MyBatis-02-别名

别名

TypeAliasRegistry

默认注册了很多别名，构造函数注册的

public TypeAliasRegistry() {
  registerAlias("string", String.class);

  registerAlias("byte", Byte.class);
  registerAlias("char", Character.class);
  registerAlias("character", Character.class);
  registerAlias("long", Long.class);
  registerAlias("short", Short.class);
  registerAlias("int", Integer.class);
  registerAlias("integer", Integer.class);
  registerAlias("double", Double.class);
  registerAlias("float", Float.class);
  registerAlias("boolean", Boolean.class);

  registerAlias("byte[]", Byte[].class);
  registerAlias("char[]", Character[].class);
  registerAlias("character[]", Character[].class);
  registerAlias("long[]", Long[].class);
  registerAlias("short[]", Short[].class);
  registerAlias("int[]", Integer[].class);
  registerAlias("integer[]", Integer[].class);
  registerAlias("double[]", Double[].class);
  registerAlias("float[]", Float[].class);
  registerAlias("boolean[]", Boolean[].class);

  registerAlias("_byte", byte.class);
  registerAlias("_char", char.class);
  registerAlias("_character", char.class);
  registerAlias("_long", long.class);
  registerAlias("_short", short.class);
  registerAlias("_int", int.class);
  registerAlias("_integer", int.class);
  registerAlias("_double", double.class);
  registerAlias("_float", float.class);
  registerAlias("_boolean", boolean.class);

  registerAlias("_byte[]", byte[].class);
  registerAlias("_char[]", char[].class);
  registerAlias("_character[]", char[].class);
  registerAlias("_long[]", long[].class);
  registerAlias("_short[]", short[].class);
  registerAlias("_int[]", int[].class);
  registerAlias("_integer[]", int[].class);
  registerAlias("_double[]", double[].class);
  registerAlias("_float[]", float[].class);
  registerAlias("_boolean[]", boolean[].class);

  registerAlias("date", Date.class);
  registerAlias("decimal", BigDecimal.class);
  registerAlias("bigdecimal", BigDecimal.class);
  registerAlias("biginteger", BigInteger.class);
  registerAlias("object", Object.class);

  registerAlias("date[]", Date[].class);
  registerAlias("decimal[]", BigDecimal[].class);
  registerAlias("bigdecimal[]", BigDecimal[].class);
  registerAlias("biginteger[]", BigInteger[].class);
  registerAlias("object[]", Object[].class);

  registerAlias("map", Map.class);
  registerAlias("hashmap", HashMap.class);
  registerAlias("list", List.class);
  registerAlias("arraylist", ArrayList.class);
  registerAlias("collection", Collection.class);
  registerAlias("iterator", Iterator.class);

  registerAlias("ResultSet", ResultSet.class);
}

别名注册器
不只是 TypeAliasRegistry 自己注册了常用类型的别名，Configuration 也注册了一些自己需要的别名

public Configuration() {
  typeAliasRegistry.registerAlias("JDBC", JdbcTransactionFactory.class);
  typeAliasRegistry.registerAlias("MANAGED", ManagedTransactionFactory.class);

  typeAliasRegistry.registerAlias("JNDI", JndiDataSourceFactory.class);
  typeAliasRegistry.registerAlias("POOLED", PooledDataSourceFactory.class);
  typeAliasRegistry.registerAlias("UNPOOLED", UnpooledDataSourceFactory.class);

  typeAliasRegistry.registerAlias("PERPETUAL", PerpetualCache.class);
  typeAliasRegistry.registerAlias("FIFO", FifoCache.class);
  typeAliasRegistry.registerAlias("LRU", LruCache.class);
  typeAliasRegistry.registerAlias("SOFT", SoftCache.class);
  typeAliasRegistry.registerAlias("WEAK", WeakCache.class);

  typeAliasRegistry.registerAlias("DB_VENDOR", VendorDatabaseIdProvider.class);

  typeAliasRegistry.registerAlias("XML", XMLLanguageDriver.class);
  typeAliasRegistry.registerAlias("RAW", RawLanguageDriver.class);

  typeAliasRegistry.registerAlias("SLF4J", Slf4jImpl.class);
  typeAliasRegistry.registerAlias("COMMONS_LOGGING", JakartaCommonsLoggingImpl.class);
  typeAliasRegistry.registerAlias("LOG4J", Log4jImpl.class);
  typeAliasRegistry.registerAlias("LOG4J2", Log4j2Impl.class);
  typeAliasRegistry.registerAlias("JDK_LOGGING", Jdk14LoggingImpl.class);
  typeAliasRegistry.registerAlias("STDOUT_LOGGING", StdOutImpl.class);
  typeAliasRegistry.registerAlias("NO_LOGGING", NoLoggingImpl.class);

  typeAliasRegistry.registerAlias("CGLIB", CglibProxyFactory.class);
  typeAliasRegistry.registerAlias("JAVASSIST", JavassistProxyFactory.class);

  languageRegistry.setDefaultDriverClass(XMLLanguageDriver.class);
  languageRegistry.register(RawLanguageDriver.class);
}

别名会转小写

public void registerAlias(String alias, Class<?> value) {
  if (alias == null) {
    throw new TypeException("The parameter alias cannot be null");
  }
  // issue #748
  String key = alias.toLowerCase(Locale.ENGLISH);
  if (typeAliases.containsKey(key) && typeAliases.get(key) != null && !typeAliases.get(key).equals(value)) {
    throw new TypeException(
        "The alias '" + alias + "' is already mapped to the value '" + typeAliases.get(key).getName() + "'.");
  }
  typeAliases.put(key, value);
}

注解声明别名

public void registerAlias(Class<?> type) {
  String alias = type.getSimpleName();
  Alias aliasAnnotation = type.getAnnotation(Alias.class);
  if (aliasAnnotation != null) {
    alias = aliasAnnotation.value();
  }
  registerAlias(alias, type);
}

XMLConfigBuilder 字符串得到 Class 会使用别名
通过字符串解决类都会先在别名注册器查找看能不能找到

protected <T> Class<? extends T> resolveClass(String alias) {
  try {
    return alias == null ? null : resolveAlias(alias);
  } catch (Exception e) {
    throw new BuilderException("Error resolving class. Cause: " + e, e);
  }
}

protected <T> Class<? extends T> resolveAlias(String alias) {
  return typeAliasRegistry.resolveAlias(alias);
}

public <T> Class<T> resolveAlias(String string) {
  try {
    if (string == null) {
      return null;
    }
    // issue #748
    String key = string.toLowerCase(Locale.ENGLISH);
    Class<T> value;
	// 先别名获取, 看是否注册了别名
    if (typeAliases.containsKey(key)) {
      value = (Class<T>) typeAliases.get(key);
    } else {
	  // 没有注册别名就使用类全限定名
      value = (Class<T>) Resources.classForName(string);
    }
    return value;
  } catch (ClassNotFoundException e) {
    throw new TypeException("Could not resolve type alias '" + string + "'.  Cause: " + e, e);
  }
}