高可靠性移动应用程序-移动数据库和J2ME工具(2)
翻译作者：jungleguo 2003-11-15
原文： http://www.javaworld.com/javaworld/jw-06-2003/jw-0606-wireless-p2.html
一个应用程序例子
现在通过一个简单的例子，我们检测一下移动数据库应用程序的典型用法和关键组件。
移动联系管理器
这是一个由PointBase提供的移动联系管理器的例子。联系管理器 contact manager包括在PointBase 4.x中。为了读者方便，我已经把源代码打包成zip文件放在Resource中。如果你想编译和运行例子，你必须先从PointBase处下载适当的jar文件。
这个应用程序本身比较简单。它主要沿用了高级地址本应用程序的通用特性。例如，它允许用户存储联系人名字，地址和电话号码；提供自觉浏览和搜索接口；和后台数据库服务器同步。图1和图2分别显示了该应用程序在标准模式和同步模式下的操作。这些屏幕快照来自一个由Insignia’s Jeode PersonalJava VM驱动的Pocket PC 和一个由J2SE驱动的Mac OS X 膝上型电脑。相同字节代码的应用程序没有经过修改运行在许多平台上，证明了Java的威力。
图1 在袖珍PC Jeode PersonalJava上的标准联系管理器
图2 在Mac OS X上的两个同步的联系管理器spoke
客户端应用程序UI（用户界面）是用AWT写的。这是被PersonalJava或J2ME/FP/PP设备所支持的唯一标准UI库。除了这些UI驱动，我们还有另一个代码层，它提供访问一般的设备上JDBC数据库。这个数据库访问层也提供了与后台服务器同步移动数据的逻辑，它是通过PointBase专有UniSync同步服务器来实现的。现在我们来看看数据访问层的代码，它包括在一个单独的类：DBManager.
设备上的数据访问
类DBManager是一个单独的类，它提供从应用程序单点访问数据。这个单独模式避免了嵌入式数据库的线程复杂性。下面的代码片断显示了DBManager的构造器和初始化的代码。它连接数据库，定义表，将测试数据导入表中，创建为以后时候的SQL状态模版（PreparedStatement）。正如我们所看到的，这里用到的都是标准JDBC。对于企业Java 开发者下面的代码应该很容易明白：
例1 连接移动数据库和初始化访问对象
class DBManager {
// DBManager is a singleton class.
private static DBManager instance;
private java/lang/String.java.html" target="_blank">String driver;
private java/lang/String.java.html" target="_blank">String url;
private java/lang/String.java.html" target="_blank">String user;
private java/lang/String.java.html" target="_blank">String password;
private boolean delay;
private Connection connection;
private Statement statement;
private PreparedStatement insert;
private PreparedStatement find;
private PreparedStatement delete;
private PreparedStatement update;
private PreparedStatement all;
static DBManager getInstance() {
if (instance == null) {
instance = new DBManager();
}
return instance;
}
private DBManager() {
// Get parameters from runtime properties.
// This allows us to switch to different JDBC databases
// without changing the application code.
Properties properties = ContactManager.getProperties();
driver =
properties.getProperty("driver", "com.pointbase.me.jdbc.jdbcDriver");
url =
properties.getProperty("url", "jdbc:pointbase:micro:pbdemo");
user =
properties.getProperty("user", "PBPUBLIC");
password =
properties.getProperty("password", "PBPUBLIC");
delay =
properties.getProperty("delayread","true").equals("true");
connect();
}
private void connect() {
try {
// Load the driver class.
java/lang/Class.java.html" target="_blank">Class.forName(driver);
// If the database doesn’t exist, create a new database.
connection = DriverManager.getConnection(url, user, password);
// Create template statement objects.
statement = connection.createStatement();
createStatement();
// If the database is newly created, load the schema.
boolean newdb=initDatabase();
// Load sample data for the new tables.
if(newdb) {
SampleDataCreator.insert(connection);
}
} catch (java/lang/Exception.java.html" target="_blank">Exception e) {
e.printStackTrace();
java/lang/System.java.html" target="_blank">System.exit(1);
}
}
void disconnect() {
try {
connection.commit();
statement.close();
insert.close();
find.close();
delete.close();
update.close();
all.close();
connection.close();
java/lang/System.java.html" target="_blank">System.exit(0);
} catch (java/lang/Exception.java.html" target="_blank">Exception e) {
e.printStackTrace();
java/lang/System.java.html" target="_blank">System.exit(1);
}
}
// Create the table and load the schema.
private boolean initDatabase() {
try {
java/lang/String.java.html" target="_blank">String sql = "CREATE TABLE NameCard (ID INT PRIMARY KEY, "+
"Name VARCHAR(254), Company VARCHAR(254), Title VARCHAR(254), "+
"Address1 VARCHAR(254), Address2 VARCHAR(254), "+
"Phone VARCHAR(254), Email VARCHAR(254), "+
"Picture Binary(1000000))";
// If the table already exists, this will throw an exception.
statement.executeUpdate(sql);
// This means the database already exists.
return true;
} catch (SQLException e) {
// Ignore the error - the table already exists, which is good
// so we don’t need to add demo data later on.
return false;
}
}
// Create statement templates.
private void createStatement() {
try {
insert = connection.prepareStatement(
"INSERT INTO NameCard (ID, Name, Company, Title, Address1, "+
"Address2, Phone, Email, Picture) "+
"VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)");
find = connection.prepareStatement(
"SELECT * FROM NameCard WHERE (Name LIKE ?) "+
"AND (Company LIKE ?) AND (Title LIKE ?) "+
"AND ((Address1 LIKE ?) OR (Address2 LIKE ?)) "+
"AND (Phone LIKE ?) AND (Email LIKE ?)");
delete = connection.prepareStatement(
"DELETE FROM NameCard WHERE ID = ?");
update = connection.prepareStatement(
"UPDATE NameCard SET ID=?, Name=?, Company=?, Title=?, "+
"Address1=?, Address2=?, Phone=?, Email=?, Picture=? "+
"WHERE ID = ?");
all = connection.prepareStatement(
"SELECT ID, Name, Company, Title, Address1, Address2, "+
"Phone, Email FROM NameCard");
} catch (SQLException e) {
e.printStackTrace();
}
}
// Other methods.
}
在DBManager中的其他方法通过简单JDBC API调用进行访问数据库。如下的代码片断展示了搜索和操纵名称卡片记录的方法。这些方法使用了我们之前定义的SQL模版。
例2 数据访问方法
Vector findNameCardsByKeyword(java/lang/String.java.html" target="_blank">String name, java/lang/String.java.html" target="_blank">String company,
java/lang/String.java.html" target="_blank">String title, java/lang/String.java.html" target="_blank">String address1, java/lang/String.java.html" target="_blank">String address2,
java/lang/String.java.html" target="_blank">String phone, java/lang/String.java.html" target="_blank">String email) {
Vector NameCards = new Vector();
java/lang/String.java.html" target="_blank">String[] keywords = {name, company, title, address1, address2,
phone, email};
try {
for (int i = 0; i < keywords.length; i++) {
java/lang/String.java.html" target="_blank">String criteria = (keywords[i].equals("")) ? "%" :
"%" + keywords[i] + "%";
find.setString(i + 1, criteria);
}
ResultSet resultSet = find.executeQuery();
while (resultSet.next()) {
NameCard nameCard = new NameCard(resultSet.getInt(1),
resultSet.getString(2), resultSet.getString(3),
resultSet.getString(4), resultSet.getString(5),
resultSet.getString(6),
resultSet.getString(7), resultSet.getString(8));
if (!delay)
loadPicture(nameCard);
NameCards.addElement(nameCard);
}
} catch (SQLException e) {
e.printStackTrace();
}
return NameCards;
}
void addNameCard(NameCard nameCard) {
nameCard.setID(getNewID());
try {
insert.setInt(1, nameCard.getID());
insert.setString(2, nameCard.getName());
insert.setString(3, nameCard.getCompany());
insert.setString(4, nameCard.getTitle());
insert.setString(5, nameCard.getAddress1());
insert.setString(6, nameCard.getAddress2());
insert.setString(7, nameCard.getPhone());
insert.setString(8, nameCard.getEmail());
insert.setBytes(9, nameCard.getPicture().getBytes());
insert.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
}
}
void updateNameCard(NameCard nameCard) {
try {
update.setInt(1, nameCard.getID());
update.setString(2, nameCard.getName());
update.setString(3, nameCard.getCompany());
update.setString(4, nameCard.getTitle());
update.setString(5, nameCard.getAddress1());
update.setString(6, nameCard.getAddress2());
update.setString(7, nameCard.getPhone());
update.setString(8, nameCard.getEmail());
update.setBytes(9, nameCard.getPicture().getBytes());
update.setInt(10, nameCard.getID());
update.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
}
}
void deleteNameCard(NameCard nameCard) {
try {
delete.setInt(1, nameCard.getID());
delete.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
}
}
void loadPicture(NameCard nameCard) {
try {
ResultSet resultSet =
statement.executeQuery(
"SELECT Picture FROM NameCard WHERE ID = " +
nameCard.getID());
resultSet.next();
Picture picture = new Picture();
picture.setBytes(resultSet.getBytes(1));
nameCard.setPicture(picture);
} catch (SQLException e) {
e.printStackTrace();
}
}
private int getNewID() {
try {
ResultSet resultSet = statement.executeQuery(
"SELECT MAX(ID)+1 FROM NameCard");
if (resultSet.next()) {
return resultSet.getInt(1);
} else {
return 0;
}
} catch (java/lang/Exception.java.html" target="_blank">Exception e) {
e.printStackTrace();
}
return 0;
}
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);
java/lang/String.java.html" target="_blank">String dsname;
dsname=SyncDataSource.DEFAULT;
java/lang/String.java.html" target="_blank">String hubname="Hub";
Hub hub=manager.createHub(hubname);
Publication pub;
java/lang/String.java.html" target="_blank">String pubname;
SpokeConfig spoke;
Subscription sub;
java/lang/String.java.html" target="_blank">String subname="SubNameCard";
java/lang/String.java.html" target="_blank">String tablename="NAMECARD";
java/lang/String.java.html" target="_blank">String[] tables=new java/lang/String.java.html" target="_blank">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++) {
java/lang/String.java.html" target="_blank">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 java/lang/String.java.html" target="_blank">String[]{"PICTURE"});
hub.publish(pub);
// Create two spokes and subscribe to this publication
for(int i=3;i<=4;i++) {
java/lang/String.java.html" target="_blank">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 java/lang/String.java.html" target="_blank">String spokename;
private int spoke_id;
private int spoke_range_start,spoke_range_end;
final static int ROWS_PER_SPOKE=1<<16;
private java/lang/String.java.html" target="_blank">String syncurl;
private java/lang/String.java.html" target="_blank">String syncpassword;
private DBManager() {
// Get DB connection parameters
// ... ...
// Get sync parameters
syncurl =
properties.getProperty("syncurl", "http://localhost:8124");
java/lang/String.java.html" target="_blank">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 {
java/lang/System.java.html" target="_blank">System.out.println("Connecting to the database...");
java/lang/Class.java.html" target="_blank">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 (java/lang/Exception.java.html" target="_blank">Exception e) {
e.printStackTrace();
java/lang/System.java.html" target="_blank">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 (java/lang/Exception.java.html" target="_blank">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) {
java/lang/System.java.html" target="_blank">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();
java/lang/System.java.html" target="_blank">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.
}
Resources
· Download the source code for this article’s PointBase ContactManager sample application (you need to download PointBase Micro database and UniSync to run the sample):
http://www.javaworld.com/javaworld/jw-06-2003/wireless/jw-0606-wireless.zip
· For more detailed discussion and complete source code analysis, preview Michael Yuan’s upcoming book, Java Mobile Enterprise Application Development:
http://www.enterprisej2me.com/books.php
· The JDBC specification:
http://java.sun.com/products/jdbc/
· The JDBC optional package:
http://java.sun.com/products/jdbc/download.html/#cdcfp
· The supported JDBC API in PersonalJava:
http://java.sun.com/products/personaljava/
· HSQL Database Engine (check out the Sharp Zaurus page):
http://hsqldb.sourceforge.net/
· Sybase iAnywhere Solution’s SQL Anywhere Studio (including Adaptive Server Anywhere and UltraLite deployment option):
http://www.sybase.com/products/mobilewireless/anywhere
· IBM DB2 Everyplace:
http://www-3.ibm.com/software/data/db2/everyplace/
· Oracle9i Lite database:
http://otn.oracle.com/products/lite/content.html
· PointBase Micro database and UniSync server:
http://www.pointbase.com/home.shtml
· For more articles on J2ME and wireless development, browse the Micro Java section of JavaWorld’s Topical Index:
http://www.javaworld.com/channel_content/jw-micro-index.shtml
· More Wireless Java articles:
http://www.javaworld.com/columns/jw-wireless-index.shtml
· Browse the Java Database Connectivity (JDBC) section of JavaWorld’s Topical Index:
http://www.javaworld.com/channel_content/jw-jdbc-index.shtml
· Michael Yuan also authored the following JavaWorld articles:
o "Build Database-Powered Mobile Applications on the Java Platform" (January 2002)
o "Track Wireless Sessions with J2ME/MIDP" (April 2002)
o "Java Tip 126: Prepare Cross-Server Database Access Methods with JDBC" (April 2002)
· Browse the Development Tools section of JavaWorld’s Topical Index:
http://www.javaworld.com/channel_content/jw-tools-index.shtml
· Browse JavaWorld’s Product Reviews index page:
http://www.javaworld.com/news-reviews/jw-nr-product-reviews.shtml
· Sign up for JavaWorld’s free weekly Micro Java email newsletter:
http://www.javaworld.com/subscribe
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高可靠性移动应用程序-移动数据库和J2ME工具(1)
高可靠性移动应用程序-移动数据库和J2ME工具(2)
高可靠性移动应用程序-移动数据库和J2ME工具(3)