与后台数据库同步
类DBManager也允许应用程序开发者用PointBase 专有UniSync引擎与后台数据库同步移动数据。不同的厂商使用不同的同步引擎，但他们的概念都是相类似的。同步过程按照如下这些步骤进行：
1. 在后台服务器和移动设备上创建相应的数据库和表
2. 在同步服务器上创建一个hub。这个hub包含发布信息。它指定和标识用于同步（发布）的后台表（或部分表）。
3. 使用hub来创建spoke。spoke是在同步服务器上表示移动设备的对象。每个spoke都有一个ID。它能通过在同一个hub里的订阅对象来订阅发布。通过使用一个spokeID，移动设备匹配spoke并对订阅的后台表进行同步。
4. 启动同步服务器。基本上通过com.pointbase.me.sync.Server 类的main()方法来执行。这个服务器类用于PointBase 发布包。还有其他几个方法在不同环境中运行服务器。您可以参考PointBase文档来得到更多的细节和例子。默认情况下，服务器监听端口8124。
5. 使用一个spokeID和在移动设备上的类 spoke stub 来初始化同步过程。
图3 UniSync同步服务器框架图解
例3 中的类ResetServer显示了在UniSync服务器上如何创建hub和spoke：
例3 安装同步服务器
manager=SyncManager.getInstance(caturl,catdriver,catuser,catpassword);
String dsname;
dsname=SyncDataSource.DEFAULT;
String hubname="Hub";
Hub hub=manager.createHub(hubname);
Publication pub;
String pubname;
SpokeConfig spoke;
Subscription sub;
String subname="SubNameCard";
String tablename="NAMECARD";
String[] tables=new String[]{tablename};
// Publish the complete name-card table
pubname="PubNameCard";
pub=hub.newPublication(pubname,dsname,tables);
hub.publish(pub);
// Create two spokes and subscribe to this publication
for(int i=1;i<=2;i++) {
String name="Spoke"+i;
spoke=hub.createSpokeConfig(name);
spoke.savePassword("pass"+i);
sub=spoke.newSubscription(subname,SyncDataSource.DEFAULT,pubname);
spoke.subscribe(sub);
}
// Publish the name-card table without the picture column
pubname="PubNameCardNoPicture";
pub=hub.newPublication(pubname,dsname,tables);
SyncTable table=pub.getSyncTable(tablename);
table.dropSyncColumns(new String[]{"PICTURE"});
hub.publish(pub);
// Create two spokes and subscribe to this publication
for(int i=3;i<=4;i++) {
String name="Spoke"+i;
spoke=hub.createSpokeConfig(name);
spoke.savePassword("pass"+i);
sub=spoke.newSubscription(subname,SyncDataSource.DEFAULT,pubname);
spoke.subscribe(sub);
}
manager.close(); |
下面的DBManager代码片断显示了如何获得spoke stub 和如何在设备上处理同步。代码中的注释解释了应用程序的同步和独立版本的不同：
例4 通过同步服务器访问数据
// Import proprietary classes for sync
import com.pointbase.me.jdbc.*;
class DBManager {
// In addition to JDBC connection variables,
// we also need to define variables for sync
// ... ...
private Spoke spoke;
private String spokename;
private int spoke_id;
private int spoke_range_start,spoke_range_end;
final static int ROWS_PER_SPOKE=1<<16;
private String syncurl;
private String syncpassword;
private DBManager() {
// Get DB connection parameters
// ... ...
// Get sync parameters
syncurl =
properties.getProperty("syncurl", "http://localhost:8124";);
String spokeid =
properties.getProperty("spokeid", "1");
spokename =
properties.getProperty("spoke", "Spoke"+spokeid);
syncpassword =
properties.getProperty("syncpassword", "pass"+spokeid);
url =
properties.getProperty("url",
"jdbc:pointbase:micro:pbdemo"+spokeid);
connect();
}
// The complete connect method using synchronization server
private void connect() {
try {
System.out.println("Connecting to the database...");
Class.forName(driver);
// If the database doesn't exist, create a new database
connection = DriverManager.getConnection(url, user, password);
statement = connection.createStatement();
// Check sync metadata and create tables
loadMeta();
// Create prepared statements
createStatement();
} catch (Exception e) {
e.printStackTrace();
System.exit(1);
}
}
// The complete newID method using the sync server
private int getNewID() {
try {
ResultSet rs = statement.executeQuery(
"SELECT MAX(ID)+1 FROM NameCard WHERE "+
"ID>="+spoke_range_start+" AND ID<"+spoke_range_end);
rs.next();
int id=rs.getInt(1);
if(rs.wasNull()) {
return spoke_range_start;
} else {
return id;
}
} catch (Exception e) {
e.printStackTrace();
}
return 0;
}
// Create table and load metadata from the sync hub
void loadMeta() {
try {
SyncManager manager=SyncManager.getInstance(connection);
spoke=manager.getSpoke(spokename);
if(spoke==null) {
System.out.println(
"Loading MetaData from url "+syncurl+
" for spoke "+spokename+
" using password "+syncpassword);
spoke=manager.createSpoke(spokename);
spoke.savePassword(syncpassword);
spoke.saveHubURL(syncurl);
spoke.loadConfig();
spoke.getSnapshot();
}
spoke_id = spoke.getSpokeId();
System.out.println("SpokeID is "+spoke_id);
spoke_range_start = ROWS_PER_SPOKE * spoke_id;
spoke_range_end = spoke_range_start + ROWS_PER_SPOKE - 1;
} catch (SyncException e) {
e.printStackTrace();
}
}
// Synchronize spoke databases (mobile databases) with the hub
// and backend databases
void sync() {
try {
spoke.sync();
} catch (SyncException e) {
e.printStackTrace();
}
}
// Other data access methods are the same as the non-synced version.
} |
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