Question

Hey StackOverflow社区，我目前正在尝试编写一个小工具，它读取shapefile的几何图形（Multipolygons / Polygons），并将这些工具的WKT表示写入文本文件。为了做到这一点，我正在使用GeoTools并且我设法让它运行正常，因为我正在转换大约5000000个多边形/多边形的文件，这需要很长时间才能完成。

所以我的问题是：

是否可以加载文件加载/写入？当我使用SimpleFeatureIterator时，我没有找到如何实现多线程。

有没有办法这样做？或者有人知道，如何在不使用迭代器的情况下获取shapefile几何图形？

这是我的代码：

此方法只是声明文件选择器并为每个选定文件启动线程。

protected static void printGeometriesToFile() {
    JFileChooser chooser = new JFileChooser();
    FileNameExtensionFilter filter = new FileNameExtensionFilter(
            "shape-files", "shp");
    chooser.setFileFilter(filter);
    chooser.setDialogTitle("Choose the file to be converted.");
    chooser.setMultiSelectionEnabled(true);
    File[] files = null;

    int returnVal = chooser.showOpenDialog(null);
    if (returnVal == JFileChooser.APPROVE_OPTION) {
        files = chooser.getSelectedFiles();
    }

    for (int i = 0; i < files.length; i++) {
        MultiThreadWriter writer = new MultiThreadWriter(files[i]);
        writer.start();
    }
}

多线程类：

class MultiThreadWriter extends Thread {
    private File threadFile;

    MultiThreadWriter(File file) {
        threadFile = file;
        System.out.println("Starting Thread for " + file.getName());
    }

    public void run() {
        try {
            File outputFolder = new File(threadFile.getAbsolutePath() + ".txt");
            FileOutputStream fos = new FileOutputStream(outputFolder);
            System.out.println("Now writing data to file: " + outputFolder.getName());

            FileDataStore store = FileDataStoreFinder.getDataStore(threadFile);
            SimpleFeatureSource featureSource = store.getFeatureSource();

            SimpleFeatureCollection featureCollection = featureSource.getFeatures();
            SimpleFeatureIterator featureIterator = featureCollection.features();

            int pos = 0;

            while (featureIterator.hasNext()) {
                fos.write((geometryToByteArray((Polygonal) featureIterator.next().getAttribute("the_geom"))));

                pos++;
                System.out.println("The file " + threadFile.getName() + "'s current positon is: " + pos);
            }

            fos.close();

            System.out.println("Finished writing.");

        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

这只是一个帮助函数，它将多面体转换为多边形，并使用＆＃34; |＆＃34;返回其WKT表示。作为一个分离者。

private byte[] geometryToByteArray(Polygonal polygonal) {

    List<Polygon> polygonList;

    String polygonString = "";

    if (polygonal instanceof MultiPolygon) {
        polygonList = GeometrieUtils.convertMultiPolygonToPolygonList((MultiPolygon) polygonal);
     //The method above just converts a MultiPolygon into a list of Polygons
    } else {
        polygonList = new ArrayList<>(1);
        polygonList.add((Polygon) polygonal);
    }

    for (int i = 0; i < polygonList.size(); i++) {
        polygonString = polygonString + polygonList.get(i).toString() + "|";
    }

    return polygonString.getBytes();
}

}

我知道我的代码不是很好或不好。我刚刚开始学习Java，希望它能很快好起来。

真诚

ihavenoclue：）

Answer 1

您不需要为每个文件创建新线程，因为创建新线程是一项昂贵的操作。相反，您可以让MultiThreadWriter实现Runnable并使用ThreadPoolExecuter管理所有主题。

MultiThreadWriter

public class MultiThreadWriter implements Runnable {
    @Override
    public void run() {
        //
    }
}

创建线程池与运行时处理器匹配。

ExecutorService service = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors());

for (int i = 0; i < files.length; i++) {
    MultiThreadWriter writer = new MultiThreadWriter(files[i]);
    service.submit(writer);
}

您可以使用BufferedWriter代替OutputStream，当您重复编写小件时，more efficient。

File outputFolder = new File(threadFile.getAbsolutePath() + ".txt");
FileOutputStream fos = new FileOutputStream(outputFolder);
BufferedWriter writer = new BufferedWriter(fos);

Answer 2

我更愿意将文件内容作为对象列表读取，然后将列表拆分为子列表，然后为每个列表创建一个线程，例如：

int nbrThreads = 10;

ThreadPoolExecutor executor = (ThreadPoolExecutor) Executors.newFixedThreadPool(nbrThreads);

int count = myObjectsList != null ? myObjectsList.size() / nbrThreads : 0;

List<List<MyObject>> resultlists = choppeList(myObjectsList, count > 0 ? count : 1);

try
{
    for (List<MyObject> list : resultlists)
    {
        // TODO : create your thread and passe the list of objects   
    }

    executor.shutdown();

    executor.awaitTermination(30, TimeUnit.MINUTESS); // chose time of termination
}
catch (Exception e)
{
    LOG.error("Problem launching threads", e);
}

choppeList方法可以是这样的：

public <T> List<List<T>> choppeList(final List<T> list, final int L)
{
    final List<List<T>> parts = new ArrayList<List<T>>();
    final int N = list.size();
    for (int i = 0; i < N; i += L)
    {
        parts.add(new ArrayList<T>(list.subList(i, Math.min(N, i + L))));
    }
    return parts;
}

使用GeoTools加载多线程几何

2 个答案: