenizer prop = new PropertyTokenizer(propertyName);          if (parameterObject == null) {            value = null;          } else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {            value = parameterObject;          } else if (boundSql.hasAdditionalParameter(propertyName)) {            value = boundSql.getAdditionalParameter(propertyName);          } else if (propertyName.startsWith(ForEachSqlNode.ITEM_PREFIX)              && boundSql.hasAdditionalParameter(prop.getName())) {            value = boundSql.getAdditionalParameter(prop.getName());            if (value != null) {              value = configuration.newMetaObject(value).getValue(propertyName.substring(prop.getName().length()));            }          } else {            value = metaObject == null ? null : metaObject.getValue(propertyName);          }          TypeHandler typeHandler = parameterMapping.getTypeHandler();          if (typeHandler == null) {            throw new ExecutorException("There was no TypeHandler found for parameter " + propertyName + " of statement " + mappedStatement.getId());          }          typeHandler.setParameter(ps, i + 1, value, parameterMapping.getJdbcType());        }

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resultSetHandler

?有两个实现，一般结果集处理由FastResultSetHandler完成，嵌套符合结果集的处理由NestedResultSetHandler完成，看下面的resultset的配置就能明白是啥意思了

ResultSetHandler resultSetHandler = mappedStatement.hasNestedResultMaps() ? new NestedResultSetHandler(executor, mappedStatement, parameterHandler, resultHandler, boundSql,        rowBounds) : new FastResultSetHandler(executor, mappedStatement, parameterHandler, resultHandler, boundSql, rowBounds);

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<resultMap id="processDefinitionResultMap"          type="com.apusic.bpm.engine.definition.ProcessDefinition">          <constructor>              <idArg column="ID_" jdbcType="VARCHAR" javaType="java.lang.String" />              <arg column="KEY_" jdbcType="VARCHAR" javaType="java.lang.String" />              <arg column="NAME_" jdbcType="VARCHAR" javaType="java.lang.String" />              <arg column="VERSION_" jdbcType="INTEGER" javaType="java.lang.Long" />              <arg column="DESCRIPTION_" jdbcType="VARCHAR" javaType="java.lang.String" />              <arg javaType="com.apusic.bpm.engine.definition.ProcessDefinitionResourceMapping" resultMap="resourceMappingResultMap" />          </constructor>      </resultMap>            <resultMap id="resourceMappingResultMap"          type="com.apusic.bpm.engine.definition.ProcessDefinitionResourceMapping">          <constructor>              <arg column="PROCESS_DEFINITION_PATH_" jdbcType="VARCHAR" javaType="java.lang.String"/>              <arg column="RESOURCE_PATHS_" jdbcType="VARCHAR" javaType="java.util.Set" />          </constructor>      </resultMap>  

?FastResultSetHandler的核心代码如下，从jdbc resultset结果集中去除结果，根据TypeHandler将jdbc类型的数据转换成java类型的数据，塞回到结果集java对象中

public List handleResultSets(Statement stmt) throws SQLException {    final List multipleResults = new ArrayList();    final List<ResultMap> resultMaps = mappedStatement.getResultMaps();    int resultMapCount = resultMaps.size();    int resultSetCount = 0;    ResultSet rs = stmt.getResultSet();    while (rs == null) {      // move forward to get the first resultset in case the driver      // doesn't return the resultset as the first result (HSQLDB 2.1)      if (stmt.getMoreResults()) {        rs = stmt.getResultSet();      } else {        if (stmt.getUpdateCount() == -1) {          // no more results.  Must be no resultset          break;        }      }    }    validateResultMapsCount(rs, resultMapCount);    while (rs != null && resultMapCount > resultSetCount) {      final ResultMap resultMap = resultMaps.get(resultSetCount);      handleResultSet(rs, resultMap, multipleResults);      rs = getNextResultSet(stmt);      cleanUpAfterHandlingResultSet();      resultSetCount++;    }    return collapseSingleResultList(multipleResults);  }

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