MyBatis使用别名

<typeAliases>
<!--
通过package, 可以直接指定package的名字， mybatis会自动扫描你指定包下面的javabean,
并且默认设置一个别名，默认的名字为： javabean 的首字母小写的非限定类名来作为它的别名。
也可在javabean 加上注解@Alias 来自定义别名， 例如： @Alias(user)
<package name="cn.itcast.mybatis.po"/>
-->
<typeAlias alias="user" type="cn.itcast.mybatis.po.User"/>
</typeAliases>

package org.apache.ibatis.type;

import java.math.BigDecimal;
import java.math.BigInteger;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Date;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Set;

import org.apache.ibatis.io.ResolverUtil;
import org.apache.ibatis.io.Resources;

public class TypeAliasRegistry {

private final Map<String, Class<?>> TYPE_ALIASES = new HashMap<String, Class<?>>();

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

registerAlias("byte", Byte.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("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("_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("_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);
}

@SuppressWarnings("unchecked")
// throws class cast exception as well if types cannot be assigned
public <T> Class<T> resolveAlias(String string) {
try {
if (string == null) return null;
String key = string.toLowerCase(Locale.ENGLISH); // issue #748
Class<T> value;
if (TYPE_ALIASES.containsKey(key)) {
value = (Class<T>) TYPE_ALIASES.get(key);
} else {
value = (Class<T>) Resources.classForName(string);
}
return value;
} catch (ClassNotFoundException e) {
throw new TypeException("Could not resolve type alias '" + string + "'.  Cause: " + e, e);
}
}

public void registerAliases(String packageName){
registerAliases(packageName, Object.class);
}

public void registerAliases(String packageName, Class<?> superType){
ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<Class<?>>();
resolverUtil.find(new ResolverUtil.IsA(superType), packageName);
Set<Class<? extends Class<?>>> typeSet = resolverUtil.getClasses();
for(Class<?> type : typeSet){
// Ignore inner classes and interfaces (including package-info.java)
// Skip also inner classes. See issue #6
if (!type.isAnonymousClass() && !type.isInterface() && !type.isMemberClass()) {
registerAlias(type);
}
}
}

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

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

public void registerAlias(String alias, String value) {
try {
registerAlias(alias, Resources.classForName(value));
} catch (ClassNotFoundException e) {
throw new TypeException("Error registering type alias "+alias+" for "+value+". Cause: " + e, e);
}
}

/**
* @since 3.2.2
*/
public Map<String, Class<?>> getTypeAliases() {
return Collections.unmodifiableMap(TYPE_ALIASES);
}

}