ObjectWrapper实现的属性表达式解析功能，是委托给MetaObject实现的。
/**
* @author Clinton Begin
*/
public class MetaObject {
// 原生对象，即MetaObject所表示的对象
private final Object originalObject;
private final ObjectWrapper objectWrapper;
private final ObjectFactory objectFactory;
private final ObjectWrapperFactory objectWrapperFactory;
private final ReflectorFactory reflectorFactory;
private MetaObject(Object object, ObjectFactory objectFactory, ObjectWrapperFactory objectWrapperFactory, ReflectorFactory reflectorFactory) {
this.originalObject = object;
this.objectFactory = objectFactory;
this.objectWrapperFactory = objectWrapperFactory;
this.reflectorFactory = reflectorFactory;
// 根据对象类型，使用不同的wrapper方法
if (object instanceof ObjectWrapper) {
this.objectWrapper = (ObjectWrapper) object;
} else if (objectWrapperFactory.hasWrapperFor(object)) {
this.objectWrapper = objectWrapperFactory.getWrapperFor(this, object);
} else if (object instanceof Map) {
this.objectWrapper = new MapWrapper(this, (Map) object);
} else if (object instanceof Collection) {
this.objectWrapper = new CollectionWrapper(this, (Collection) object);
} else {
this.objectWrapper = new BeanWrapper(this, object);
}
}
public static MetaObject forObject(Object object, ObjectFactory objectFactory, ObjectWrapperFactory objectWrapperFactory, ReflectorFactory reflectorFactory) {
if (object == null) {
return SystemMetaObject.NULL_META_OBJECT;
} else {
return new MetaObject(object, objectFactory, objectWrapperFactory, reflectorFactory);
}
}
// 从MetaObject中，获取某个字段的属性值
public Object getValue(String name) {
PropertyTokenizer prop = new PropertyTokenizer(name);
if (prop.hasNext()) {
MetaObject metaValue = metaObjectForProperty(prop.getIndexedName());
if (metaValue == SystemMetaObject.NULL_META_OBJECT) {
return null;
} else {
return metaValue.getValue(prop.getChildren());
}
} else {
return objectWrapper.get(prop);
}
}
// 对MetaObject中某个字段进行赋值
public void setValue(String name, Object value) {
PropertyTokenizer prop = new PropertyTokenizer(name);
if (prop.hasNext()) {
MetaObject metaValue = metaObjectForProperty(prop.getIndexedName());
if (metaValue == SystemMetaObject.NULL_META_OBJECT) {
if (value == null) {
// don't instantiate child path if value is null
return;
} else {
metaValue = objectWrapper.instantiatePropertyValue(name, prop, objectFactory);
}
}
metaValue.setValue(prop.getChildren(), value);
} else {
objectWrapper.set(prop, value);
}
}
// 其他方法
c.类型转换
JDBC 数据类型与Java 语言中的数据类型井不是完全对应的，所以在PreparedStatement 为SQL 语句绑定参数时，需要从Java 类型转换成JDBC 类型，而从结果集中获取数据时，则需要从JDBC 类型转换成Java 类型。My Batis 使用类型模块完成上述两种转换。
TypeHandler
/**
* @author Clinton Begin
*/
public interface TypeHandler<T> {
// 设置参数。在通过PreparedStatement 为SQL 语句绑定参数时，会将数据由Java 类型转换成JdbcType 类型
// 《Mybatis技术内幕》这部分的解释反了，详见入参与功能实现代码
void setParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException;
// 获取结果。
// 从ResultSet 中获取数据时会调用此方法，会将数据由Java 类型转换成JdbcType 类型
T getResult(ResultSet rs, String columnName) throws SQLException;
T getResult(ResultSet rs, int columnIndex) throws SQLException;
T getResult(CallableStatement cs, int columnIndex) throws SQLException;
}
BaseTypeHandler
public abstract class BaseTypeHandler<T> extends TypeReference<T> implements TypeHandler<T> {
@Deprecated
protected Configuration configuration;
@Deprecated
public void setConfiguration(Configuration c) {
this.configuration = c;
}
@Override
public void setParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException {
if (parameter == null) {
if (jdbcType == null) {
throw new TypeException("JDBC requires that the JdbcType must be specified for all nullable parameters.");
}
try {
ps.setNull(i, jdbcType.TYPE_CODE);
} catch (SQLException e) {
throw new TypeException("Error setting null for parameter #" + i + " with JdbcType " + jdbcType + " . "
+ "Try setting a different JdbcType for this parameter or a different jdbcTypeForNull configuration property. "
+ "Cause: " + e, e);
}
} else {
try {
// 设置参数，该方法具体有子类实现
setNonNullParameter(ps, i, parameter, jdbcType);
} catch (Exception e) {
throw new TypeException("Error setting non null for parameter #" + i + " with JdbcType " + jdbcType + " . "
+ "Try setting a different JdbcType for this parameter or a different configuration property. "
+ "Cause: " + e, e);
}
}
}
@Override
public T getResult(ResultSet rs, String columnName) throws SQLException {
try {
return getNullableResult(rs, columnName);
} catch (Exception e) {
throw new ResultMapException("Error attempting to get column '" + columnName + "' from result set. Cause: " + e, e);
}
}
@Override
public T getResult(ResultSet rs, int columnIndex) throws SQLException {
try {
return getNullableResult(rs, columnIndex);
} catch (Exception e) {
throw new ResultMapException("Error attempting to get column #" + columnIndex + " from result set. Cause: " + e, e);
}
}
@Override
public T getResult(CallableStatement cs, int columnIndex) throws SQLException {
try {
return getNullableResult(cs, columnIndex);
} catch (Exception e) {
throw new ResultMapException("Error attempting to get column #" + columnIndex + " from callable statement. Cause: " + e, e);
}
}
public abstract void setNonNullParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException;
public abstract T getNullableResult(ResultSet rs, String columnName) throws SQLException;
public abstract T getNullableResult(ResultSet rs, int columnIndex) throws SQLException;
public abstract T getNullableResult(CallableStatement cs, int columnIndex) throws SQLException;
}
实现子类的类型转换，最终还是会落到JDBC的PreparedStatement/ResultSet中对应的类型转换方法。
而PreparedStatement/ResultSet，是由入参带入的。
TypeHandlerRegistry&TypeAliasRegistry，主要是进行类型处理器&类型别名的管理（类似IOC容器对Bean的管理）。
d.数据源模块
