基于Mybatis-Plus实现Geometry字段在PostGis空间数据库中的使用

背景

在OGC标准中，通常空间字段是由Geometry类型来表示。而一般编程语言中是没有这种数据类型的。以java为例，怎么操作这些数据，满足业务需求呢？跟着本文一起来学习吧。

今天介绍基于postgis-jdbc的geometry属性的操作。

一、在pom.xml中引入postgis-jdbc相关jar包

<!-- PostgreSql 驱动包 add by wuzuhu on 2022-08-16 -->
<dependency>
    <groupId>net.postgis</groupId>
    <artifactId>postgis-jdbc</artifactId>
    <version>2.5.0</version>
</dependency>

二、需要自定义Handler类来扩展字段支持。

package com.hngtghy.framework.handler;
 
import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
 
import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;
import org.apache.ibatis.type.MappedTypes;
import org.postgis.Geometry;
import org.postgis.PGgeometry;
 
@MappedTypes({String.class})
public class PgGeometryTypeHandler extends BaseTypeHandler<String> {
 
    @Override
    public void setNonNullParameter(PreparedStatement ps, int i, String parameter, JdbcType jdbcType) throws SQLException {
        PGgeometry pGgeometry = new PGgeometry(parameter);
        Geometry geometry = pGgeometry.getGeometry();
        geometry.setSrid(4326);
        ps.setObject(i, pGgeometry);
    }
 
    @Override
    public String getNullableResult(ResultSet rs, String columnName) throws SQLException {
        String string = rs.getString(columnName);
        return getResult(string);
    }
 
    @Override
    public String getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
        String string = rs.getString(columnIndex);
        return getResult(string);
    }
 
    @Override
    public String getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
        String string = cs.getString(columnIndex);
        return getResult(string);
    }
 
 
    private String getResult(String string) throws SQLException {
        PGgeometry pGgeometry = new PGgeometry(string);
        String s = pGgeometry.toString();
        return s.replace("SRID=4326;", "");
    }
}

注意，在getResult()中关于4326坐标系的定义，可以根据需要进行废弃。这里写上为了统一投影坐标系。

三、在数据中创建表，建表语句如下：

create table biz_point_test(
    id int8 primary key,
    name varchar(100),
    geom geometry(Point,4326)
);

四、定义Mybatis-plus实体

package com.hngtghy.project.extend.student.domain;
 
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import com.hngtghy.framework.handler.PgGeometryTypeHandler;
 
import lombok.AllArgsConstructor;
import lombok.Getter;
import lombok.NoArgsConstructor;
import lombok.Setter;
import lombok.ToString;
 
@TableName(value ="biz_point_test",autoResultMap = true)
@NoArgsConstructor
@AllArgsConstructor
@Setter
@Getter
@ToString
public class PointTest {
 
    @TableId
    private Long id;
    
    private String name;
    
    @TableField(typeHandler = PgGeometryTypeHandler.class)
    private String geom;
    
    @TableField(exist=false)
    private String geomJson;
}

提醒：1、在属性上使用@TableField(typeHandler=xxx)来指定对应的类型转换器。2、需要在实体上定义autoResultMap=true。否则配置不一定生效。

五、定义mapper查询器

package com.hngtghy.project.extend.student.mapper;
 
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;
 
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.hngtghy.project.extend.student.domain.PointTest;
 
public interface PointTestMapper extends BaseMapper<PointTest>{
 
    static final String FIND_GEOJSON_SQL="<script>"
            + "select st_asgeojson(geom) as geomJson from biz_point_test "
            + "where id = #{id} "
            + "<if test='null != name'>and p.name like concat('%', #{name}, '%')</if>"
            + "</script>";
    @Select(FIND_GEOJSON_SQL)
    PointTest findGeoJsonById(@Param("id")Long id,@Param("name")String name);
    
}

六、定义service业务类

package com.hngtghy.project.extend.student.service.impl;
 
import java.util.List;
 
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
 
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.hngtghy.project.extend.student.domain.PointTest;
import com.hngtghy.project.extend.student.mapper.PointTestMapper;
import com.hngtghy.project.extend.student.service.IPointTestService;
 
@Service
public class PointTestServcieImpl extends ServiceImpl<PointTestMapper, PointTest> implements IPointTestService{
 
    @Autowired
    private PointTestMapper pointMapper;
    
    @Override
    public PointTest selectById(Long id) {
        return pointMapper.selectById(id);
    }
 
    @Override
    public List<PointTest> selectList(PointTest point) {
        QueryWrapper<PointTest> queryWrapper = new QueryWrapper<PointTest>();
        queryWrapper.select("id,name");
        return this.getBaseMapper().selectList(queryWrapper);
    }
 
    @Override
    public int insertPointTest(PointTest point) {
        return pointMapper.insert(point);
    }
 
    @Override
    public int updatePoint(PointTest point) {
        return pointMapper.updateById(point);
    }
 
    @Override
    public PointTest selectGeomById(Long id) {
        QueryWrapper<PointTest> queryWrapper = new QueryWrapper<PointTest>();
        queryWrapper.select("geom","st_asgeojson(geom) as geomJson");
        queryWrapper.eq("id", id);
        return this.getBaseMapper().selectOne(queryWrapper);
    }
 
    @Override
    public PointTest findGeoJsonById(Long id) {
        return pointMapper.findGeoJsonById(id, null);
    }
 
}

这里添加了一个数据库不存在的字段geomJson,会将空间属性转变成geojson字段，方便于前台的如leaflet、openlayers、cesium等组件进行展示。所以使用postgis的st_asgeojson（xxx）进行函数转换。

七、相关方法调用

//1、列表查询
List<PointTest> pointList = pointService.selectList(null);
System.out.println(pointList);

[PointTest(id=1559371184090423297, name=中寨居委会, geom=null, geomJson=null), PointTest(id=2, name=禾滩村, geom=null, geomJson=null), PointTest(id=1559403683801796610, name=中寨居委会, geom=null, geomJson=null)]

//2、插入
PointTest point = new PointTest();
point.setName("中寨居委会");
point.setGeom("POINT(109.262605 27.200669)");//POINT(lng,lat) 经度,纬度
pointService.insertPointTest(point);

//3、查询数据
 PointTest point = pointService.selectGeomById(1559371184090423297L);
 PointTest json = pointService.findGeoJsonById(1559371184090423297L);

PointTest(id=null, name=null, geom=POINT(109.262605 27.200669), geomJson={"type":"Point","coordinates":[109.262605,27.200669]})
PointTest(id=null, name=null, geom=null, geomJson={"type":"Point","coordinates":[109.262605,27.200669]})

八、使用pgadmin可以查看到相应的点数据，如下图所示：

总结：通过以上步骤可以实现在mybatis-plus中操作geometry空间字段，同时实现查询和插入操作。通过geojson，结合前端可视化组件即可完成矢量数据的空间可视化。