概述
本文實現的是結合Openlayers4和java servlet實現公網資源切片的本地緩存。
優點
相比較其他下載利器，本實例具有以下優點： 1. 實現簡單，操作簡單； 2. 不會出現IP被封； 3. 結合web，看到哪下到哪，主動保存未緩存的切片； 4. 可通過修改URL和代碼緩存多種地圖切片。
缺點
鑑於web的實現，該切片緩存的方式具有以下缺點： 1. 被動式緩存，需要用戶瀏覽需要下載的區域； 2. 無法批量緩存。 3. 主要是針對開發人員的，非開發人員使用有困難；
實現效果
實現思路
實現代碼
頁面代碼
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>切片下載</title>
<link rel="stylesheet" href="https://openlayers.org/en/v4.1.1/css/ol.css" type="text/css">
<style type="text/css">
body, #map {
border: 0px;
margin: 0px;
padding: 0px;
width: 100%;
height: 100%;
font-size: 13px;
overflow: hidden;
}
</style>
<script src="https://openlayers.org/en/v4.1.1/build/ol.js"></script>
<script type="text/javascript" src="plugin/jquery/jquery-3.1.1.min.js"></script>
<script type="text/javascript">
var map;
function init(){
var cva_w = getGeoheyLayer("blue");
var province = new ol.layer.Image({
source: new ol.source.ImageWMS({
ratio: 1,
url: 'http://localhost:6080/geoserver/bj_grid/wms',
params: {
'FORMAT': 'image/png',
'VERSION': '1.1.1',
STYLES: '',
LAYERS: 'bj_grid:bou2_4p',
}
})
});
map = new ol.Map({
controls: ol.control.defaults({
attribution: false
}),
target: 'map',
layers: [cva_w, province],
view: new ol.View({
center: ol.proj.transform([104.214, 35.847], 'EPSG:4326', 'EPSG:3857'),
zoom: 4
})
});
}
function getGeoheyLayer(style){
var url = "http://localhost:8081/lzugis-web/tile?layer="+style+"&z={z}&x={x}&y={y}";
var layer = new ol.layer.Tile({
source: new ol.source.XYZ({
url:url
})
});
return layer;
}
</script>
</head>
<body onLoad="init()">
<div id="map">
</div>
</body>
</html>servlet代碼
package com.lzugis.web.servlet;
import com.lzugis.web.helper.CommonConfig;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.image.BufferedImage;
import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;
/**
* Created by admin on 2017/9/10.
*/
@WebServlet(description = "wms services", urlPatterns = {"/tile"})
public class TileServiceServlet extends HttpServlet {
private String url = "https://s4.geohey.com/s/mapping/";
private String tilepath = "d:/tile/geohey/";
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doGet(request, response);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String x = request.getParameter("x"),
y = request.getParameter("y"),
z = request.getParameter("z"),
layer = request.getParameter("layer");
StringBuffer tileUrl = new StringBuffer();
tileUrl.append(url);
tileUrl.append(layer+"/all?");
tileUrl.append("z="+z+"&x="+x+"&y="+y);
tileUrl.append("&retina=&ak=MGUxMmI2ZTk4YTVhNDEzYmJhZDJkNDM3ZWI5ZDAwOGE");
String tilefile = tilepath+layer+"/"+z+"/"+x+"_"+y+".png";
File tile = new File(tilefile);
byte[] tileByte = null;
/**
* 如果文件存在，則直接讀取文件
* 如果文件不存在，在先保存
*/
if(tile.exists()){
tileByte = getFileBytes(tilefile);
}
else{
tileByte = getUrlBytes(tileUrl.toString());
saveTileFile(tileByte, tilefile);
}
OutputStream os = response.getOutputStream();
InputStream is = new ByteArrayInputStream(tileByte);
try {
int count = 0;
byte[] buffer = new byte[1024 * 1024];
while ((count = is.read(buffer)) != -1) {
os.write(buffer, 0, count);
}
os.flush();
}
catch (IOException e) {
e.printStackTrace();
}
finally {
os.close();
is.close();
}
}
private void saveTileFile(byte[] tileByte, String tilefile){
try {
BufferedImage bi = null;
bi = ImageIO.read(new ByteArrayInputStream(tileByte));
//判斷文件夾是否存在，否則創建
File filetile = new File(tilefile);
if (!filetile.getParentFile().exists()) {
filetile.getParentFile().mkdirs();
}
ImageIO.write(bi, "png", filetile);
}catch (Exception e){
e.printStackTrace();
}
}
private byte[] getFileBytes(String tilefile){
byte[] buffer = null;
try {
File file = new File(tilefile);
FileInputStream fis = new FileInputStream(file);
ByteArrayOutputStream bos = new ByteArrayOutputStream(1000);
byte[] b = new byte[1000];
int n;
while ((n = fis.read(b)) != -1) {
bos.write(b, 0, n);
}
fis.close();
bos.close();
buffer = bos.toByteArray();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return buffer;
}
private byte[] getUrlBytes(String tilurl){
try {
//new一個URL對象
URL url = new URL(tilurl);
//打開鏈接
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
//設置請求方式爲"GET"
conn.setRequestMethod("GET");
//超時響應時間爲5秒
conn.setConnectTimeout(5 * 1000);
//通過輸入流獲取圖片數據
InputStream inStream = conn.getInputStream();
//得到圖片的二進制數據，以二進制封裝得到數據，具有通用性
ByteArrayOutputStream outStream = new ByteArrayOutputStream();
//創建一個Buffer字符串
byte[] buffer = new byte[1024];
//每次讀取的字符串長度，如果爲-1，代表全部讀取完畢
int len = 0;
//使用一個輸入流從buffer裏把數據讀取出來
while ((len = inStream.read(buffer)) != -1) {
//用輸出流往buffer裏寫入數據，中間參數代表從哪個位置開始讀，len代表讀取的長度
outStream.write(buffer, 0, len);
}
//關閉輸入流
inStream.close();
//把outStream裏的數據寫入內存
return outStream.toByteArray();
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
}