MyBatis 擴(kuò)展BaseTypeHandler 轉(zhuǎn)換泛型 JSON 列表的解決方法

更新時間：2025年12月18日 08:48:04 作者：Milton

本文詳細(xì)介紹了MyBatis中處理JSON轉(zhuǎn)換的bug及其解決方法,文章還介紹了如何處理抽象類和自定義對象的JSON轉(zhuǎn)換,并提供了一個基類AbstractListTypeHandler作為示例,最后,文章附上了MyBatis內(nèi)建的javaTypeAlias鏈接,感興趣的朋友跟隨小編一起看看吧

一. 對象JSON轉(zhuǎn)換

這個是比較簡單的情況, 有通用的處理方法, 例如

用Jackson實現(xiàn)一個通用的 TypeHandler

@Slf4j
public class JacksonTypeHandler<T> extends BaseTypeHandler<T> {
private static ObjectMapper OBJECT_MAPPER;
private final Class<T> clazz;
public JacksonTypeHandler(Class<T> clazz) {
if (log.isTraceEnabled()) {
log.trace("JacksonTypeHandler[{}]", clazz);
}
this.clazz = clazz;
}
@Override
public void setNonNullParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException {
ps.setString(i, toJson(parameter));
}
@Override
public T getNullableResult(ResultSet rs, String columnName) throws SQLException {
return parse(rs.getString(columnName));
}
@Override
public T getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
return parse(rs.getString(columnIndex));
}
@Override
public T getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
return parse(cs.getString(columnIndex));
}
protected T parse(String json) {
if (json == null || json.isEmpty()) return null;
try {
return getObjectMapper().readValue(json, clazz);
} catch (IOException e) {
throw new RuntimeException(e);
}
}
protected String toJson(T obj) {
try {
return getObjectMapper().writeValueAsString(obj);
} catch (JsonProcessingException e) {
throw new RuntimeException(e);
}
}
private static ObjectMapper getObjectMapper() {
if (null == OBJECT_MAPPER) {
OBJECT_MAPPER = new ObjectMapper();
OBJECT_MAPPER.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
}
return OBJECT_MAPPER;
}
}

使用時直接指定 typeHandler 就行

<result property="groupFilter" column="group_filter" typeHandler="com.somewhere.mybatis.JacksonTypeHandler"/>

以及

#{groupFilter, typeHandler=com.somewhere.mybatis.JacksonTypeHandler},

二. 列表JSON Array轉(zhuǎn)換

字段中更常見的是 List 類型的JSON Array結(jié)構(gòu), 這種情況通過擴(kuò)展 BaseTypeHandler 沒有通用的處理方法, 有兩種實現(xiàn)途徑

通用的TypeHandler, 需要指定javaType

用 Jackson 實現(xiàn)一個通用的 TypeHandler, 注意構(gòu)造函數(shù)中的 clazz, 如果不指定, 在默認(rèn)情況下 mybatis 傳進(jìn)來的是一個不帶泛型參數(shù)的 List

@Slf4j
public class JacksonListTypeHandler<T> extends BaseTypeHandler<List<T>> {
private static ObjectMapper OBJECT_MAPPER;
private final TypeReference<List<T>> type;
public JacksonListTypeHandler(Class<T> clazz) {
log.info("JacksonListTypeHandler[{}]", clazz);
this.type = new TypeReference<>() {
@Override
public Type getType() {
// 返回參數(shù)化類型 List<T>
return new ParameterizedType() {
@Override
public Type[] getActualTypeArguments() {
return new Type[]{clazz};
}
@Override
public Type getRawType() {
return List.class;
}
@Override
public Type getOwnerType() {
return null;
}
};
}
};
}
@Override
public void setNonNullParameter(PreparedStatement ps, int i, List<T> parameter, JdbcType jdbcType) throws SQLException {
ps.setString(i, toJson(parameter));
}
@Override
public List<T> getNullableResult(ResultSet rs, String columnName) throws SQLException {
return parse(rs.getString(columnName));
}
@Override
public List<T> getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
return parse(rs.getString(columnIndex));
}
@Override
public List<T> getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
return parse(cs.getString(columnIndex));
}
private List<T> parse(String json) {
if (json == null || json.isEmpty()) return null;
try {
return getObjectMapper().readValue(json, type);
} catch (IOException e) {
throw new RuntimeException(e);
}
}
protected String toJson(List<T> obj) {
try {
return getObjectMapper().writeValueAsString(obj);
} catch (JsonProcessingException e) {
throw new RuntimeException(e);
}
}
public static ObjectMapper getObjectMapper() {
if (null == OBJECT_MAPPER) {
OBJECT_MAPPER = new ObjectMapper();
OBJECT_MAPPER.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
}
return OBJECT_MAPPER;
}
}

除了用 TypeReference, 還可以用 JavaType

@Slf4j
public class ListJacksonTypeHandler<T> extends BaseTypeHandler<List<T>> {
private final JavaType type;
public ListJacksonTypeHandler(Class<T> clazz) {
log.info("ListJacksonTypeHandler[{}]", clazz);
// 創(chuàng)建 List<T> 類型的 JavaType
this.type = JacksonUtil.getObjectMapper()
.getTypeFactory()
.constructCollectionType(List.class, clazz);
}
// 其它一樣
}

需要在 mapper 中強(qiáng)制指定javaType, 如果是MyBatis自帶的簡單類型, 可以直接用 alias(見下面的表格), 如果是自定義的對象, 則需要用對象類的完整包路徑

<result property="ips" column="ips" javaType="string" typeHandler="com.somewhere.mybatis.JacksonListTypeHandler"/>

以及

#{users,javaType=string,typeHandler=com.somewhere.mybatis.JacksonListTypeHandler},

這樣啟動后, 如果初始化的type是正確的string 才能正確解析

2025-12-15T10:33:42.896+08:00 INFO 1 --- [some-service] [main] c.somewhere.mybatis.JacksonListTypeHandler: JacksonListTypeHandler[class java.lang.String]

抽象類, 根據(jù)對象類型實現(xiàn)具體的 TypeHandler

如果不在 mapper 中指定類型, 就需要在 TypeHandler 中指定, 這樣就不是通用的了

寫一個基類 AbstractListTypeHandler

@Slf4j
public abstract class AbstractListTypeHandler<T> extends BaseTypeHandler<List<T>> {
private static ObjectMapper OBJECT_MAPPER;
@Override
public void setNonNullParameter(PreparedStatement ps, int i, List<T> parameter, JdbcType jdbcType) throws SQLException {
ps.setString(i, toJson(parameter));
}
@Override
public List<T> getNullableResult(ResultSet rs, String columnName) throws SQLException {
return parse(rs.getString(columnName));
}
@Override
public List<T> getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
return parse(rs.getString(columnIndex));
}
@Override
public List<T> getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
return parse(cs.getString(columnIndex));
}
protected List<T> parse(String json) {
if (json == null || json.isEmpty()) return null;
try {
return getObjectMapper().readValue(json, specificType());
} catch (IOException e) {
throw new RuntimeException(e);
}
}
protected String toJson(List<T> obj) {
try {
return getObjectMapper().writeValueAsString(obj);
} catch (JsonProcessingException e) {
throw new RuntimeException(e);
}
}
private static ObjectMapper getObjectMapper() {
if (null == OBJECT_MAPPER) {
OBJECT_MAPPER = new ObjectMapper();
OBJECT_MAPPER.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
}
return OBJECT_MAPPER;
}
protected abstract TypeReference<List<T>> specificType();
}

根據(jù)具體的使用場景, 創(chuàng)建對應(yīng)的實現(xiàn)類

public class ListLongTypeHandler extends AbstractListTypeHandler<Long> {
@Override
protected TypeReference<List<Long>> specificType() {
return new TypeReference<>() {};
}
}

使用時, 直接用 typeHandler 指定, 不需要指定類型

#{setIds, typeHandler=com.somewhere.mybatis.ListLongTypeHandler},
...
@Result(column="set_ids", property="setIds", typeHandler= ListLongTypeHandler.class),

附: MyBatis 內(nèi)建的 javaType Alias

鏈接: https://mybatis.org/mybatis-3/configuration.html#typeAliases

alias	javaType
_byte	byte
_char (since 3.5.10)	char
_character (since 3.5.10)	char
_long	long
_short	short
_int	int
_integer	int
_double	double
_float	float
_boolean	boolean
string	String
byte	Byte
char (since 3.5.10)	Character
character (since 3.5.10)	Character
long	Long
short	Short
int	Integer
integer	Integer
double	Double
float	Float
boolean	Boolean
date	Date
decimal	BigDecimal
bigdecimal	BigDecimal
biginteger	BigInteger
object	Object
date[]	Date[]
decimal[]	BigDecimal[]
bigdecimal[]	BigDecimal[]
biginteger[]	BigInteger[]
object[]	Object[]
map	Map
hashmap	HashMap
list	List
arraylist	ArrayList
collection	Collection
iterator	Iterator