概述：
经过一个春节的休整，今天最终開始了！
任何时候。都不要忘记学习。学习是一辈子的事情！今天，我来说说怎样实现天地图的离线以及Openlayers载入离线数据实现天地图数据的展示。
实现：
1、获取天地图的数据
能够通过网络上下载各大地图的工具将天地图的数据下载下来。并制作成mbtiles文件。制作过程在此就不详述，将已经制作好的一个文件上传到了百度网盘。须要的童鞋能够下载哦~~~~
下载链接：http://pan.baidu.com/s/1dEmNtnF password：xqd8
2、读取mbtiles并返回到页面
mbtiles事实上就是一个sqllite数据库， 其具体可移步至http://www.cnblogs.com/i-gps/p/3919475.html查看具体。
在此方案中，我用了一个servlet。具体的实现代码例如以下：
package com.lzugis.web;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Created by Administrator on 2016/2/27.
*/
@WebServlet(description = "tian ditu tile", urlPatterns = {"/tdttile"})
public class TiandituTile extends HttpServlet {
private String tilepath = "D:/data/tdt/";
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String tile_column = request.getParameter("X");
String tile_row = request.getParameter("Y");
String zoom_level = request.getParameter("L");
String layer = request.getParameter("T");
// TODO Auto-generated method stub
try {
Class.forName("org.sqlite.JDBC");
}
catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
// e.printStackTrace();
System.out.println("数据库驱动未找到!");
}
// 得到连接 会在你所填写的文件夹建一个你命名的文件数据库
Connection conn;
try {
String conurl = "jdbc:sqlite:"+tilepath+layer+".mbtiles";
conn = DriverManager.getConnection(conurl,null,null);
// 设置自己主动提交为false
conn.setAutoCommit(false);
Statement stmt = conn.createStatement();
//推断表是否存在
ResultSet rsTables = conn.getMetaData().getTables(null, null, "tiles", null);
if(!rsTables.next()){
System.out.println("表不存在");
}
// 得到结果集
String sql = "SELECT * FROM tiles WHERE zoom_level = "+zoom_level+
" AND tile_column = "+tile_column+
" AND tile_row = "+tile_row;
ResultSet rs = stmt.executeQuery(sql);
if(rs.next()) {
byte[] imgByte = (byte[]) rs.getObject("tile_data");
InputStream is = new ByteArrayInputStream(imgByte);
OutputStream os = response.getOutputStream();
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();
}
}
else{
System.out.println(sql);
System.out.println("未找到图片！"); } rs.close(); conn.close(); } catch (SQLException e) { e.printStackTrace(); System.out.println("SQL异常!"); } } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request,response); } }
当中，请求地址为：http://localhost:8081/lzugis/tdttile?T=vec_c&L=5&X=25&Y=3。请求的结果例如以下所看到的：
3、openlayers调用
从网上拔了下openlayers载入天地图的代码。并稍作改动。扩展了一个openlayers图层TiandituLayer。其代码例如以下：
OpenLayers.Layer.TiandituLayer = OpenLayers.Class(OpenLayers.Layer.Grid,{
mapType : null,
mirrorUrls : null,
topLevel : null,
bottomLevel : null,
//用于标识是本地天地图切片库还是訪问在线天地图
isOnline:true,
topLevelIndex : 0,
bottomLevelIndex : 20,
topTileFromX : -180,
topTileFromY : 90,
topTileToX : 180,
topTileToY : -270,
isBaseLayer : true,
initialize : function(name, url, options) {
options.topLevel = options.topLevel ? options.topLevel
: this.topLevelIndex;
options.bottomLevel = options.bottomLevel ?options.bottomLevel : this.bottomLevelIndex; options.maxResolution = this .getResolutionForLevel(options.topLevel); options.minResolution = this .getResolutionForLevel(options.bottomLevel); var newArguments = [ name, url, {}, options ]; OpenLayers.Layer.Grid.prototype.initialize.apply(this, newArguments); }, clone : function(obj) { if (obj == null) { obj = new OpenLayers.Layer.TiandituLayer(this.name, this.url, this.options); } obj = OpenLayers.Layer.Grid.prototype.clone .apply(this, [ obj ]); return obj; }, getURL : function(bounds) { var level = this.getLevelForResolution(this.map.getResolution()); var coef = 360 / Math.pow(2, level); var x_num = this.topTileFromX < this.topTileToX ?
Math .round((bounds.left - this.topTileFromX) / coef) : Math .round((this.topTileFromX - bounds.right) / coef); var y_num = this.topTileFromY < this.topTileToY ?
Math .round((bounds.bottom - this.topTileFromY) / coef) : Math.round((this.topTileFromY - bounds.top) / coef); var type = this.mapType; var url = this.url; if (this.mirrorUrls != null) { url = this.selectUrl(x_num, this.mirrorUrls); } return this.getFullRequestString({ T : type, X : x_num, Y : y_num, L : level }, url); }, getFullRequestString: function(params, url){ url = url+'?T='+params.T+'&L='+params.L+'&X='+params.X+'&Y='+params.Y; return url; }, selectUrl : function(a, b) { return b[a % b.length] }, getLevelForResolution : function(res) { var ratio = this.getMaxResolution() / res; if (ratio < 1) return 0; for ( var level = 0; ratio / 2 >= 1;) { level++; ratio /= 2; } return level; }, getResolutionForLevel : function(level) { return 360 / 256 / Math.pow(2, level); }, getMaxResolution : function() { return this.getResolutionForLevel(this.topLevelIndex) }, getMinResolution : function() { return this.getResolutionForLevel(this.bottomLevelIndex) }, CLASS_NAME : "OpenLayers.Layer.TiandituLayer" });
在代码中新建一个TiandituLayer。并加入到map中就可以实现，代码例如以下：
OpenLayers MapQuest Demo
1、代码中vec_c为天地图矢量层。cva_c为天地图标注层，与天地图的名称相一致；
2、vec_c为离线的地图，cva_c为在线的，通过參数isOnline区分其为离线还是在线。
完毕后效果：
