环境

mybatis ：1.3.4-mybatis-spring-boot-starter
postgresql: 12.16
jdk:8+

mapper.java

@Mapper
public interface CustomMapper {

    @Options(statementType = StatementType.CALLABLE)
    @Select("CALL pg_schema.sync_area_code(#{out_result, mode=IN, jdbcType=VARCHAR})")
    String syncAreaCode(@Param("out_result") String outResult);

}

此处@Param参数要和#{out_result, 一致

测试方法

@ExtendWith(SpringExtension.class)
@SpringBootTest(classes = DemoApplication.class)
public class TestCode {

    @Autowired
    private CustomMapper customMapper;
   @Test
    public void testMybatis() {
        String outResult = "成功2333！";

       customMapper.syncAreaCode(outResult);
        System.out.println(outResult);
    }
}

存储过程

-- DROP PROCEDURE sync_area_code(inout varchar);

CREATE OR REPLACE PROCEDURE sync_area_code(INOUT out_result character varying)
 LANGUAGE plpgsql
AS $procedure$
begin
    
    -- 业务逻辑

    out_result := '成功！';

exception
    when others then
        rollback;
end;
$procedure$
;