mybatis-3.4.6.release.
ParementerHandler是个接口,如下List-1
List-1
public interface ParameterHandler {
Object getParameterObject();
void setParameters(PreparedStatement ps)
throws SQLException;
}
它的默认实现只有一个DefaultParameterHandler,
List-2
@Override
public void setParameters(PreparedStatement ps) {
ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());
//获取Sql语句的参数列表
List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
if (parameterMappings != null) {
//遍历参数
for (int i = 0; i < parameterMappings.size(); i++) {
ParameterMapping parameterMapping = parameterMappings.get(i);
//只处理输入参数
if (parameterMapping.getMode() != ParameterMode.OUT) {
Object value;
String propertyName = parameterMapping.getProperty();
//获取参数值
if (boundSql.hasAdditionalParameter(propertyName)) { // issue #448 ask first for additional params
value = boundSql.getAdditionalParameter(propertyName);
} else if (parameterObject == null) {
value = null;
} else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {
value = parameterObject;
} else {
//MetaObject是Mybatis用于处理对象属性的辅助类
MetaObject metaObject = configuration.newMetaObject(parameterObject);
//如果参数不是Map,也不是List,则MetaObject是BeanWrapper
//metaObject.getValue内部,通过JDK的反射获取参数的get方法,用反射的方式获取值,method.invoke(object);
value = metaObject.getValue(propertyName);
}
TypeHandler typeHandler = parameterMapping.getTypeHandler();
JdbcType jdbcType = parameterMapping.getJdbcType();
if (value == null && jdbcType == null) {
jdbcType = configuration.getJdbcTypeForNull();
}
try {
//内部实现上,会用PreparedStatement的方法来进行参数设置
typeHandler.setParameter(ps, i + 1, value, jdbcType);
} catch (TypeException e) {
throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
} catch (SQLException e) {
throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
}
}
}
}
}
可以看到,使用了TypeHandler的setParameter方法来设置参数,ParameterHandler的实现相对简单。