java使用gdal把dxf转为json,并设置坐标系

使用 Java 调用 GDAL 库将 DXF 格式转换为 JSON 格式，可以参考以下步骤：

1. 安装 GDAL 库：可参考 GDAL 官方文档进行安装。

2. 使用 Java 调用 GDAL 库：在 Java 中可以使用 JNA 或 JNI 调用 GDAL 库，这里以 JNA 为例介绍。

3. 代码示例：

import com.sun.jna.Library;
import com.sun.jna.Native;
import com.sun.jna.Pointer;

public interface GdalLibrary extends Library {
    GdalLibrary INSTANCE = Native.load("gdal", GdalLibrary.class);

    Pointer GDALCreate(char[] pszDriverName, int nXSize, int nYSize, int nBands, int eBandType, String[] options);

    void GDALClose(Pointer dataset);

    int OGRRegisterAll();

    Pointer OGRSFDriverRegistrar_getRegistrar();

    void OGRRegisterAll();

    Pointer OGRSFDriverRegistrar_getDriverByName(Pointer registrar, String name);

    Pointer OGR_Dr_CreateDataSource(Pointer driver, String name, String[] options);

    Pointer OGR_DS_CreateLayer(Pointer datasource, String name, Pointer spatialRef, int geometryType, String[] options);

    void OGR_Fld_Create(Pointer layer, Pointer fieldDefn, int approxOK);

    Pointer OGR_FldDefn_New(String name, int type);

    void OGR_Fld_Destroy(Pointer fieldDefn);

    void OGR_L_CreateField(Pointer layer, Pointer fieldDefn, int approxOK);

    void OGR_L_SetSpatialFilter(Pointer layer, Pointer geometry);

    void OGR_L_SetAttributeFilter(Pointer layer, String filter);

    Pointer OGR_G_CreateGeometry(int type);

    void OGR_G_DestroyGeometry(Pointer geometry);

    void OGR_G_AddPoint(Pointer geometry, double x, double y, double z);

    void OGR_G_AddGeometry(Pointer geometry, Pointer geometry2);

    String OGR_G_ExportToJson(Pointer geometry);

    void CPLFree(Pointer pointer);
}

public static void dxf2json(String dxfPath, String jsonPath, String srs) {
    String[] args = new String[] {
            "-f",
            "GeoJSON",
            jsonPath,
            dxfPath
    };
    GdalLibrary.INSTANCE.OGRRegisterAll();
    Pointer hDriver = GdalLibrary.INSTANCE.OGRSFDriverRegistrar_getDriverByName(
            GdalLibrary.INSTANCE.OGRSFDriverRegistrar_getRegistrar(), "DXF");
    Pointer hDataSource = GdalLibrary.INSTANCE.OGR_Dr_CreateDataSource(hDriver, dxfPath, null);
    Pointer hLayer = GdalLibrary.INSTANCE.OGR_DS_CreateLayer(hDataSource, "layer", null, 1, null);
    GdalLibrary.INSTANCE.OGR_L_CreateField(hLayer, GdalLibrary.INSTANCE.OGR_FldDefn_New("Id", 0), 1);

    Pointer hSpatialRef = null;
    if (StringUtils.isNotEmpty(srs)) {
        hSpatialRef = GdalLibrary.INSTANCE.OSRNewSpatialReference(null);
        GdalLibrary.INSTANCE.OSRSetFromUserInput(hSpatialRef, srs);
        GdalLibrary.INSTANCE.OGR_L_SetSpatialFilter(hLayer, hSpatialRef);
    }

    int argc = args.length;
    String[] argv = new String[argc];
    for (int i = 0; i < argc; i++) {
        argv[i] = args[i];
    }
    Pointer hArgv = GdalLibrary.INSTANCE.CPLStringListToargv(argc, argv);
    Pointer hDstDS = GdalLibrary.INSTANCE.GDALCreate("GeoJSON", 0, 0, 0, 0, null);
    GdalLibrary.INSTANCE.GDALVectorTranslate(hDstDS, hArgv, null);
    GdalLibrary.INSTANCE.GDALClose(hDstDS);

    if (hSpatialRef != null) {
        GdalLibrary.INSTANCE.OSRDestroySpatialReference(hSpatialRef);
    }
    GdalLibrary.INSTANCE.OGR_Fld_Destroy(GdalLibrary.INSTANCE.OGR_L_GetLayerDefn(hLayer).getFieldDefn(0));
    GdalLibrary.INSTANCE.OGR_DS_Destroy(hDataSource);
}

其中，dxfPath 为输入的 DXF 文件路径，jsonPath 为输出的 JSON 文件路径，srs 为坐标系信息，可以根据需要自行设置。

这里使用了 GDAL 的 OGR API，具体使用方法可以参考 GDAL 官方文档。