在实际项目中，geojson格式的文件应用场景非常多，比如：shapefile转geojson，加载geojson数据到openlayers、leaflet等开源地图组件中 等，还有些情况下需要自己把一系列点生成面，然后把面再转成geojson，之后把生成的geojson格式文件提供给前端使用，这里以java为例，实现坐标点生成geojson格式的Polygon文件。

        首先引入geotools相关jar包

<!-- geojson -->
    <dependency>
        <groupId>org.geotools</groupId>
	    <artifactId>gt-geojson</artifactId>
	    <version>23.2</version>
    </dependency>
<!-- 项目的pom文件中要引入包含geotools相关jar的仓库地址，不然geotools的jar包可能会拉取不下来 -->
	<repositories>
		<repository>  
            <id>alimaven</id>  
            <name>aliyun maven</name>  
            <url>http://maven.aliyun.com/nexus/content/groups/public/</url>  
            <releases>  
                <enabled>true</enabled>  
            </releases>  
            <snapshots>  
                <enabled>false</enabled>  
            </snapshots>  
        </repository>
        <repository>
			<id>osgeo-release</id>
			<name>Open Source Geospatial Foundation Repository</name>
			<url>https://repo.osgeo.org/repository/release/</url>
		</repository>
		<repository>
			<snapshots>
				<enabled>true</enabled>
			</snapshots>
			<id>boundless</id>
			<name>Boundless Maven Repository</name>
			<url>https://repo.boundlessgeo.com/main/</url>
		</repository>
		<repository>
			<id>osgeo</id>
			<name>Open Source Geospatial Foundation Repository</name>
			<url>http://download.osgeo.org/webdav/geotools/</url>
		</repository>
		<repository>
			<id>maven2-repository.dev.java.net</id>
			<name>Java.net repository</name>
			<url>http://download.java.net/maven/2</url>
		</repository>
	</repositories>

新建一个点数据转geojson格式的ploygon的类

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.StringWriter;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.List;

import org.geotools.feature.simple.SimpleFeatureBuilder;
import org.geotools.feature.simple.SimpleFeatureTypeBuilder;
import org.geotools.geojson.feature.FeatureJSON;
import org.geotools.referencing.crs.DefaultGeographicCRS;
import org.locationtech.jts.geom.Coordinate;
import org.locationtech.jts.geom.GeometryFactory;
import org.locationtech.jts.geom.MultiPolygon;
import org.locationtech.jts.geom.Polygon;
import org.opengis.feature.simple.SimpleFeature;
import org.opengis.feature.simple.SimpleFeatureType;

public class File2Geojson {

	public static void main(String[] args) throws IOException {
		//读取坐标点文件
		//文件格式如下：104.048574,30.752506;104.050062,30.751254;104.050801,30.750952|104.08962,30.670089;104.08684,30.665675;104.086489,30.665157|104.059962,30.647005;104.06156,30.649142;104.062694,30.650745;104.063921,30.652742
		//格式说明：符号 | 用来分割不同的Polygon  
		//        符号 ; 分割不同的坐标点
		//        符号 , 分割经纬度,前面为经度，后面为纬度
		File file = new File("C:\\Users\\Administrator\\Desktop\\log\\zuobiao.txt");

		FileInputStream inputStream = new FileInputStream(file);
		int length = inputStream.available();
		byte bytes[] = new byte[length];
		inputStream.read(bytes);
		inputStream.close();
		String str = new String(bytes, StandardCharsets.UTF_8);

		String[] polygonPointArr = str.split("\\|");
		//创建Polygon
		Polygon[] polygons=new Polygon[polygonPointArr.length];
		for (int i = 0; i < polygonPointArr.length; i++) {

			System.out.println("第" + (i + 1) + "个");
			String[] pointArr = polygonPointArr[i].split(";");

			List<Coordinate> polygonCoordinateList = new ArrayList<>();
			for (int j = 0; j < pointArr.length; j++) {
				String pointStr = pointArr[j];
				String[] point = pointStr.split(",");
				polygonCoordinateList.add(new Coordinate(Double.parseDouble(point[0]), Double.parseDouble(point[1])));
			}
			polygons[i] = new GeometryFactory().createPolygon(polygonCoordinateList.toArray(new Coordinate[0]));
		}
		//将Polygon数组转换成MultiPolygon
		MultiPolygon multiPolygon = new GeometryFactory().createMultiPolygon(polygons);
		//创建要素类
		SimpleFeatureTypeBuilder builder = new SimpleFeatureTypeBuilder();
		builder.setName("geometry");
		builder.setCRS(DefaultGeographicCRS.WGS84);
		builder.add("the_geom", multiPolygon.getClass());
		final SimpleFeatureType TYPE = builder.buildFeatureType();

		SimpleFeatureBuilder featureBuilder = new SimpleFeatureBuilder(TYPE);
		featureBuilder.add(multiPolygon);
		SimpleFeature feature = featureBuilder.buildFeature(null);
		//将要素类转换成geojson
		FeatureJSON fjson = new FeatureJSON();
		StringWriter writer = new StringWriter();
		fjson.writeFeature(feature, writer);
		String geojson = writer.toString();
		//输出geojson字符串到文件中
		FileOutputStream fos = new FileOutputStream("C:\\Users\\Administrator\\Desktop\\log\\chengdu.json");
        fos.write(geojson.getBytes());
        fos.close();
        System.out.println("完成");
	}

}

我们打开可以查看geojson格式文件的工具：

http://tool.tooleek.com/tools/mapshaper

选择生成好的geojson格式的文件，打开就可以看到下面的效果

geojson格式文件成功生成，并能提供给前端使用，前端也可以显示到地图上