在给出采用service方式实现的“扶贫助手”之前，我们稍微回顾一下上一篇的成果。
在（五）中，我们看到程序被分成多个bundle后，程序的模块程度得到提高，而控制模块间的耦合度由Import-Package和Export-Package来控制，相对比较灵活。另一方面程序的更新和升级的粒度变小了。谁都知道只更新部分要比全部更新强，尤其当更新发生在一些需要建立昂贵的连接时，细粒度会节省不少花销。除了这些，我们看不到其他新鲜的东西。说白了，也就是挖空心思想一些design pattern来划分程序模块。
好了，马上就新鲜了。下面你会看到通过采用service方式来改造（五）中的程序，gui bundle在某些情况下不用重新启动，就能直接某些适应需求的变更！
先给出model bundle的代码，该bundle包含两个java package，分别是:
com.bajie.test.family.model
com.bajie.test.family.model.impl
在com.bajie.test.family.model这个package中包含如下的class和interface:
package com.bajie.test.family.model;
import java.util.List;
import javax.swing.table.AbstractTableModel;
public abstract class FamilyInfoDatabase extends AbstractTableModel{
public abstract void sort(SortingFamilyInfoCriteria sortField) throws IllegalArgumentException;
public abstract void addEntry(List columns, List values) throws IllegalArgumentException;
public abstract void deleteEntry(String familyName);
public abstract void update(String familyName,List columns, List values)throws IllegalArgumentException;
}
这是database的model，与（五）定义成interface不同，我们直接让它继承了AbstractTableModel，这是因为我们希望当数据或显示需求变化时，gui上的JTable能获得通知，并显示更新的结果。SortingFamilyInfoCriteria这个类型下文会给出说明。
package com.bajie.test.family.model;
public class FamilyInfoEntry {
private String familyName;
private int population;
private int incomePerYear;
public FamilyInfoEntry(String familyName,int population,int income){
this.familyName = familyName;
this.population = population;
this.incomePerYear = income;
}
public String getFamilyName() {
return familyName;
}
public int getIncomePerYear() {
return incomePerYear;
}
public int getPopulation() {
return population;
}
}
这个类的结构和在（五）中完全一样，用来纪录一条家庭信息。唯一不同的是，在（五）中我们把它放入了实现(.impl)package中，在后面给出bundle的manifest文件时，我将解释为什么要这样改。
package com.bajie.test.family.model;
public interface FamilyInfoColumn {
public Object getColumnValue(FamilyInfoEntry entry);
public String getColumnName();
}
这个类用来描述table中的某个列。
package com.bajie.test.family.model;
import java.util.Comparator;
public interface SortingFamilyInfoCriteria extends Comparator{
public String getSortFieldString();
}
这个类将用于对家庭纪录按某一列的值进行排序。
在com.bajie.test.family.model.impl这个package中包含上面抽象类和interface的实现：
package com.bajie.test.family.model.impl;
import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;
import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;
import org.osgi.framework.Constants;
import org.osgi.framework.ServiceEvent;
import org.osgi.framework.ServiceListener;
import org.osgi.framework.ServiceReference;
import com.bajie.test.family.model.FamilyInfoColumn;
import com.bajie.test.family.model.FamilyInfoDatabase;
import com.bajie.test.family.model.FamilyInfoEntry;
import com.bajie.test.family.model.SortingFamilyInfoCriteria;
public class FamilyDatabase extends FamilyInfoDatabase implements BundleActivator,
ServiceListener {
private LinkedList familyEntryList = new LinkedList();
private Object[] sortedValues = null;
private LinkedList columns = new LinkedList();
private BundleContext context;
public int getColumnCount() {
return this.columns.size();
}
public String getColumnName(int index) {
return ((FamilyInfoColumn)columns.get(index)).getColumnName();
}
public Object getValueAt(int row, int column) {
FamilyInfoEntry entry = (FamilyInfoEntry) this.sortedValues[row];
if(column >= this.familyEntryList.size()){
return null;
}
return ((FamilyInfoColumn) this.columns.get(column))
.getColumnValue(entry);
}
public int getRowCount() {
return this.familyEntryList.size();
}
public void addEntry(List columns, List values)
throws IllegalArgumentException {
}
public void deleteEntry(String familyName) {
}
public void update(String familyName, List columns, List values)
throws IllegalArgumentException {
}
public void sort(SortingFamilyInfoCriteria sortField) {
Arrays.sort(this.sortedValues, sortField);
}
public void start(BundleContext context) throws Exception {
this.context = context;
this.familyEntryList.add(new FamilyInfoEntry("Zhang", 3, 1200));
this.familyEntryList.add(new FamilyInfoEntry("Li", 6, 1800));
this.familyEntryList.add(new FamilyInfoEntry("Liu", 5, 1500));
this.familyEntryList.add(new FamilyInfoEntry("Wang", 4, 1300));
this.sortedValues = this.familyEntryList.toArray();
//向framework注册一个类型为FamilyInfoDatabase的服务
context.registerService(FamilyInfoDatabase.class.getName(),this,null);
//向framework注册三个服务，每个服务的类型既为FamilyInfoColumn，也是SortingFamilyInfoCriteria
String[] clazzes = new String[] {FamilyInfoColumn.class.getName(),SortingFamilyInfoCriteria.class.getName()};
context.registerService(clazzes,new FamilyNameColumn(),null);
context.registerService(clazzes,new FamilyPopulationColumn(),null);
context.registerService(clazzes,new FamilyIncomeColumn(),null);
//向framework查找所有注册类型为FamilyInfoColumn的服务
//先获得服务的引用
ServiceReference[] columnRefs = context.getServiceReferences(
FamilyInfoColumn.class.getName(), null);
FamilyInfoColumn column = null;
for (int i = 0; i < columnRefs.length; i++) {
System.out.println(i + ":" + ((String[])(columnRefs[i].getProperty(Constants.OBJECTCLASS)))[0]);
//通过引用获得具体的服务对象，每一个对象都将转化成gui中table的一列
column = (FamilyInfoColumn) context.getService(columnRefs[i]);
if (column != null) {
this.columns.add(column);
}else{
System.out.println("null service object.");
}
}
//注册服务侦听器，该侦听器专门侦听FamilyInfoColumn服务对象的动态（主要是增加和删除）
context.addServiceListener(this，"(" + Constants.OBJECTCLASS + "="
+ FamilyInfoColumn.class.getName() + ")");
}
public void stop(BundleContext context) throws Exception {
}
public void serviceChanged(ServiceEvent event) {
switch (event.getType()) {
case ServiceEvent.MODIFIED:
return;
case ServiceEvent.REGISTERED://表明有新的列产生了。
ServiceReference ref = event.getServiceReference();
Object service = this.context.getService(ref);
this.columns.add(service);
this.fireTableStructureChanged();//通知gui，表结构发生变化
return;
case ServiceEvent.UNREGISTERING://表明有些列将被删除
ref = event.getServiceReference();
service = this.context.getService(ref);
this.columns.remove(service);
this.fireTableStructureChanged();//通知gui，表结构发生变化
return;
}
}
//这个类定义一个“Family Name”这个列，以及如何按这个列的值进行排序
class FamilyNameColumn implements FamilyInfoColumn,SortingFamilyInfoCriteria {
private static final String COLUMNNAME = "Family Name";
public Object getColumnValue(FamilyInfoEntry entry) {
return entry.getFamilyName();
}
public String getColumnName() {
return FamilyNameColumn.COLUMNNAME;
}
public String getSortFieldString() {
return FamilyNameColumn.COLUMNNAME;
}
public int compare(Object obj1, Object obj2) {
if (obj1 == obj2) {
return 0;
}
FamilyInfoEntry en1 = (FamilyInfoEntry)obj1;
FamilyInfoEntry en2 = (FamilyInfoEntry)obj2;
return en1.getFamilyName().compareTo(en2.getFamilyName());
}
}
//这个类定义一个“Family Population”这个列，以及如何按这个列的值进行排序
class FamilyPopulationColumn implements FamilyInfoColumn, SortingFamilyInfoCriteria {
private static final String COLUMNNAME = "Family Population";
public Object getColumnValue(FamilyInfoEntry entry) {
return new Integer(entry.getPopulation());
}
public String getColumnName() {
return FamilyPopulationColumn.COLUMNNAME;
}
public String getSortFieldString() {
return FamilyPopulationColumn.COLUMNNAME;
}
public int compare(Object obj1, Object obj2) {
if (obj1 == obj2) {
return 0;
}
FamilyInfoEntry en1 = (FamilyInfoEntry)obj1;
FamilyInfoEntry en2 = (FamilyInfoEntry)obj2;
return en1.getPopulation() - en2.getPopulation();
}
}
//这个类定义一个“Family Income”这个列，以及如何按这个列的值进行排序
class FamilyIncomeColumn implements FamilyInfoColumn, SortingFamilyInfoCriteria {
private static final String COLUMNNAME = "Family Income";
public Object getColumnValue(FamilyInfoEntry entry) {
return new Integer(entry.getIncomePerYear());
}
public String getColumnName() {
return FamilyIncomeColumn.COLUMNNAME;
}
public String getSortFieldString() {
return FamilyIncomeColumn.COLUMNNAME;
}
public int compare(Object obj1, Object obj2) {
if (obj1 == obj2) {
return 0;
}
FamilyInfoEntry en1 = (FamilyInfoEntry)obj1;
FamilyInfoEntry en2 = (FamilyInfoEntry)obj2;
return en1.getIncomePerYear() - en2.getIncomePerYear();
}
}
}
与（五）相比，最大的不同就是表结构的“列”是通过查找所有类型为FamilyInfoColumn的服务对象而组成的。而通过framework提供的服务侦听机制（即实现ServiceListener接口并注册到framework中），bundle能够获得该类服务对象的动态事件通知，如果该事件是新服务注册，则添加一个显示列，如果是服务被注销，则删除对应的显示列。
下面是bundle的manifest文件
Manifest-Version: 1.0
Bundle-SymbolicName: com.bajie.test.family.model
Bundle-Name: family model
Bundle-Version: 1.0
Bundle-Vendor: LiMing
Bundle-Activator: com.bajie.test.family.model.impl.FamilyDatabase
Import-Package: org.osgi.framework;version=1.3,com.bajie.test.family.model
Export-Package: com.bajie.test.family.model;version=1.0
从中我们看到com.bajie.test.family.model这个package被export出来，这样其他bundle就能够import这个package，并根据FamilyInfoEntry所提供的基本内容提供一些额外的处理结果，从而产生新列(FamilyInfoColumn)以及排序方法(SortingFamilyInfoCriteria)，比如家庭人均年收入。
下面来看看gui bundle，它只包含一个package
package com.bajie.test.family.gui;
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.util.Hashtable;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;
import org.osgi.framework.Constants;
import org.osgi.framework.ServiceEvent;
import org.osgi.framework.ServiceListener;
import org.osgi.framework.ServiceReference;
import com.bajie.test.family.model.FamilyInfoDatabase;
import com.bajie.test.family.model.SortingFamilyInfoCriteria;
public class FamilyInfoGui implements BundleActivator, ActionListener,
ItemListener, ServiceListener {
private JFrame mainFrame;
private JPanel contentPanel;
private JTable familiesTable;
private JScrollPane familiesTableScrollPane;
private JPanel sortedByPanel = new JPanel(new GridLayout(1, 2));
private JLabel sortedByLabel = new JLabel("Sorted By: ");
private JComboBox sortedByList = null;
private JPanel commandPanel = new JPanel(new GridLayout(1, 3));
private JButton addEntry = new JButton("Add");
private JButton deleteEntry = new JButton("Delete");
private JButton updateEntry = new JButton("Update");
private Hashtable sortingFields = new Hashtable();
private BundleContext context;
FamilyInfoDatabase database = null;
public void start(BundleContext context) throws Exception {
this.context = context;
//查找所有注册类型为FamilyInfoDatabase的服务对象。在我们这个例子，它是由上面给出的model bundle注册的
ServiceReference databaseServiceRef = context
.getServiceReference(FamilyInfoDatabase.class.getName());
if (databaseServiceRef == null) {
System.out.println("No database service is registered.");
return;
}
//这个服务对象将成为JTable的数据model
this.database = (FamilyInfoDatabase) context
.getService(databaseServiceRef);
if (this.database == null) {
System.out.println("Can not get database object");
return;
}
//查找所有注册类型为SortingFamilyInfoCriteria的服务对象。
ServiceReference[] sortingCriteria = context.getServiceReferences(
SortingFamilyInfoCriteria.class.getName(), null);
sortedByList = new JComboBox();
SortingFamilyInfoCriteria criterion = null;
if (sortingCriteria != null) {
for (int i = 0; i < sortingCriteria.length; i++) {
criterion = (SortingFamilyInfoCriteria) context
.getService(sortingCriteria[i]);
if (criterion != null) {
//每个服务对象将对应一种排序方法，并加入到下拉列表中
sortedByList.addItem(criterion.getSortFieldString());
this.sortingFields.put(criterion.getSortFieldString(),
criterion);
}
}
}
//注册服务侦听器，该侦听器专门侦听SortingFamilyInfoCriteria服务对象的动态（主要是增加和删除）
context.addServiceListener(this, "(" + Constants.OBJECTCLASS + "="
+ SortingFamilyInfoCriteria.class.getName() + ")");
sortedByList.addItemListener(FamilyInfoGui.this);
//construct gui
Runnable r = new Runnable() {
public void run() {
contentPanel = new JPanel();
familiesTableScrollPane = new JScrollPane();
//获得的FamilyInfoDatabase对象成为gui中JTable的model
familiesTable = new JTable(database);
familiesTableScrollPane.setViewportView(familiesTable);
sortedByPanel.add(sortedByLabel);
sortedByPanel.add(sortedByList);
commandPanel.add(addEntry);
commandPanel.add(deleteEntry);
commandPanel.add(updateEntry);
contentPanel.add(sortedByPanel, BorderLayout.NORTH);
contentPanel.add(familiesTableScrollPane, BorderLayout.CENTER);
contentPanel.add(commandPanel, BorderLayout.SOUTH);
mainFrame = new JFrame();
mainFrame.setContentPane(contentPanel);
mainFrame.setSize(new Dimension(500, 600));
mainFrame.show();
}
};
Thread t = new Thread(r);
t.start();
}
public void stop(BundleContext context) throws Exception {
if (this.mainFrame != null)
this.mainFrame.dispose();
}
public void actionPerformed(ActionEvent event) {
}
public void itemStateChanged(ItemEvent event) {
if (event.getSource() == this.sortedByList) {
SortingFamilyInfoCriteria criterion = (SortingFamilyInfoCriteria) this.sortingFields
.get(event.getItem());
if (criterion == null)
return;
this.database.sort(criterion);
this.familiesTable.repaint();
}
}
public void serviceChanged(ServiceEvent event) {
switch (event.getType()) {
case ServiceEvent.MODIFIED:
return;
case ServiceEvent.REGISTERED://有新的排序方法注册到framework当中
ServiceReference ref = event.getServiceReference();
SortingFamilyInfoCriteria criterion = (SortingFamilyInfoCriteria) this.context
.getService(ref);
if (criterion != null) {
//把新的排序方法加入到下拉列表中
sortedByList.addItem(criterion.getSortFieldString());
this.sortingFields.put(criterion.getSortFieldString(),
criterion);
}
return;
case ServiceEvent.UNREGISTERING://一个现有的排序方法将被从framework被取消
ref = event.getServiceReference();
criterion = (SortingFamilyInfoCriteria) this.context
.getService(ref);
if (criterion != null) {
//把该排序方法从下拉列表中删除
sortedByList.removeItem(criterion.getSortFieldString());
this.sortingFields.remove(criterion);
}
return;
}
}
}
与（五）相比不同的地方是，这个gui的table model以及排序的方法，都是通过查询service对象获得。
manifest文件如下：
Manifest-Version: 1.0
Bundle-SymbolicName: com.bajie.test.family.gui
Bundle-Name: family gui
Bundle-Version: 1.0
Bundle-Vendor: LiMing
Bundle-Activator: com.bajie.test.family.gui.FamilyInfoGui
Import-Package: org.osgi.framework;version=1.3,com.bajie.test.family.model
然后我们生成bundle的jar文件。分别为familymodel.jar和familygui.jar，之后我们用“in”命令把两个bundle装入framework。
接着我们先启动model bundle，然后再启动gui bundle，我们会看到JTable中有3列，而排序方法列表中也有3个选项，完全和程序的逻辑符合。
接下来，我们假设客户需要添加显示每个家庭的人均年收入并按其排列纪录。要满足这个需求，我们可以参考在（五）中做法，就是在model bundle里面再添加一个同时实现了FamilyInfoColumn和SortingFamilyInfoCriteria的类，并在bundle的启动中作为服务注册到framework中？不过这样就得更新model bundle然后调用rfr命令来刷新。为什么不再装一个补丁bundle，在这个bundle中包含了同时实现FamilyInfoColumn和SortingFamilyInfoCriteria的类，并在这个新bunle启动时注册产生该类的新对象作为服务注册到framework中，这样gui和model bundle都能侦听到该新服务的到来(他们都实现了服务侦听接口ServiceListener)，gui上马上就能有所体现。
这个新bundle的代码如下：
package com.bajie.test.family.model.impladd;
import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;
import com.bajie.test.family.model.FamilyInfoColumn;
import com.bajie.test.family.model.FamilyInfoEntry;
import com.bajie.test.family.model.SortingFamilyInfoCriteria;
public class FamilyIncomePerPerson implements BundleActivator {
public void start(BundleContext context) throws Exception {
//注册一个新的服务，服务的类型既为FamilyInfoColumn，也是SortingFamilyInfoCriteria
String[] clazzes = new String[] {FamilyInfoColumn.class.getName(),SortingFamilyInfoCriteria.class.getName()};
context.registerService(clazzes,new FamilyIncomePerPersonColumn(),null);
}
public void stop(BundleContext context) throws Exception {
}
//这个类实现了“Income Per Person”这个列以及按该列排序的方法。
class FamilyIncomePerPersonColumn implements FamilyInfoColumn,SortingFamilyInfoCriteria {
private static final String COLUMNNAME = "Income Per Person";
public Object getColumnValue(FamilyInfoEntry entry) {
return new Integer(entry.getIncomePerYear()/entry.getPopulation());
}
public String getColumnName() {
return FamilyIncomePerPersonColumn.COLUMNNAME;
}
public String getSortFieldString() {
return FamilyIncomePerPersonColumn.COLUMNNAME;
}
public int compare(Object obj1, Object obj2) {
if (obj1 == obj2) {
return 0;
}
FamilyInfoEntry en1 = (FamilyInfoEntry)obj1;
FamilyInfoEntry en2 = (FamilyInfoEntry)obj2;
return en1.getIncomePerYear()/en1.getPopulation() - en2.getIncomePerYear()/en2.getPopulation();
}
}
}
manifest文件如下：
Manifest-Version: 1.0
Bundle-SymbolicName: com.bajie.test.family.modeladd
Bundle-Name: family model add
Bundle-Version: 1.0
Bundle-Vendor: LiMing
Bundle-Activator: com.bajie.test.family.model.impladd.FamilyIncomePerPerson
Import-Package: org.osgi.framework;version=1.3,com.bajie.test.family.model
打包安装到framework后，启动该bundle，我们就会在gui上看到新的列已经被添加，而且排序列表中增加了一个新的排序选项。
这个结果，完全符合需求的意图。
如果我们用stp命令停止这个bundle，我们在gui上就会发现，新列消失，而且排序列表中对应选项也没有了。这就是service带来的动态效果。不过，如果我们的model发生了一些实质的变化，比如FamilyInfoEntry需要添加一个“地址”列，那么model bundle就要更新，进而gui bundle以及使用到这个类型的bundle都需要通过rfr命令刷新。
好了，对扶贫助手的分析就此打住，我们总结一下，通过程序可以看到注册服务一点都不复杂。最简单的情况我们只需要提供一个java类型名称，以及实现这个类型的一个java对象就可以了，
不需要提供复杂的类型描述，比如xml描述文件。而使用服务的bundle通过类型名称就轻而易举的查找到相关的服务对象。
到此，osig介绍系列就要结束了，只希望这个系列能够把你引入到osgi的门口，其后面的精彩世界就看你的兴趣了。
就我个人的关注和理解，今年是osgi很重要的一年。JSR249今年应该投票，如果osgi入选，那么osgi将成为高端手机中java体系结构的重要组成部分。
在汽车领域，siemensVDO已经推出了基于osgi的解决方案，听说已经配备在BMW serials 5里面了。应该还会有更多的应用......