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);
}
typeHandlerRegistry
先介绍Typehandler,因为它是ParameterHandler和ResultsetHandler中,类型转化的工具,概括而说,typehandler就是把Java类型数据和JDBC类型的数据相互转换,mybatis给我们提供了一些常规类型的handler,我们可以自己实现一些特殊类型的handler
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
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());
}
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);
<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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