Reading an ESRI shapefile from a zip-file during Runtime in Java - DataStoreFinder.getDataStore(connectParameters) returns null

问题

We are building a service for uploading zip-files containing an ESRI-shapefile. The service should be able to read the shapefile and do stuff with its content. So I've built a class that unzips the zip-file to temporary folder (subfolder of System.getProperty("java.io.tmpdir")).

Another class calls the unzip method from the Unzip-class and it then tries to read the unpacked shapefile using Geotools. It uses the Geotools DataStoreFinder.getDataStore(Map params) method to create a datastore from the unzipped shapefile. Here the problem occurs: the getDataStore-method returns null. I tested the URL, it looks allright. The file from which the URL derives exists, is a file and can be read by the application (tested using shapefile.exists(), shapefile.isFile(), shapefile.canRead()). So , what could be wrong? Why do I get null returned?

Here's the (relevant) code:

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;
    }
}

回答1:

Though your code seems correct, I have found a slightly different implementation of the crucial lines in our codebase:

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);

回答2:

Just use the constructor of ShapefileDataStore like this:

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

回答3:

Your code is correct, but your classpath is missing the ShapeFileDataStore. Either fix your class path by adding the e.g: gt2-shapefile-2.3.2.jar

Or directly use

DataStore shapefileStore = new ShapefileDataStore(url)

This has the advanatage that you immedeatly will see, that your code cannot compile, due missing shapefile library.

With

Iterator availableStores =  DataStoreFinder.getAvailableDataStores();

you can output a list of all available data stores. If empty or if there is no ShapefileDataStoreFactory listed, you will know the cause is the classpath.

来源：https://stackoverflow.com/questions/14242111/reading-an-esri-shapefile-from-a-zip-file-during-runtime-in-java-datastorefind