在 Java 运行时从 zip 文件中读取 ESRI shapefile - DataStoreFinder.getDataStore(connectParameters) 返回 null

Question

我们正在构建一个用于上传包含 ESRI 形状文件的 zip 文件的服务。该服务应该能够读取 shapefile 并对其内容进行处理。所以我构建了一个类，将 zip 文件解压缩到临时文件夹（System.getProperty("java.io.tmpdir") 的子文件夹）。

另一个类从 Unzip 类调用 unzip 方法，然后尝试使用 Geotools 读取解压后的 shapefile。它使用 Geotools DataStoreFinder.getDataStore(Map params) 方法从解压缩的 shapefile 创建数据存储。这里出现了问题：getDataStore 方法返回 null。我测试了网址，它看起来没问题。派生 URL 的文件存在，是一个文件，可以由应用程序读取（使用 shapefile.exists()、shapefile.isFile()、shapefile.canRead() 进行测试）。那么，有什么问题呢？为什么会返回 null？

这是（相关的）代码：

import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import org.geotools.data.DataStore;
import org.geotools.data.DataStoreFinder;
import org.geotools.data.FeatureSource;
import org.geotools.feature.FeatureCollection;
import org.geotools.feature.FeatureIterator;
import org.opengis.feature.simple.SimpleFeature;
import org.opengis.feature.simple.SimpleFeatureType;

import com.geodan.equus.entity.dataset.BasicFeature;
import com.geodan.equus.exception.EquusException;
import com.geodan.equus.processor.EquusProcessor;
import com.geodan.util.io.UnzipUtils;
import com.vividsolutions.jts.geom.Geometry;

public class ShapefileProcessor implements EquusProcessor
{

    private static final File TEMP_UNZIP_DIR = new File(
        System.getProperty("java.io.tmpdir") + File.separator
                + "atlas_temp_unzip_dir");

    public static Set<BasicFeature> importFeatures(final File zipFile)
        throws EquusException
    {
        // Check if the input file has the zipfile extension 
        if (!zipFile.getName().endsWith(".zip"))
        {
            throw new EquusException(
                    "The file is not a zipfile. It cannot be processed.");
        }

        // Unzip the file
        try
        {
            UnzipUtils.unzip(zipFile, TEMP_UNZIP_DIR);
        }
        catch (IOException error)
        {
            throw new EquusException("The zipfile cannot be unzipped.", error);
        }

        // Validate whether the unzipped folder contains a shapefile and return it
        File shapefile = new File("");
        try
        {
            shapefile = findShapefile(TEMP_UNZIP_DIR);
        }
        catch (IOException error)
        {
            throw new EquusException(
                    "The zipfile does not contain a shapefile. Cannot process its contents.",
                error);
        }

        // Collect the features from the shapefile and put them into an iterator 
        FeatureIterator<SimpleFeature> featureIterator;
        try
        {
            featureIterator = readShapefile(shapefile);
        }
        catch (EquusException e)
        {
            throw new EquusException(e.getMessage(), e);
        }

        // Create a Set filled with the features in the FeatureIterator
        Set<BasicFeature> features = createFeatureSet(featureIterator);

        return features;

    }

    private static File findShapefile(File unzipPath) throws IOException
    {
        File shapefile = new File("");
        // Find first .shp file in the unzip folder
        File[] unzippedFiles = unzipPath.listFiles();
        for (int i = 0; i < unzippedFiles.length; i++)
        {
            if (unzippedFiles[i].getName().endsWith(".shp"))
            {
                shapefile = new File(unzipPath + File.separator
                        + unzippedFiles[i].getName());
                break;
            }
        }
        if (shapefile.toString() == "")
        {
            throw new IOException("No shapefile present in '" + unzipPath
                + "'.");
        }
        return shapefile;
    }

    private static FeatureIterator<SimpleFeature> readShapefile(File shapefile)
        throws EquusException
    {
        // Collects the features from a shapefile and puts them into an iterator
        FeatureCollection<SimpleFeatureType, SimpleFeature> featureCollection;
        try
        {
            Map<String, URL> connectParameters = new HashMap<String, URL>();
            connectParameters.put("url", shapefile.toURI().toURL());
            DataStore dataStore = DataStoreFinder.getDataStore(connectParameters);
            String typeName = dataStore.getTypeNames()[0];
            FeatureSource<SimpleFeatureType, SimpleFeature> featureSource = dataStore.getFeatureSource(typeName);
                featureCollection = featureSource.getFeatures();
        }
        catch (Exception e)
        {
            throw new EquusException(
                    "Features cannot be retrieved from the shapefile.", e);
        }
        return featureCollection.features();
    }

    private static Set<BasicFeature> createFeatureSet(
            FeatureIterator<SimpleFeature> featureIterator)
    {
        SimpleFeature simpleFeature = null;
        Set<BasicFeature> features = new HashSet<BasicFeature>();
        while (featureIterator.hasNext())
        {
            simpleFeature = featureIterator.next();
            BasicFeature feature = new BasicFeature();
            feature.setGeometry((Geometry) simpleFeature.getDefaultGeometry());
            features.add(feature);
        }
        return features;
    }
}

Answer 1

只需像这样使用ShapefileDataStore的构造函数：

// URL url = file.toURI().toURL();
DataStore shapefileStore = new ShapefileDataStore(url)

Answer 2

虽然您的代码看起来正确，但我发现我们代码库中关键行的实现略有不同：

Map<String, Object> map = new HashMap<>();
map.put(ShapefileDataStoreFactory.URLP.key, url);
map.put(ShapefileDataStoreFactory.CREATE_SPATIAL_INDEX.key, Boolean.TRUE);
DataStore shapefileStore = DataStoreFinder.getDataStore(map);

Answer 3

您的代码是正确的，但您的类路径缺少 ShapeFileDataStore。 通过添加例如：gt2-shapefile-2.3.2.jar

来修复您的类路径

或者直接使用

DataStore shapefileStore = new ShapefileDataStore(url)

这具有您立即会看到的优点，即您的代码由于缺少 shapefile 库而无法编译。

有

Iterator availableStores =  DataStoreFinder.getAvailableDataStores();

您可以输出所有可用数据存储的列表。如果为空或没有列出 ShapefileDataStoreFactory，您将知道原因是类路径。