基于GeoTools的WMS设计与实现

GeoTools是一个Java软件包地理实现。

WMS是一种服务设计理念。

 由上图可见，后端一共有三个函数GetCapabilities、GetMap和GetFeatureInfo，根据接收到的客户端的参数来分别进行调用。并将结果返回给客户端，WMS一般是返回图像格式的文件。

基于GeoTools的WMS的设计与实现，可以直接看GeoServer，它就是基于GeoTools的WMS实现。而且还包含了Jetty服务器，可以直接使用。当然也可以使用War包版本，放在Tomcat服务器下面。

第一步：拦截请求参数

public void doService(HttpServletRequest request,
        HttpServletResponse response) throws IOException {
    Map map = request.getParameterMap();
    Map param = new HashMap();
    for (String k : map.keySet()) {
        String s1 = "";
        if (param.containsKey(k.toUpperCase())) {
            s1 = param.get(k.toUpperCase()) + ",";
        }
        String[] s2 = (String[]) map.get(k);
        for (int i = 0; i < s2.length; i++) {
            s1 += s2[i] + (i == 0 ? "" : ",");
        }
        param.put(k.toUpperCase(), s1);
    }
    if (!param.containsKey("REQUEST")) {
        WMSException.exception(response);
    } else {
        String wmsRequest = param.get("REQUEST");
        if (wmsRequest.equals("GetCapabilities")) {
            GetCapabilitiesRequest gcr = new GetCapabilitiesRequest(param);
            doGetCapabilities(gcr, response);
        } else if (wmsRequest.equals("GetMap")) {
            GetMapRequest gmr = new GetMapRequest(param);
            doGetMap(gmr, response);
        } else if (wmsRequest.equals("GetFeatureInfo")) {
            GetFeatureInfoRequest gfr = new GetFeatureInfoRequest(param);
            doGetFeatureInfo(gfr, response);
        } else {
            WMSException.exception(response);
        }
    }
}

第二步：

private static void addShapeLayer(String name) throws Exception {
    File file = new File("C:data" + name + ".shp");
    File sldFile = new File("C:data" + name + ".sld");
    FileDataStore store = FileDataStoreFinder.getDataStore(file);
    ((ShapefileDataStore) store).setStringCharset(Charset.forName("GB2312"));
    FeatureSource featureSource = store
            .getFeatureSource();
    Configuration config = new SLDConfiguration();
    Parser parser = new Parser(config);
    InputStream sld = new FileInputStream(sldFile);
    StyledLayerDescriptor styleSLD = (StyledLayerDescriptor) parser.parse(sld);
    Style style = SLD.defaultStyle(styleSLD);
    map.addLayer(featureSource, style);
}

第三步：

private void doGetMap(GetMapRequest gmr, HttpServletResponse response)
        throws IOException {
    double x1, y1, x2, y2;
    int width, height;
    try {
        x1 = Double.parseDouble(gmr.getBBOX()[0]);
        y1 = Double.parseDouble(gmr.getBBOX()[1]);
        x2 = Double.parseDouble(gmr.getBBOX()[2]);
        y2 = Double.parseDouble(gmr.getBBOX()[3]);
        width = Integer.parseInt(gmr.getWidth());
        height = Integer.parseInt(gmr.getHeight());
    } catch (Exception e) {
        WMSException.exception(response);
        return;
    }
    // 设置输出范围
    ReferencedEnvelope mapArea = new ReferencedEnvelope(x1, x2, y1, y2, crs);
    // 初始化渲染器
    StreamingRenderer sr = new StreamingRenderer();
    sr.setContext(map);
    // 初始化输出图像
    BufferedImage bi = new BufferedImage(width, height,
            BufferedImage.TYPE_INT_ARGB);
    Graphics g = bi.getGraphics();
    ((Graphics2D) g).setRenderingHint(RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON);
    ((Graphics2D) g).setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING,
            RenderingHints.VALUE_TEXT_ANTIALIAS_ON);
    Rectangle rect = new Rectangle(0, 0, width, height);
    // 绘制地图
    sr.paint((Graphics2D) g, rect, mapArea);
    // 编码图像
    PNGEncodeParam encodeParam = PNGEncodeParam.getDefaultEncodeParam(bi);
    if (encodeParam instanceof PNGEncodeParam.Palette) {
        PNGEncodeParam.Palette p = (PNGEncodeParam.Palette) encodeParam;
        byte[] b = new byte[] { -127 };
        p.setPaletteTransparency(b);
    }
    //将图像数据输出到Servlet相应中
    response.setContentType("image/png");
    ServletOutputStream out = response.getOutputStream();
    com.sun.media.jai.codec.ImageEncoder encoder = ImageCodec
            .createImageEncoder("PNG", out, encodeParam);
    encoder.encode(bi.getData(), bi.getColorModel());
    bi.flush();
}

 第四步：

private void doGetFeatureInfo(GetFeatureInfoRequest gfr,
        HttpServletResponse response) throws IOException {
    double x1, y1, x2, y2;
    int width, height, i, j;
    try {
        x1 = Double.parseDouble(gfr.getBBOX()[0]);
        y1 = Double.parseDouble(gfr.getBBOX()[1]);
        x2 = Double.parseDouble(gfr.getBBOX()[2]);
        y2 = Double.parseDouble(gfr.getBBOX()[3]);
        width = Integer.parseInt(gfr.getWidth());
        height = Integer.parseInt(gfr.getHeight());
        i = Integer.parseInt(gfr.getI());
        j = Integer.parseInt(gfr.getJ());
    } catch (Exception e) {
        WMSException.exception(response);
        return;
    }
    // 计算点选范围的地图坐标
    double cx1, cy1, cx2, cy2;
    cx1 = x1 * (width - i + 0.5 + GET_FEATURE_INFO_BUFFUR) / width + x2
            * (i - 0.5 - GET_FEATURE_INFO_BUFFUR) / width;
    cx2 = x1 * (width - i + 0.5 - GET_FEATURE_INFO_BUFFUR) / width + x2
            * (i - 0.5 + GET_FEATURE_INFO_BUFFUR) / width;
    cy1 = y1 * (j - 0.5 + GET_FEATURE_INFO_BUFFUR) / height + y2
            * (height - j + 0.5 - GET_FEATURE_INFO_BUFFUR) / height;
    cy2 = y1 * (j - 0.5 - GET_FEATURE_INFO_BUFFUR) / height + y2
            * (height - j + 0.5 + GET_FEATURE_INFO_BUFFUR) / height;
    ReferencedEnvelope clickArea = new ReferencedEnvelope(cx1, cx2, cy1, cy2, crs);
    MapLayer[] maplayers = map.getLayers();
    FilterFactory2 ff = CommonFactoryFinder.getFilterFactory2(null);
    response.setContentType("text/html");
    response.setCharacterEncoding("GBK");
    PrintWriter out = response.getWriter();
    out.println("location: " + ((cx1 + cx2) / 2.0) + ", "
            + ((cy1 + cy2) / 2.0) + "<br/>");
    // 分别在每个图层中查找点选范围内的对象
    for (int k = 0; k < maplayers.length; k++) {
        FeatureSource fs =
            (FeatureSource) maplayers[k].getFeatureSource();
        String geometryPropertyName = fs.getSchema().getGeometryDescriptor().getLocalName();
        Filter filter = ff.bbox(ff.property(geometryPropertyName), clickArea);
        FeatureCollection fc = fs.getFeatures(filter);
        SimpleFeatureType schema = fc.getSchema();
        FeatureIterator fi = fc.features();
        if (fi.hasNext()) {
            out.println("Selected feature(s) in layer ["+schema.getTypeName()+"]:<br/>");
            while (fi.hasNext()) {
                SimpleFeature f = fi.next();
                out.println("id:" + f.getID() + "<br/>");
                for (AttributeDescriptor type : schema
                        .getAttributeDescriptors()) {
                    String name = type.getLocalName();
                    if (!name.equals(geometryPropertyName))
                        out.println(name + ":"
                                + f.getProperty(name).getValue().toString()
                                + "<br/>");
                }
                out.println("<br/>");
            }
        }
    }
    out.flush();
    out.close();
}