[英]How can you insert GeoJSON polygon into PostGIS using Java JDBC PreparedStatement placeholder?
如果您使用的是JavaScript库“ Leaflet”及其插件“ Draw”,则可以检索geojson,如下所示:
{
"type" : "Polygon",
"coordinates" : [ [ [ 13.95938491821289, 53.41329518072117 ], [ 14.955865859985348, 54.412618223375205 ], [ 13.9606294631958, 54.4120067663998 ], [ 13.95938491821289, 53.41329518072117 ] ] ]
}
如果您如上所述将json发送到网络服务器(带有Java代码,例如Play Framework),那么我想知道在不使用字符串串联创建sql字符串的情况下,将其插入或更新到postgis数据库中的最简单方法。 实际上,它可以使用上述结构创建SQL字符串,但是您要避免字符串串联,这是我关于如何改为使用PreparedStatement占位符的问题的原因。 例如,可以从pgAdmin直接执行以下SQL代码(也可以通过JDBC代码):
UPDATE polygons
SET
geom = ST_SetSRID(ST_GeomFromGeoJSON
('{
"type" : "Polygon",
"coordinates" : [ [ [ 13.95938491821289, 53.41329518072117 ], [ 14.955865859985348, 54.412618223375205 ], [ 13.9606294631958, 54.4120067663998 ], [ 13.95938491821289, 53.41329518072117 ] ] ]
}'), 26918)
WHERE polygonid = 1;
但是,正如大多数开发人员所了解的那样,我们应该避免String串联,而应使用占位符,例如,如果使用PreparedStatement(或者如果使用Spring Framework,则为JdbcTemplate)。
下面是一些代码,说明了什么在起作用,什么在不起作用。
我正在使用的PostGIS数据库表是通过以下语句创建的:
CREATE TABLE polygons (
polygonid serial NOT NULL,
geom geometry(Polygon,26918),
CONSTRAINT polygon_pkey PRIMARY KEY (polygonid)
);
在我的Maven文件pom.xml中,我正在使用此依赖项:
<dependency>
<groupId>net.postgis</groupId>
<artifactId>postgis-jdbc</artifactId>
<version>2.2.0</version>
</dependency>
Java代码:
import java.sql.*;
import org.postgis.PGgeometry;
...
// For verbosity reasons, I am below not including
// any try/catch/throw statements or any closings of connections/statements/recordsets
String url = "jdbc:postgresql://localhost:5432/nameOfYourDatabase";
Connection connection = DriverManager.getConnection(url, "postgres", "[YOUR_PASSWORD]");
// First below is some SQL query code which works and thus
// proves that the setup with jar files and database connection indeed works:
long maxPolygonId = 100L;
PreparedStatement ps = connection.prepareStatement(
"SELECT polygonid , geom FROM polygons WHERE polygonid < ?"
);
ps.setLong(1, maxPolygonId);
ResultSet rs = ps.executeQuery();
while(rs.next()) {
long polygonId = rs.getLong(1);
// Actually it works to use PGgeometry as below WITHOUT first having to do
// "((org.postgresql.PGConnection)conn).addDataType("geometry",Class.forName("org.postgis.PGgeometry"));"
// as currently documented at http://postgis.net/docs/ch06.html#idp48666800
PGgeometry geom = (PGgeometry)rs.getObject(2);
System.out.println("polygonId: " + polygonId);
System.out.println("geom: " + geom); // e.g. "geom: SRID=26918;POLYGON((17.9661226272583 59.41375375704178, ... ,17.9661226272583 59.41375375704178))"
}
// Below is some code that also indeed works fine but it uses string
// concatenation for the json string instead of placeholder which I want to use instead
String geoJson =
" { " +
" \"type\" : \"Polygon\", " +
" \"coordinates\" : [ [ [ 13.95938491821289, 53.41329518072117 ], [ 14.955865859985348, 54.412618223375205 ], [ 13.9606294631958, 54.4120067663998 ], [ 13.95938491821289, 53.41329518072117 ] ] ] " +
" } ";
String sqlUpdatingWithGeoJson =
" UPDATE polygons " +
" SET " +
" geom = ST_SetSRID(ST_GeomFromGeoJSON " +
" (' " +
geoJson +
" '), 26918) " +
" WHERE polygonid = ? ";
long idForPolygonToUpdate = 1L;
ps = connection.prepareStatement(sqlUpdatingWithGeoJson);
ps.setLong(1, idForPolygonToUpdate);
ps.executeUpdate();
// Below is some code which does NOT work when I am trying
// to use placeholder instead of string concatenation as above
String sqlUpdatingWithGeoJsonAsPlaceHolder =
" UPDATE polygons " +
" SET " +
" geom = ST_SetSRID(ST_GeomFromGeoJSON " +
" (' " +
" ? " + // NOTE that this line is the difference with the sql update string above !
" '), 26918) " +
" WHERE polygonid = ? ";
ps = connection.prepareStatement(sqlUpdatingWithGeoJsonAsPlaceHolder);
ps.setString(1, geoJson);
ps.setLong(2, idForPolygonToUpdate);
// The above row results in the exception below
// org.postgresql.util.PSQLException: The column index is out of range: 2, number of columns: 1.
ps.executeUpdate();
// Below I instead tried to replace the whole expression as a string to be set
// through the placeholder but it does NOT work neither
String geomValue =
" ST_SetSRID(ST_GeomFromGeoJSON " +
" (' " +
geoJson +
" '), 26918) ";
String sqlUpdatingWithPostGisStatementForPlaceHolder =
" UPDATE polygons " +
" SET " +
" geom = ? " +
" WHERE polygonid = ? ";
ps = connection.prepareStatement(sqlUpdatingWithPostGisStatementForPlaceHolder);
ps.setString(1, geomValue); // I have also tried setObject instead of setString here
ps.setLong(2, idForPolygonToUpdate);
// The above row also results in the same exception as previous above i.e. below exception:
// org.postgresql.util.PSQLException: The column index is out of range: 2, number of columns: 1.
ps.executeUpdate();
也许解决方案可能是将json字符串转换为PostGIS / PostgreSQL JDBC驱动程序可以理解的Java对象,然后使用方法“ prepareStatement.setObject”,但是该Java对象应使用什么类型以及如何使用您轻松将json字符串转换为此类对象?
String sqlUpdatingWithGeoJsonAsPlaceHolder =
" UPDATE polygons " +
" SET " +
" geom = ST_SetSRID(ST_GeomFromGeoJSON(?), 26918) " +
" WHERE polygonid = ? ";
ps = connection.prepareStatement(sqlUpdatingWithGeoJsonAsPlaceHolder);
ps.setString(1, geoJson);
ps.setLong(2, idForPolygonToUpdate);
ps.executeUpdate();
这应该可行:您将geojson作为字符串传递。 函数ST_GeomFromGeoJSON将字符串作为第一个参数,因此可以准备和执行该语句。
您收到该错误是因为您引用了问号。 这样,问号不会被解释为占位符!
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