深入浅出Mybatis系列（五）---TypeHandler简介及配置（mybatis源码篇）
上篇文章《深入浅出 Mybatis 系列（四）--- 配置详解之 typeAliases 别名（mybatis 源码篇）》为大家介绍了 mybatis 中别名的使用，以及其源码。本篇将为大家介绍 TypeHandler， 并简单分析其源码。
Mybatis 中的 TypeHandler 是什么？
无论是 MyBatis 在预处理语句（PreparedStatement）中设置一个参数时，还是从结果集中取出一个值时，都会用类型处理器将获取的值以合适的方式转换成 Java 类型。Mybatis 默认为我们实现了许多 TypeHandler, 当我们没有配置指定 TypeHandler 时，Mybatis 会根据参数或者返回结果的不同，默认为我们选择合适的 TypeHandler 处理。
那么，Mybatis 为我们实现了哪些 TypeHandler 呢? 我们怎么自定义实现一个 TypeHandler ? 这些都会在接下来的 mybatis 的源码中看到。
在看源码之前，还是像之前一样，先看看怎么配置吧？
配置 TypeHandler:
<configuration> <typeHandlers> <!-- 当配置 package 的时候，mybatis 会去配置的 package 扫描 TypeHandler <package name="com.dy.demo"/> --><span style="color: rgba(0, 128, 0, 1)"><!--</span><span style="color: rgba(0, 128, 0, 1)"> handler属性直接配置我们要指定的TypeHandler </span><span style="color: rgba(0, 128, 0, 1)">--></span> <span style="color: rgba(0, 0, 255, 1)"><</span><span style="color: rgba(128, 0, 0, 1)">typeHandler </span><span style="color: rgba(255, 0, 0, 1)">handler</span><span style="color: rgba(0, 0, 255, 1)">=""</span><span style="color: rgba(0, 0, 255, 1)">/></span> <span style="color: rgba(0, 128, 0, 1)"><!--</span><span style="color: rgba(0, 128, 0, 1)"> javaType 配置java类型，例如String, 如果配上javaType, 那么指定的typeHandler就只作用于指定的类型 </span><span style="color: rgba(0, 128, 0, 1)">--></span> <span style="color: rgba(0, 0, 255, 1)"><</span><span style="color: rgba(128, 0, 0, 1)">typeHandler </span><span style="color: rgba(255, 0, 0, 1)">javaType</span><span style="color: rgba(0, 0, 255, 1)">=""</span><span style="color: rgba(255, 0, 0, 1)"> handler</span><span style="color: rgba(0, 0, 255, 1)">=""</span><span style="color: rgba(0, 0, 255, 1)">/></span> <span style="color: rgba(0, 128, 0, 1)"><!--</span><span style="color: rgba(0, 128, 0, 1)"> jdbcType 配置数据库基本数据类型，例如varchar, 如果配上jdbcType, 那么指定的typeHandler就只作用于指定的类型 </span><span style="color: rgba(0, 128, 0, 1)">--></span> <span style="color: rgba(0, 0, 255, 1)"><</span><span style="color: rgba(128, 0, 0, 1)">typeHandler </span><span style="color: rgba(255, 0, 0, 1)">jdbcType</span><span style="color: rgba(0, 0, 255, 1)">=""</span><span style="color: rgba(255, 0, 0, 1)"> handler</span><span style="color: rgba(0, 0, 255, 1)">=""</span><span style="color: rgba(0, 0, 255, 1)">/></span> <span style="color: rgba(0, 128, 0, 1)"><!--</span><span style="color: rgba(0, 128, 0, 1)"> 也可两者都配置 </span><span style="color: rgba(0, 128, 0, 1)">--></span> <span style="color: rgba(0, 0, 255, 1)"><</span><span style="color: rgba(128, 0, 0, 1)">typeHandler </span><span style="color: rgba(255, 0, 0, 1)">javaType</span><span style="color: rgba(0, 0, 255, 1)">=""</span><span style="color: rgba(255, 0, 0, 1)"> jdbcType</span><span style="color: rgba(0, 0, 255, 1)">=""</span><span style="color: rgba(255, 0, 0, 1)"> handler</span><span style="color: rgba(0, 0, 255, 1)">=""</span><span style="color: rgba(0, 0, 255, 1)">/></span></typeHandlers>
......
</configuration>
上面简单介绍了一下 TypeHandler, 下面就看看 mybatis 中 TypeHandler 的源码了。
========================================================= 我是源码分割线 ==========================================================
老规矩，先从对 xml 的解析讲起：
/** * 解析 typeHandlers 节点 */ private void typeHandlerElement(XNode parent) throws Exception { if (parent != null) { for (XNode child : parent.getChildren()) { //子节点为 package 时，获取其 name 属性的值，然后自动扫描 package 下的自定义 typeHandler if ("package".equals(child.getName())) { String typeHandlerPackage = child.getStringAttribute("name"); typeHandlerRegistry.register(typeHandlerPackage); } else { //子节点为 typeHandler 时， 可以指定 javaType 属性， 也可以指定 jdbcType, 也可两者都指定 //javaType 是指定 java 类型 //jdbcType 是指定 jdbc 类型（数据库类型： 如 varchar） String javaTypeName = child.getStringAttribute("javaType"); String jdbcTypeName = child.getStringAttribute("jdbcType"); //handler 就是我们配置的 typeHandler String handlerTypeName = child.getStringAttribute("handler"); //resolveClass 方法就是我们上篇文章所讲的 TypeAliasRegistry 里面处理别名的方法 Class<?> javaTypeClass = resolveClass(javaTypeName); //JdbcType 是一个枚举类型，resolveJdbcType 方法是在获取枚举类型的值 JdbcType jdbcType = resolveJdbcType(jdbcTypeName); Class<?> typeHandlerClass = resolveClass(handlerTypeName); //注册 typeHandler, typeHandler 通过 TypeHandlerRegistry 这个类管理 if (javaTypeClass != null) { if (jdbcType == null) {typeHandlerRegistry.register(javaTypeClass, typeHandlerClass); } else {typeHandlerRegistry.register(javaTypeClass, jdbcType, typeHandlerClass); } } else {typeHandlerRegistry.register(typeHandlerClass); } } } } }
接下来看看 TypeHandler 的管理注册类：
TypeHandlerRegistry：
/** * typeHandler 注册管理类 */ public final class TypeHandlerRegistry {//源码一上来，二话不说，几个大大的 HashMap 就出现，这不又跟上次讲的 typeAliases 的注册类似么
//基本数据类型与其包装类
private static final Map<Class<?>, Class<?>> reversePrimitiveMap = new HashMap<Class<?>, Class<?>>() {
private static final long serialVersionUID = 1L;
{
put(Byte.class, byte.class);
put(Short.class, short.class);
put(Integer.class, int.class);
put(Long.class, long.class);
put(Float.class, float.class);
put(Double.class, double.class);
put(Boolean.class, boolean.class);
put(Character.class, char.class);
}
};//这几个 MAP 不用说就知道存的是什么东西吧，命名的好处
private final Map<JdbcType, TypeHandler<?>> JDBC_TYPE_HANDLER_MAP = new EnumMap<JdbcType, TypeHandler<?>>(JdbcType.class);
private final Map<Type, Map<JdbcType, TypeHandler<?>>> TYPE_HANDLER_MAP = new HashMap<Type, Map<JdbcType, TypeHandler<?>>>();
private final TypeHandler<Object> UNKNOWN_TYPE_HANDLER = new UnknownTypeHandler(this);
private final Map<Class<?>, TypeHandler<?>> ALL_TYPE_HANDLERS_MAP = new HashMap<Class<?>, TypeHandler<?>>();//就像上篇文章讲的 typeAliases 一样，mybatis 也默认给我们注册了不少的 typeHandler
//具体如下
public TypeHandlerRegistry() {
register(Boolean.class, new BooleanTypeHandler());
register(boolean.class, new BooleanTypeHandler());
register(JdbcType.BOOLEAN, new BooleanTypeHandler());
register(JdbcType.BIT, new BooleanTypeHandler());register(Byte.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> ByteTypeHandler()); register(</span><span style="color: rgba(0, 0, 255, 1)">byte</span>.<span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> ByteTypeHandler()); register(JdbcType.TINYINT, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> ByteTypeHandler()); register(Short.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> ShortTypeHandler()); register(</span><span style="color: rgba(0, 0, 255, 1)">short</span>.<span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> ShortTypeHandler()); register(JdbcType.SMALLINT, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> ShortTypeHandler()); register(Integer.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> IntegerTypeHandler()); register(</span><span style="color: rgba(0, 0, 255, 1)">int</span>.<span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> IntegerTypeHandler()); register(JdbcType.INTEGER, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> IntegerTypeHandler()); register(Long.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> LongTypeHandler()); register(</span><span style="color: rgba(0, 0, 255, 1)">long</span>.<span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> LongTypeHandler()); register(Float.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> FloatTypeHandler()); register(</span><span style="color: rgba(0, 0, 255, 1)">float</span>.<span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> FloatTypeHandler()); register(JdbcType.FLOAT, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> FloatTypeHandler()); register(Double.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> DoubleTypeHandler()); register(</span><span style="color: rgba(0, 0, 255, 1)">double</span>.<span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> DoubleTypeHandler()); register(JdbcType.DOUBLE, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> DoubleTypeHandler()); register(String.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> StringTypeHandler()); register(String.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, JdbcType.CHAR, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> StringTypeHandler()); register(String.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, JdbcType.CLOB, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> ClobTypeHandler()); register(String.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, JdbcType.VARCHAR, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> StringTypeHandler()); register(String.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, JdbcType.LONGVARCHAR, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> ClobTypeHandler()); register(String.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, JdbcType.NVARCHAR, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> NStringTypeHandler()); register(String.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, JdbcType.NCHAR, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> NStringTypeHandler()); register(String.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, JdbcType.NCLOB, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> NClobTypeHandler()); register(JdbcType.CHAR, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> StringTypeHandler()); register(JdbcType.VARCHAR, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> StringTypeHandler()); register(JdbcType.CLOB, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> ClobTypeHandler()); register(JdbcType.LONGVARCHAR, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> ClobTypeHandler()); register(JdbcType.NVARCHAR, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> NStringTypeHandler()); register(JdbcType.NCHAR, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> NStringTypeHandler()); register(JdbcType.NCLOB, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> NClobTypeHandler()); register(Object.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, JdbcType.ARRAY, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> ArrayTypeHandler()); register(JdbcType.ARRAY, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> ArrayTypeHandler()); register(BigInteger.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> BigIntegerTypeHandler()); register(JdbcType.BIGINT, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> LongTypeHandler()); register(BigDecimal.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> BigDecimalTypeHandler()); register(JdbcType.REAL, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> BigDecimalTypeHandler()); register(JdbcType.DECIMAL, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> BigDecimalTypeHandler()); register(JdbcType.NUMERIC, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> BigDecimalTypeHandler()); register(Byte[].</span><span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> ByteObjectArrayTypeHandler()); register(Byte[].</span><span style="color: rgba(0, 0, 255, 1)">class</span>, JdbcType.BLOB, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> BlobByteObjectArrayTypeHandler()); register(Byte[].</span><span style="color: rgba(0, 0, 255, 1)">class</span>, JdbcType.LONGVARBINARY, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> BlobByteObjectArrayTypeHandler()); register(</span><span style="color: rgba(0, 0, 255, 1)">byte</span>[].<span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> ByteArrayTypeHandler()); register(</span><span style="color: rgba(0, 0, 255, 1)">byte</span>[].<span style="color: rgba(0, 0, 255, 1)">class</span>, JdbcType.BLOB, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> BlobTypeHandler()); register(</span><span style="color: rgba(0, 0, 255, 1)">byte</span>[].<span style="color: rgba(0, 0, 255, 1)">class</span>, JdbcType.LONGVARBINARY, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> BlobTypeHandler()); register(JdbcType.LONGVARBINARY, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> BlobTypeHandler()); register(JdbcType.BLOB, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> BlobTypeHandler()); register(Object.</span><span style="color: rgba(0, 0, 255, 1)">class</span><span style="color: rgba(0, 0, 0, 1)">, UNKNOWN_TYPE_HANDLER); register(Object.</span><span style="color: rgba(0, 0, 255, 1)">class</span><span style="color: rgba(0, 0, 0, 1)">, JdbcType.OTHER, UNKNOWN_TYPE_HANDLER); register(JdbcType.OTHER, UNKNOWN_TYPE_HANDLER); register(Date.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> DateTypeHandler()); register(Date.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, JdbcType.DATE, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> DateOnlyTypeHandler()); register(Date.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, JdbcType.TIME, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> TimeOnlyTypeHandler()); register(JdbcType.TIMESTAMP, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> DateTypeHandler()); register(JdbcType.DATE, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> DateOnlyTypeHandler()); register(JdbcType.TIME, </span><span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> TimeOnlyTypeHandler()); register(java.sql.Date.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> SqlDateTypeHandler()); register(java.sql.Time.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> SqlTimeTypeHandler()); register(java.sql.Timestamp.</span><span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> SqlTimestampTypeHandler()); </span><span style="color: rgba(0, 128, 0, 1)">//</span><span style="color: rgba(0, 128, 0, 1)"> issue #273</span> register(Character.<span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> CharacterTypeHandler()); register(</span><span style="color: rgba(0, 0, 255, 1)">char</span>.<span style="color: rgba(0, 0, 255, 1)">class</span>, <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> CharacterTypeHandler());}
public boolean hasTypeHandler(Class<?> javaType) {
return hasTypeHandler(javaType, null);
}public boolean hasTypeHandler(TypeReference<?> javaTypeReference) {
return hasTypeHandler(javaTypeReference, null);
}public boolean hasTypeHandler(Class<?> javaType, JdbcType jdbcType) {
return javaType != null && getTypeHandler((Type) javaType, jdbcType) != null;
}public boolean hasTypeHandler(TypeReference<?> javaTypeReference, JdbcType jdbcType) {
return javaTypeReference != null && getTypeHandler(javaTypeReference, jdbcType) != null;
}public TypeHandler<?> getMappingTypeHandler(Class<? extends TypeHandler<?>> handlerType) {
return ALL_TYPE_HANDLERS_MAP.get(handlerType);
}public <T> TypeHandler<T> getTypeHandler(Class<T> type) {
return getTypeHandler((Type) type, null);
}public <T> TypeHandler<T> getTypeHandler(TypeReference<T> javaTypeReference) {
return getTypeHandler(javaTypeReference, null);
}public TypeHandler<?> getTypeHandler(JdbcType jdbcType) {
return JDBC_TYPE_HANDLER_MAP.get(jdbcType);
}public <T> TypeHandler<T> getTypeHandler(Class<T> type, JdbcType jdbcType) {
return getTypeHandler((Type) type, jdbcType);
}public <T> TypeHandler<T> getTypeHandler(TypeReference<T> javaTypeReference, JdbcType jdbcType) {
return getTypeHandler(javaTypeReference.getRawType(), jdbcType);
}private <T> TypeHandler<T> getTypeHandler(Type type, JdbcType jdbcType) {
Map<JdbcType, TypeHandler<?>> jdbcHandlerMap = TYPE_HANDLER_MAP.get(type);
TypeHandler<?> handler = null;
if (jdbcHandlerMap != null) {
handler = jdbcHandlerMap.get(jdbcType);
if (handler == null) {
handler = jdbcHandlerMap.get(null);
}
}
if (handler == null && type != null && type instanceof Class && Enum.class.isAssignableFrom((Class<?>)type)) {
handler = new EnumTypeHandler((Class<?>)type);
}
@SuppressWarnings("unchecked")
// type drives generics here
TypeHandler<T> returned = (TypeHandler<T>) handler;
return returned;
}public TypeHandler<Object> getUnknownTypeHandler() {
return UNKNOWN_TYPE_HANDLER;
}public void register(JdbcType jdbcType, TypeHandler<?> handler) {
JDBC_TYPE_HANDLER_MAP.put(jdbcType, handler);
}//
// REGISTER INSTANCE
//
/**
- 只配置了 typeHandler, 没有配置 jdbcType 或者 javaType
*/
@SuppressWarnings("unchecked")
public <T> void register(TypeHandler<T> typeHandler) {
boolean mappedTypeFound = false;
//在自定义 typeHandler 的时候，可以加上注解 MappedTypes 去指定关联的 javaType
//因此，此处需要扫描 MappedTypes 注解
MappedTypes mappedTypes = typeHandler.getClass().getAnnotation(MappedTypes.class);
if (mappedTypes != null) {
for (Class<?> handledType : mappedTypes.value()) {
register(handledType, typeHandler);
mappedTypeFound = true;
}
}
// @since 3.1.0 - try to auto-discover the mapped type
if (!mappedTypeFound && typeHandler instanceof TypeReference) {
try {
TypeReference<T> typeReference = (TypeReference<T>) typeHandler;
register(typeReference.getRawType(), typeHandler);
mappedTypeFound = true;
} catch (Throwable t) {
// maybe users define the TypeReference with a different type and are not assignable, so just ignore it
}
}
if (!mappedTypeFound) {
register((Class<T>) null, typeHandler);
}
}/**
- 配置了 typeHandlerhe 和 javaType
*/
public <T> void register(Class<T> javaType, TypeHandler<? extends T> typeHandler) {
register((Type) javaType, typeHandler);
}private <T> void register(Type javaType, TypeHandler<? extends T> typeHandler) {
//扫描注解 MappedJdbcTypes
MappedJdbcTypes mappedJdbcTypes = typeHandler.getClass().getAnnotation(MappedJdbcTypes.class);
if (mappedJdbcTypes != null) {
for (JdbcType handledJdbcType : mappedJdbcTypes.value()) {
register(javaType, handledJdbcType, typeHandler);
}
if (mappedJdbcTypes.includeNullJdbcType()) {
register(javaType, null, typeHandler);
}
} else {
register(javaType, null, typeHandler);
}
}public <T> void register(TypeReference<T> javaTypeReference, TypeHandler<? extends T> handler) {
register(javaTypeReference.getRawType(), handler);
}/**
- typeHandlerhe、javaType、jdbcType 都配置了
*/
public <T> void register(Class<T> type, JdbcType jdbcType, TypeHandler<? extends T> handler) {
register((Type) type, jdbcType, handler);
}/**
- 注册 typeHandler 的核心方法
- 就是向 Map 新增数据而已
*/
private void register(Type javaType, JdbcType jdbcType, TypeHandler<?> handler) {
if (javaType != null) {
Map<JdbcType, TypeHandler<?>> map = TYPE_HANDLER_MAP.get(javaType);
if (map == null) {
map = new HashMap<JdbcType, TypeHandler<?>>();
TYPE_HANDLER_MAP.put(javaType, map);
}
map.put(jdbcType, handler);
if (reversePrimitiveMap.containsKey(javaType)) {
register(reversePrimitiveMap.get(javaType), jdbcType, handler);
}
}
ALL_TYPE_HANDLERS_MAP.put(handler.getClass(), handler);
}//
// REGISTER CLASS
//// Only handler type
public void register(Class<?> typeHandlerClass) {
boolean mappedTypeFound = false;
MappedTypes mappedTypes = typeHandlerClass.getAnnotation(MappedTypes.class);
if (mappedTypes != null) {
for (Class<?> javaTypeClass : mappedTypes.value()) {
register(javaTypeClass, typeHandlerClass);
mappedTypeFound = true;
}
}
if (!mappedTypeFound) {
register(getInstance(null, typeHandlerClass));
}
}// java type + handler type
public void register(Class<?> javaTypeClass, Class<?> typeHandlerClass) {
register(javaTypeClass, getInstance(javaTypeClass, typeHandlerClass));
}// java type + jdbc type + handler type
public void register(Class<?> javaTypeClass, JdbcType jdbcType, Class<?> typeHandlerClass) {
register(javaTypeClass, jdbcType, getInstance(javaTypeClass, typeHandlerClass));
}// Construct a handler (used also from Builders)
@SuppressWarnings("unchecked")
public <T> TypeHandler<T> getInstance(Class<?> javaTypeClass, Class<?> typeHandlerClass) {
if (javaTypeClass != null) {
try {
Constructor<?> c = typeHandlerClass.getConstructor(Class.class);
return (TypeHandler<T>)c.newInstance(javaTypeClass);
} catch (NoSuchMethodException ignored) {
// ignored
} catch (Exception e) {
throw new TypeException("Failed invoking constructor for handler" + typeHandlerClass, e);
}
}
try {
Constructor<?> c = typeHandlerClass.getConstructor();
return (TypeHandler<T>)c.newInstance();
} catch (Exception e) {
throw new TypeException("Unable to find a usable constructor for" + typeHandlerClass, e);
}
}/**
- 根据指定的 pacakge 去扫描自定义的 typeHander，然后注册
*/
public void register(String packageName) {
ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<Class<?>>();
resolverUtil.find(new ResolverUtil.IsA(TypeHandler.class), packageName);
Set<Class<? extends Class<?>>> handlerSet = resolverUtil.getClasses();
for (Class<?> type : handlerSet) {
//Ignore inner classes and interfaces (including package-info.java) and abstract classes
if (!type.isAnonymousClass() && !type.isInterface() && !Modifier.isAbstract(type.getModifiers())) {
register(type);
}
}
}// get information
/**
- 通过 configuration 对象可以获取已注册的所有 typeHandler
*/
public Collection<TypeHandler<?>> getTypeHandlers() {
return Collections.unmodifiableCollection(ALL_TYPE_HANDLERS_MAP.values());
}}
由源码可以看到， mybatis 为我们实现了那么多 TypeHandler, 随便打开一个 TypeHandler，看其源码，都可以看到，它继承自一个抽象类：BaseTypeHandler， 那么我们是不是也能通过继承 BaseTypeHandler，从而实现自定义的 TypeHandler ? 答案是肯定的， 那么现在下面就为大家演示一下自定义 TypeHandler:
===================================================== 自定义 TypeHandler 分割线 ============================================================
ExampleTypeHandler:
@MappedJdbcTypes(JdbcType.VARCHAR)
// 此处如果不用注解指定 jdbcType, 那么，就可以在配置文件中通过 "jdbcType" 属性指定， 同理， javaType 也可通过 @MappedTypes 指定 public class ExampleTypeHandler extends BaseTypeHandler<String> {@Override
public void setNonNullParameter(PreparedStatement ps, int i, String parameter, JdbcType jdbcType) throws SQLException {
ps.setString(i, parameter);
}@Override
public String getNullableResult(ResultSet rs, String columnName) throws SQLException {
return rs.getString(columnName);
}@Override
public String getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
return rs.getString(columnIndex);
}@Override
public String getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
return cs.getString(columnIndex);
}
}
然后，就该配置我们的自定义 TypeHandler 了：
<configuration> <typeHandlers> <!-- 由于自定义的 TypeHandler 在定义时已经通过注解指定了 jdbcType, 所以此处不用再配置 jdbcType --> <typeHandler handler="ExampleTypeHandler"/> </typeHandlers>......
</configuration>
也就是说，我们在自定义 TypeHandler 的时候，可以在 TypeHandler 通过 @MappedJdbcTypes 指定 jdbcType, 通过 @MappedTypes 指定 javaType, 如果没有使用注解指定，那么我们就需要在配置文件中配置。
好啦，本篇文章到此结束。