在給出采用service方式實現的“扶貧助手”之前，我們稍微回顧一下上一篇的成果。
在（五）中，我們看到程序被分成多個bundle后，程序的模塊程度得到提高，而控制模塊間的耦合度由Import-Package和Export-Package來控制，相對比較靈活。另一方面程序的更新和升級的粒度變小了。誰都知道只更新部分要比全部更新強，尤其當更新發生在一些需要建立昂貴的連接時，細粒度會節省不少花銷。除了這些，我們看不到其他新鮮的東西。說白了，也就是挖空心思想一些design pattern來劃分程序模塊。
好了，馬上就新鮮了。下面你會看到通過采用service方式來改造（五）中的程序，gui bundle在某些情況下不用重新啟動，就能直接某些適應需求的變更！
先給出model bundle的代碼，該bundle包含兩個java package，分別是:
com.bajie.test.family.model
com.bajie.test.family.model.impl
在com.bajie.test.family.model這個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;
}
這是database的model，與（五）定義成interface不同，我們直接讓它繼承了AbstractTableModel，這是因為我們希望當數據或顯示需求變化時，gui上的JTable能獲得通知，并顯示更新的結果。SortingFamilyInfoCriteria這個類型下文會給出說明。
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;
}
}
這個類的結構和在（五）中完全一樣，用來紀錄一條家庭信息。唯一不同的是，在（五）中我們把它放入了實現(.impl)package中，在后面給出bundle的manifest文件時，我將解釋為什么要這樣改。
package com.bajie.test.family.model;
public interface FamilyInfoColumn {
public Object getColumnValue(FamilyInfoEntry entry);
public String getColumnName();
}
這個類用來描述table中的某個列。
package com.bajie.test.family.model;
import java.util.Comparator;
public interface SortingFamilyInfoCriteria extends Comparator{
public String getSortFieldString();
}
這個類將用于對家庭紀錄按某一列的值進行排序。
在com.bajie.test.family.model.impl這個package中包含上面抽象類和interface的實現：
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注冊一個類型為FamilyInfoDatabase的服務
context.registerService(FamilyInfoDatabase.class.getName(),this,null);
//向framework注冊三個服務，每個服務的類型既為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查找所有注冊類型為FamilyInfoColumn的服務
//先獲得服務的引用
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]);
//通過引用獲得具體的服務對象，每一個對象都將轉化成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.");
}
}
//注冊服務偵聽器，該偵聽器專門偵聽FamilyInfoColumn服務對象的動態（主要是增加和刪除）
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://表明有新的列產生了。
ServiceReference ref = event.getServiceReference();
Object service = this.context.getService(ref);
this.columns.add(service);
this.fireTableStructureChanged();//通知gui，表結構發生變化
return;
case ServiceEvent.UNREGISTERING://表明有些列將被刪除
ref = event.getServiceReference();
service = this.context.getService(ref);
this.columns.remove(service);
this.fireTableStructureChanged();//通知gui，表結構發生變化
return;
}
}
//這個類定義一個“Family Name”這個列，以及如何按這個列的值進行排序
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());
}
}
//這個類定義一個“Family Population”這個列，以及如何按這個列的值進行排序
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();
}
}
//這個類定義一個“Family Income”這個列，以及如何按這個列的值進行排序
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();
}
}
}
與（五）相比，最大的不同就是表結構的“列”是通過查找所有類型為FamilyInfoColumn的服務對象而組成的。而通過framework提供的服務偵聽機制（即實現ServiceListener接口并注冊到framework中），bundle能夠獲得該類服務對象的動態事件通知，如果該事件是新服務注冊，則添加一個顯示列，如果是服務被注銷，則刪除對應的顯示列。
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
從中我們看到com.bajie.test.family.model這個package被export出來，這樣其他bundle就能夠import這個package，并根據FamilyInfoEntry所提供的基本內容提供一些額外的處理結果，從而產生新列(FamilyInfoColumn)以及排序方法(SortingFamilyInfoCriteria)，比如家庭人均年收入。
下面來看看gui bundle，它只包含一個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;
//查找所有注冊類型為FamilyInfoDatabase的服務對象。在我們這個例子，它是由上面給出的model bundle注冊的
ServiceReference databaseServiceRef = context
.getServiceReference(FamilyInfoDatabase.class.getName());
if (databaseServiceRef == null) {
System.out.println("No database service is registered.");
return;
}
//這個服務對象將成為JTable的數據model
this.database = (FamilyInfoDatabase) context
.getService(databaseServiceRef);
if (this.database == null) {
System.out.println("Can not get database object");
return;
}
//查找所有注冊類型為SortingFamilyInfoCriteria的服務對象。
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) {
//每個服務對象將對應一種排序方法，并加入到下拉列表中
sortedByList.addItem(criterion.getSortFieldString());
this.sortingFields.put(criterion.getSortFieldString(),
criterion);
}
}
}
//注冊服務偵聽器，該偵聽器專門偵聽SortingFamilyInfoCriteria服務對象的動態（主要是增加和刪除）
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();
//獲得的FamilyInfoDatabase對象成為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://有新的排序方法注冊到framework當中
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://一個現有的排序方法將被從framework被取消
ref = event.getServiceReference();
criterion = (SortingFamilyInfoCriteria) this.context
.getService(ref);
if (criterion != null) {
//把該排序方法從下拉列表中刪除
sortedByList.removeItem(criterion.getSortFieldString());
this.sortingFields.remove(criterion);
}
return;
}
}
}
與（五）相比不同的地方是，這個gui的table model以及排序的方法，都是通過查詢service對象獲得。
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
然后我們生成bundle的jar文件。分別為familymodel.jar和familygui.jar，之后我們用“in”命令把兩個bundle裝入framework。
接著我們先啟動model bundle，然后再啟動gui bundle，我們會看到JTable中有3列，而排序方法列表中也有3個選項，完全和程序的邏輯符合。
接下來，我們假設客戶需要添加顯示每個家庭的人均年收入并按其排列紀錄。要滿足這個需求，我們可以參考在（五）中做法，就是在model bundle里面再添加一個同時實現了FamilyInfoColumn和SortingFamilyInfoCriteria的類，并在bundle的啟動中作為服務注冊到framework中？不過這樣就得更新model bundle然后調用rfr命令來刷新。為什么不再裝一個補丁bundle，在這個bundle中包含了同時實現FamilyInfoColumn和SortingFamilyInfoCriteria的類，并在這個新bunle啟動時注冊產生該類的新對象作為服務注冊到framework中，這樣gui和model bundle都能偵聽到該新服務的到來(他們都實現了服務偵聽接口ServiceListener)，gui上馬上就能有所體現。
這個新bundle的代碼如下：
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 {
//注冊一個新的服務，服務的類型既為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 {
}
//這個類實現了“Income Per Person”這個列以及按該列排序的方法。
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
打包安裝到framework后，啟動該bundle，我們就會在gui上看到新的列已經被添加，而且排序列表中增加了一個新的排序選項。
這個結果，完全符合需求的意圖。
如果我們用stp命令停止這個bundle，我們在gui上就會發現，新列消失，而且排序列表中對應選項也沒有了。這就是service帶來的動態效果。不過，如果我們的model發生了一些實質的變化，比如FamilyInfoEntry需要添加一個“地址”列，那么model bundle就要更新，進而gui bundle以及使用到這個類型的bundle都需要通過rfr命令刷新。
好了，對扶貧助手的分析就此打住，我們總結一下，通過程序可以看到注冊服務一點都不復雜。最簡單的情況我們只需要提供一個java類型名稱，以及實現這個類型的一個java對象就可以了，
不需要提供復雜的類型描述，比如xml描述文件。而使用服務的bundle通過類型名稱就輕而易舉的查找到相關的服務對象。
到此，osig介紹系列就要結束了，只希望這個系列能夠把你引入到osgi的門口，其后面的精彩世界就看你的興趣了。
就我個人的關注和理解，今年是osgi很重要的一年。JSR249今年應該投票，如果osgi入選，那么osgi將成為高端手機中java體系結構的重要組成部分。
在汽車領域，siemensVDO已經推出了基于osgi的解決方案，聽說已經配備在BMW serials 5里面了。應該還會有更多的應用......