一、前提概要

1.1 支持环境

数据库支持：MySql版本要求 5.7+

1.2 需求场景

使用MySQL数据库存储时，由于业务要求实体类中特定字段需要使用 自定义类型或者List、Map类型。

二、需求实现

2.1 非自定义数据类型，List、Map

首先：在需要转换的实体类字段上加上：

@TableField(typeHandler = JacksonTypeHandler.class)

接着：在该实体类上修改 @TableName

@TableName(value = "数据库表名",autoResultMap = true)

2.2 自定义类型数据类型

引入依赖：

<properties>
 <jackson-core.version>2.12.6</jackson-core.version>
 <jackson-databind.version>2.12.7.1</jackson-databind.version>
 <jackson-annotations.version>2.15.2</jackson-annotations.version>
</properties>

 <dependency>
   <groupId>com.fasterxml.jackson.core</groupId>
   <artifactId>jackson-core</artifactId>
   <version>${jackson-core.version}</version>
 </dependency>
 <dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>${jackson-databind.version}</version>
 </dependency>
 <dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-annotations</artifactId>
    <version>${jackson-annotations.version}</version>
</dependency>

首先定义数据处理工具类：

@Component
public class ObjectToJackson {
    private static ObjectMapper mapper;

    @Resource
    public void setMapper(ObjectMapper mapper) {
        ObjectToJackson.mapper = mapper;
    }

    public static <T> String objectToJson(T o) {
        try {
            return ObjectToJackson.mapper.writeValueAsString(o);
        } catch (Exception e) {
            e.printStackTrace();
            throw new ServerException(500);
        }
    }

    public static <T> T jsonToObject(String s, TypeReference<T> typeReference) {
        if (s == null) {
            return null;
        }
        try {
            return ObjectToJackson.mapper.readValue(s, typeReference);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
            throw new ServerException(500);
        }
    }
}

接着定义自己的转化规则：

public class ObjectToJacksonHandler extends BaseTypeHandler<Object> {

    @Override
    public void setNonNullParameter(PreparedStatement ps, int i, Object parameter, JdbcType jdbcType) throws SQLException {
        String json = ObjectToJackson.objectToJson(parameter);
        ps.setString(i, json);
    }

    @Override
    public Object getNullableResult(ResultSet rs, String columnName) throws SQLException {
        String string = rs.getString(columnName);
        return ObjectToJackson.jsonToObject(string, new TypeReference<>() {
        });
    }

    @Override
    public Object getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
        String string = rs.getString(columnIndex);
        return ObjectToJackson.jsonToObject(string, new TypeReference<>() {
        });
    }

    @Override
    public Object getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
        String string = cs.getString(columnIndex);
        return ObjectToJackson.jsonToObject(string, new TypeReference<>() {
        });
    }
}

使用：

@TableName(value = "数据库表名", autoResultMap = true)

@TableField(typeHandler = ObjectToJacksonHandler.class)