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@ToStringpublic 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; @Servicepublic 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。
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