Mybatis 系列5
阿新 • • 發佈：2018-05-06
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上篇系列4中 為大家介紹了mybatis中別名的使用，以及其源碼。本篇將為大家介紹TypeHandler， 並簡單分析其源碼。
Mybatis中的TypeHandler是什麽？
無論是 MyBatis 在預處理語句（PreparedStatement）中設置一個參數時，還是從結果集中取出一個值時，都會用類型處理器將獲取的值以合適的方式轉換成 Java 類型。Mybatis默認為我們實現了許多TypeHandler, 當我們沒有配置指定TypeHandler時，Mybatis會根據參數或者返回結果的不同，默認為我們選擇合適的TypeHandler處理。
那麽，Mybatis為我們實現了哪些TypeHandler呢? 我們怎麽自定義實現一個TypeHandler ?
這些都會在接下來的mybatis的源碼中看到。
在看源碼之前，還是像之前一樣，先看看怎麽配置吧？
配置TypeHandler:
1 <configuration> 2 <typeHandlers> 3 <!-- 4 當配置package的時候，mybatis會去配置的package掃描TypeHandler 5 <package name="com.dy.demo"/> 6 --> 7 8 <!-- handler屬性直接配置我們要指定的TypeHandler --> 9<typeHandler handler=""/> 10 11 <!-- javaType 配置java類型，例如String, 如果配上javaType, 那麽指定的typeHandler就只作用於指定的類型 --> 12 <typeHandler javaType="" handler=""/> 13 14 <!-- jdbcType 配置數據庫基本數據類型，例如varchar, 如果配上jdbcType, 那麽指定的typeHandler就只作用於指定的類型 --> 15<typeHandler jdbcType="" handler=""/> 16 17 <!-- 也可兩者都配置 --> 18 <typeHandler javaType="" jdbcType="" handler=""/> 19 20 </typeHandlers> 21 22 ...... 23 24 </configuration>
上面簡單介紹了一下TypeHandler, 下面就看看mybatis中TypeHandler的源碼了。
=我是源碼分割線== 老規矩，先從對xml的解析講起：
1 /** 2 * 解析typeHandlers節點 3 */ 4 private void typeHandlerElement(XNode parent) throws Exception { 5 if (parent != null) { 6 for (XNode child : parent.getChildren()) { 7 //子節點為package時，獲取其name屬性的值，然後自動掃描package下的自定義typeHandler 8 if ("package".equals(child.getName())) { 9 String typeHandlerPackage = child.getStringAttribute("name"); 10 typeHandlerRegistry.register(typeHandlerPackage); 11 } else { 12 //子節點為typeHandler時， 可以指定javaType屬性， 也可以指定jdbcType, 也可兩者都指定 13 //javaType 是指定java類型 14 //jdbcType 是指定jdbc類型（數據庫類型： 如varchar） 15 String javaTypeName = child.getStringAttribute("javaType"); 16 String jdbcTypeName = child.getStringAttribute("jdbcType"); 17 //handler就是我們配置的typeHandler 18 String handlerTypeName = child.getStringAttribute("handler"); 19 //resolveClass方法就是我們上篇文章所講的TypeAliasRegistry裏面處理別名的方法 20 Class<?> javaTypeClass = resolveClass(javaTypeName); 21 //JdbcType是一個枚舉類型，resolveJdbcType方法是在獲取枚舉類型的值 22 JdbcType jdbcType = resolveJdbcType(jdbcTypeName); 23 Class<?> typeHandlerClass = resolveClass(handlerTypeName); 24 //註冊typeHandler, typeHandler通過TypeHandlerRegistry這個類管理 25 if (javaTypeClass != null) { 26 if (jdbcType == null) { 27 typeHandlerRegistry.register(javaTypeClass, typeHandlerClass); 28 } else { 29 typeHandlerRegistry.register(javaTypeClass, jdbcType, typeHandlerClass); 30 } 31 } else { 32 typeHandlerRegistry.register(typeHandlerClass); 33 } 34 } 35 } 36 } 37 }
接下來看看TypeHandler的管理註冊類：
TypeHandlerRegistry：
1 /** 2 * typeHandler註冊管理類 3 */ 4 public final class TypeHandlerRegistry { 5 6 //源碼一上來，二話不說，幾個大大的HashMap就出現，這不又跟上次講的typeAliases的註冊類似麽 7 8 //基本數據類型與其包裝類 9 private static final Map<Class<?>, Class<?>> reversePrimitiveMap = new HashMap<Class<?>, Class<?>>() { 10 private static final long serialVersionUID = 1L; 11 { 12 put(Byte.class, byte.class); 13 put(Short.class, short.class); 14 put(Integer.class, int.class); 15 put(Long.class, long.class); 16 put(Float.class, float.class); 17 put(Double.class, double.class); 18 put(Boolean.class, boolean.class); 19 put(Character.class, char.class); 20 } 21 }; 22 23 //這幾個MAP不用說就知道存的是什麽東西吧，命名的好處 24 private final Map<JdbcType, TypeHandler<?>> JDBC_TYPE_HANDLER_MAP = new EnumMap<JdbcType, TypeHandler<?>>(JdbcType.class); 25 private final Map<Type, Map<JdbcType, TypeHandler<?>>> TYPE_HANDLER_MAP = new HashMap<Type, Map<JdbcType, TypeHandler<?>>>(); 26 private final TypeHandler<Object> UNKNOWN_TYPE_HANDLER = new UnknownTypeHandler(this); 27 private final Map<Class<?>, TypeHandler<?>> ALL_TYPE_HANDLERS_MAP = new HashMap<Class<?>, TypeHandler<?>>(); 28 29 //就像上篇文章講的typeAliases一樣，mybatis也默認給我們註冊了不少的typeHandler 30 //具體如下 31 public TypeHandlerRegistry() { 32 register(Boolean.class, new BooleanTypeHandler()); 33 register(boolean.class, new BooleanTypeHandler()); 34 register(JdbcType.BOOLEAN, new BooleanTypeHandler()); 35 register(JdbcType.BIT, new BooleanTypeHandler()); 36 37 register(Byte.class, new ByteTypeHandler()); 38 register(byte.class, new ByteTypeHandler()); 39 register(JdbcType.TINYINT, new ByteTypeHandler()); 40 41 register(Short.class, new ShortTypeHandler()); 42 register(short.class, new ShortTypeHandler()); 43 register(JdbcType.SMALLINT, new ShortTypeHandler()); 44 45 register(Integer.class, new IntegerTypeHandler()); 46 register(int.class, new IntegerTypeHandler()); 47 register(JdbcType.INTEGER, new IntegerTypeHandler()); 48 49 register(Long.class, new LongTypeHandler()); 50 register(long.class, new LongTypeHandler()); 51 52 register(Float.class, new FloatTypeHandler()); 53 register(float.class, new FloatTypeHandler()); 54 register(JdbcType.FLOAT, new FloatTypeHandler()); 55 56 register(Double.class, new DoubleTypeHandler()); 57 register(double.class, new DoubleTypeHandler()); 58 register(JdbcType.DOUBLE, new DoubleTypeHandler()); 59 60 register(String.class, new StringTypeHandler()); 61 register(String.class, JdbcType.CHAR, new StringTypeHandler()); 62 register(String.class, JdbcType.CLOB, new ClobTypeHandler()); 63 register(String.class, JdbcType.VARCHAR, new StringTypeHandler()); 64 register(String.class, JdbcType.LONGVARCHAR, new ClobTypeHandler()); 65 register(String.class, JdbcType.NVARCHAR, new NStringTypeHandler()); 66 register(String.class, JdbcType.NCHAR, new NStringTypeHandler()); 67 register(String.class, JdbcType.NCLOB, new NClobTypeHandler()); 68 register(JdbcType.CHAR, new StringTypeHandler()); 69 register(JdbcType.VARCHAR, new StringTypeHandler()); 70 register(JdbcType.CLOB, new ClobTypeHandler()); 71 register(JdbcType.LONGVARCHAR, new ClobTypeHandler()); 72 register(JdbcType.NVARCHAR, new NStringTypeHandler()); 73 register(JdbcType.NCHAR, new NStringTypeHandler()); 74 register(JdbcType.NCLOB, new NClobTypeHandler()); 75 76 register(Object.class, JdbcType.ARRAY, new ArrayTypeHandler()); 77 register(JdbcType.ARRAY, new ArrayTypeHandler()); 78 79 register(BigInteger.class, new BigIntegerTypeHandler()); 80 register(JdbcType.BIGINT, new LongTypeHandler()); 81 82 register(BigDecimal.class, new BigDecimalTypeHandler()); 83 register(JdbcType.REAL, new BigDecimalTypeHandler()); 84 register(JdbcType.DECIMAL, new BigDecimalTypeHandler()); 85 register(JdbcType.NUMERIC, new BigDecimalTypeHandler()); 86 87 register(Byte[].class, new ByteObjectArrayTypeHandler()); 88 register(Byte[].class, JdbcType.BLOB, new BlobByteObjectArrayTypeHandler()); 89 register(Byte[].class, JdbcType.LONGVARBINARY, new BlobByteObjectArrayTypeHandler()); 90 register(byte[].class, new ByteArrayTypeHandler()); 91 register(byte[].class, JdbcType.BLOB, new BlobTypeHandler()); 92 register(byte[].class, JdbcType.LONGVARBINARY, new BlobTypeHandler()); 93 register(JdbcType.LONGVARBINARY, new BlobTypeHandler()); 94 register(JdbcType.BLOB, new BlobTypeHandler()); 95 96 register(Object.class, UNKNOWN_TYPE_HANDLER); 97 register(Object.class, JdbcType.OTHER, UNKNOWN_TYPE_HANDLER); 98 register(JdbcType.OTHER, UNKNOWN_TYPE_HANDLER); 99 100 register(Date.class, new DateTypeHandler()); 101 register(Date.class, JdbcType.DATE, new DateOnlyTypeHandler()); 102 register(Date.class, JdbcType.TIME, new TimeOnlyTypeHandler()); 103 register(JdbcType.TIMESTAMP, new DateTypeHandler()); 104 register(JdbcType.DATE, new DateOnlyTypeHandler()); 105 register(JdbcType.TIME, new TimeOnlyTypeHandler()); 106 107 register(java.sql.Date.class, new SqlDateTypeHandler()); 108 register(java.sql.Time.class, new SqlTimeTypeHandler()); 109 register(java.sql.Timestamp.class, new SqlTimestampTypeHandler()); 110 111 // issue #273 112 register(Character.class, new CharacterTypeHandler()); 113 register(char.class, new CharacterTypeHandler()); 114 } 115 116 public boolean hasTypeHandler(Class<?> javaType) { 117 return hasTypeHandler(javaType, null); 118 } 119 120 public boolean hasTypeHandler(TypeReference<?> javaTypeReference) { 121 return hasTypeHandler(javaTypeReference, null); 122 } 123 124 public boolean hasTypeHandler(Class<?> javaType, JdbcType jdbcType) { 125 return javaType != null && getTypeHandler((Type) javaType, jdbcType) != null; 126 } 127 128 public boolean hasTypeHandler(TypeReference<?> javaTypeReference, JdbcType jdbcType) { 129 return javaTypeReference != null && getTypeHandler(javaTypeReference, jdbcType) != null; 130 } 131 132 public TypeHandler<?> getMappingTypeHandler(Class<? extends TypeHandler<?>> handlerType) { 133 return ALL_TYPE_HANDLERS_MAP.get(handlerType); 134 } 135 136 public <T> TypeHandler<T> getTypeHandler(Class<T> type) { 137 return getTypeHandler((Type) type, null); 138 } 139 140 public <T> TypeHandler<T> getTypeHandler(TypeReference<T> javaTypeReference) { 141 return getTypeHandler(javaTypeReference, null); 142 } 143 144 public TypeHandler<?> getTypeHandler(JdbcType jdbcType) { 145 return JDBC_TYPE_HANDLER_MAP.get(jdbcType); 146 } 147 148 public <T> TypeHandler<T> getTypeHandler(Class<T> type, JdbcType jdbcType) { 149 return getTypeHandler((Type) type, jdbcType); 150 } 151 152 public <T> TypeHandler<T> getTypeHandler(TypeReference<T> javaTypeReference, JdbcType jdbcType) { 153 return getTypeHandler(javaTypeReference.getRawType(), jdbcType); 154 } 155 156 private <T> TypeHandler<T> getTypeHandler(Type type, JdbcType jdbcType) { 157 Map<JdbcType, TypeHandler<?>> jdbcHandlerMap = TYPE_HANDLER_MAP.get(type); 158 TypeHandler<?> handler = null; 159 if (jdbcHandlerMap != null) { 160 handler = jdbcHandlerMap.get(jdbcType); 161 if (handler == null) { 162 handler = jdbcHandlerMap.get(null); 163 } 164 } 165 if (handler == null && type != null && type instanceof Class && Enum.class.isAssignableFrom((Class<?>) type)) { 166 handler = new EnumTypeHandler((Class<?>) type); 167 } 168 @SuppressWarnings("unchecked") 169 // type drives generics here 170 TypeHandler<T> returned = (TypeHandler<T>) handler; 171 return returned; 172 } 173 174 public TypeHandler<Object> getUnknownTypeHandler() { 175 return UNKNOWN_TYPE_HANDLER; 176 } 177 178 public void register(JdbcType jdbcType, TypeHandler<?> handler) { 179 JDBC_TYPE_HANDLER_MAP.put(jdbcType, handler); 180 } 181 182 // 183 // REGISTER INSTANCE 184 // 185 186 /** 187 * 只配置了typeHandler, 沒有配置jdbcType 或者javaType 188 */ 189 @SuppressWarnings("unchecked") 190 public <T> void register(TypeHandler<T> typeHandler) { 191 boolean mappedTypeFound = false; 192 //在自定義typeHandler的時候，可以加上註解MappedTypes 去指定關聯的javaType 193 //因此，此處需要掃描MappedTypes註解 194 MappedTypes mappedTypes = typeHandler.getClass().getAnnotation(MappedTypes.class); 195 if (mappedTypes != null) { 196 for (Class<?> handledType : mappedTypes.value()) { 197 register(handledType, typeHandler); 198 mappedTypeFound = true; 199 } 200 } 201 // @since 3.1.0 - try to auto-discover the mapped type 202 if (!mappedTypeFound && typeHandler instanceof TypeReference) { 203 try { 204 TypeReference<T> typeReference = (TypeReference<T>) typeHandler; 205 register(typeReference.getRawType(), typeHandler); 206 mappedTypeFound = true; 207 } catch (Throwable t) { 208 // maybe users define the TypeReference with a different type and are not assignable, so just ignore it 209 } 210 } 211 if (!mappedTypeFound) { 212 register((Class<T>) null, typeHandler); 213 } 214 } 215 216 /** 217 * 配置了typeHandlerhe和javaType 218 */ 219 public <T> void register(Class<T> javaType, TypeHandler<? extends T> typeHandler) { 220 register((Type) javaType, typeHandler); 221 } 222 223 private <T> void register(Type javaType, TypeHandler<? extends T> typeHandler) { 224 //掃描註解MappedJdbcTypes 225 MappedJdbcTypes mappedJdbcTypes = typeHandler.getClass().getAnnotation(MappedJdbcTypes.class); 226 if (mappedJdbcTypes != null) { 227 for (JdbcType handledJdbcType : mappedJdbcTypes.value()) { 228 register(javaType, handledJdbcType, typeHandler); 229 } 230 if (mappedJdbcTypes.includeNullJdbcType()) { 231 register(javaType, null, typeHandler); 232 } 233 } else { 234 register(javaType, null, typeHandler); 235 } 236 } 237 238 public <T> void register(TypeReference<T> javaTypeReference, TypeHandler<? extends T> handler) { 239 register(javaTypeReference.getRawType(), handler); 240 } 241 242 /** 243 * typeHandlerhe、javaType、jdbcType都配置了 244 */ 245 public <T> void register(Class<T> type, JdbcType jdbcType, TypeHandler<? extends T> handler) { 246 register((Type) type, jdbcType, handler); 247 } 248 249 /** 250 * 註冊typeHandler的核心方法 251 * 就是向Map新增數據而已 252 */ 253 private void register(Type javaType, JdbcType jdbcType, TypeHandler<?> handler) { 254 if (javaType != null) { 255 Map<JdbcType, TypeHandler<?>> map = TYPE_HANDLER_MAP.get(javaType); 256 if (map == null) { 257 map = new HashMap<JdbcType, TypeHandler<?>>(); 258 TYPE_HANDLER_MAP.put(javaType, map); 259 } 260 map.put(jdbcType, handler); 261 if (reversePrimitiveMap.containsKey(javaType)) { 262 register(reversePrimitiveMap.get(javaType), jdbcType, handler); 263 } 264 } 265 ALL_TYPE_HANDLERS_MAP.put(handler.getClass(), handler); 266 } 267 268 // 269 // REGISTER CLASS 270 // 271 272 // Only handler type 273 274 public void register(Class<?> typeHandlerClass) { 275 boolean mappedTypeFound = false; 276 MappedTypes mappedTypes = typeHandlerClass.getAnnotation(MappedTypes.class); 277 if (mappedTypes != null) { 278 for (Class<?> javaTypeClass : mappedTypes.value()) { 279 register(javaTypeClass, typeHandlerClass); 280 mappedTypeFound = true; 281 } 282 } 283 if (!mappedTypeFound) { 284 register(getInstance(null, typeHandlerClass)); 285 } 286 } 287 288 // java type + handler type 289 290 public void register(Class<?> javaTypeClass, Class<?> typeHandlerClass) { 291 register(javaTypeClass, getInstance(javaTypeClass, typeHandlerClass)); 292 } 293 294 // java type + jdbc type + handler type 295 296 public void register(Class<?> javaTypeClass, JdbcType jdbcType, Class<?> typeHandlerClass) { 297 register(javaTypeClass, jdbcType, getInstance(javaTypeClass, typeHandlerClass)); 298 } 299 300 // Construct a handler (used also from Builders) 301 302 @SuppressWarnings("unchecked") 303 public <T> TypeHandler<T> getInstance(Class<?> javaTypeClass, Class<?> typeHandlerClass) { 304 if (javaTypeClass != null) { 305 try { 306 Constructor<?> c = typeHandlerClass.getConstructor(Class.class); 307 return (TypeHandler<T>) c.newInstance(javaTypeClass); 308 } catch (NoSuchMethodException ignored) { 309 // ignored 310 } catch (Exception e) { 311 throw new TypeException("Failed invoking constructor for handler " + typeHandlerClass, e); 312 } 313 } 314 try { 315 Constructor<?> c = typeHandlerClass.getConstructor(); 316 return (TypeHandler<T>) c.newInstance(); 317 } catch (Exception e) { 318 throw new TypeException("Unable to find a usable constructor for " + typeHandlerClass, e); 319 } 320 } 321 322 323 /** 324 * 根據指定的pacakge去掃描自定義的typeHander，然後註冊 325 */ 326 public void register(String packageName) { 327 ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<Class<?>>(); 328 resolverUtil.find(new ResolverUtil.IsA(TypeHandler.class), packageName); 329 Set<Class<? extends Class<?>>> handlerSet = resolverUtil.getClasses(); 330 for (Class<?> type : handlerSet) { 331 //Ignore inner classes and interfaces (including package-info.java) and abstract classes 332 if (!type.isAnonymousClass() && !type.isInterface() && !Modifier.isAbstract(type.getModifiers())) { 333 register(type); 334 } 335 } 336 } 337 338 // get information 339 340 /** 341 * 通過configuration對象可以獲取已註冊的所有typeHandler 342 */ 343 public Collection<TypeHandler<?>> getTypeHandlers() { 344 return Collections.unmodifiableCollection(ALL_TYPE_HANDLERS_MAP.values()); 345 } 346 347 }
由源碼可以看到， mybatis為我們實現了那麽多TypeHandler, 隨便打開一個TypeHandler，看其源碼，都可以看到，它繼承自一個抽象類：BaseTypeHandler，
那麽我們是不是也能通過繼承BaseTypeHandler，從而實現自定義的TypeHandler ?
答案是肯定的， 那麽現在下面就為大家演示一下自定義TypeHandler: =自定義TypeHandler分割線========
ExampleTypeHandler:
1 @MappedJdbcTypes(JdbcType.VARCHAR) 2 //此處如果不用註解指定jdbcType, 那麽，就可以在配置文件中通過"jdbcType"屬性指定， 同理， javaType 也可通過 @MappedTypes指定 3 public class ExampleTypeHandler extends BaseTypeHandler<String> { 4 5 @Override 6 public void setNonNullParameter(PreparedStatement ps, int i, String parameter, JdbcType jdbcType) throws SQLException { 7 ps.setString(i, parameter); 8 } 9 10 @Override 11 public String getNullableResult(ResultSet rs, String columnName) throws SQLException { 12 return rs.getString(columnName); 13 } 14 15 @Override 16 public String getNullableResult(ResultSet rs, int columnIndex) throws SQLException { 17 return rs.getString(columnIndex); 18 } 19 20 @Override 21 public String getNullableResult(CallableStatement cs, int columnIndex) throws SQLException { 22 return cs.getString(columnIndex); 23 } 24 }
然後，就該配置我們的自定義TypeHandler了：
1 <configuration> 2 <typeHandlers> 3 <!-- 由於自定義的TypeHandler在定義時已經通過註解指定了jdbcType, 所以此處不用再配置jdbcType --> 4 <typeHandler handler="ExampleTypeHandler"/> 5 </typeHandlers> 6 7 ...... 8 9 </configuration>
也就是說，我們在自定義TypeHandler的時候，可以在TypeHandler通過@MappedJdbcTypes指定jdbcType, 通過 @MappedTypes 指定javaType, 如果沒有使用註解指定，那麽我們就需要在配置文件中配置。
預知後事如何，請聽下回分解。
Mybatis 系列5