在給出采用service方式實(shí)現(xiàn)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(gè)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(lái)控制，相對(duì)比較靈活。另一方面程序的更新和升級(jí)的粒度變小了。誰(shuí)都知道只更新部分要比全部更新強(qiáng)，尤其當(dāng)更新發(fā)生在一些需要建立昂貴的連接時(shí)，細(xì)粒度會(huì)節(jié)省不少花銷(xiāo)。除了這些，我們看不到其他新鮮的東西。說(shuō)白了，也就是挖空心思想一些design pattern來(lái)劃分程序模塊。
好了，馬上就新鮮了。下面你會(huì)看到通過(guò)采用service方式來(lái)改造（五）中的程序，gui bundle在某些情況下不用重新啟動(dòng)，就能直接某些適應(yīng)需求的變更！
先給出model bundle的代碼，該bundle包含兩個(gè)java package，分別是:
com.bajie.test.family.model
com.bajie.test.family.model.impl
在com.bajie.test.family.model這個(gè)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?yàn)槲覀兿Ｍ?dāng)數(shù)據(jù)或顯示需求變化時(shí)，gui上的JTable能獲得通知，并顯示更新的結(jié)果。SortingFamilyInfoCriteria這個(gè)類型下文會(huì)給出說(shuō)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(gè)類的結(jié)構(gòu)和在（五）中完全一樣，用來(lái)紀(jì)錄一條家庭信息。唯一不同的是，在（五）中我們把它放入了實(shí)現(xiàn)(.impl)package中，在后面給出bundle的manifest文件時(shí)，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(gè)類用來(lái)描述table中的某個(gè)列。
package com.bajie.test.family.model;
import java.util.Comparator;
public interface SortingFamilyInfoCriteria extends Comparator{
public String getSortFieldString();
}
這個(gè)類將用于對(duì)家庭紀(jì)錄按某一列的值進(jìn)行排序。
在com.bajie.test.family.model.impl這個(gè)package中包含上面抽象類和interface的實(shí)現(xiàn)：
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(cè)一個(gè)類型為FamilyInfoDatabase的服務(wù)
context.registerService(FamilyInfoDatabase.class.getName(),this,null);
//向framework注冊(cè)三個(gè)服務(wù)，每個(gè)服務(wù)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(cè)類型為FamilyInfoColumn的服務(wù)
//先獲得服務(wù)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(guò)引用獲得具體的服務(wù)對(duì)象，每一個(gè)對(duì)象都將轉(zhuǎn)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(cè)服務(wù)偵聽(tīng)器，該偵聽(tīng)器專門(mén)偵聽(tīng)FamilyInfoColumn服務(wù)對(duì)象的動(dòng)態(tài)（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(chǎn)生了。
ServiceReference ref = event.getServiceReference();
Object service = this.context.getService(ref);
this.columns.add(service);
this.fireTableStructureChanged();//通知gui，表結(jié)構(gòu)發(fā)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(jié)構(gòu)發(fā)生變化
return;
}
}
//這個(gè)類定義一個(gè)“Family Name”這個(gè)列，以及如何按這個(gè)列的值進(jìn)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(gè)類定義一個(gè)“Family Population”這個(gè)列，以及如何按這個(gè)列的值進(jìn)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(gè)類定義一個(gè)“Family Income”這個(gè)列，以及如何按這個(gè)列的值進(jìn)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(jié)構(gòu)的“列”是通過(guò)查找所有類型為FamilyInfoColumn的服務(wù)對(duì)象而組成的。而通過(guò)framework提供的服務(wù)偵聽(tīng)機(jī)制（即實(shí)現(xiàn)ServiceListener接口并注冊(cè)到framework中），bundle能夠獲得該類服務(wù)對(duì)象的動(dòng)態(tài)事件通知，如果該事件是新服務(wù)注冊(cè)，則添加一個(gè)顯示列，如果是服務(wù)被注銷(xiāo)，則刪除對(duì)應(yīng)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(gè)package被export出來(lái)，這樣其他bundle就能夠import這個(gè)package，并根據(jù)FamilyInfoEntry所提供的基本內(nèi)容提供一些額外的處理結(jié)果，從而產(chǎn)生新列(FamilyInfoColumn)以及排序方法(SortingFamilyInfoCriteria)，比如家庭人均年收入。
下面來(lái)看看gui bundle，它只包含一個(gè)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(cè)類型為FamilyInfoDatabase的服務(wù)對(duì)象。在我們這個(gè)例子，它是由上面給出的model bundle注冊(cè)的
ServiceReference databaseServiceRef = context
.getServiceReference(FamilyInfoDatabase.class.getName());
if (databaseServiceRef == null) {
System.out.println("No database service is registered.");
return;
}
//這個(gè)服務(wù)對(duì)象將成為JTable的數(shù)據(jù)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(cè)類型為SortingFamilyInfoCriteria的服務(wù)對(duì)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(gè)服務(wù)對(duì)象將對(duì)應(yīng)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(cè)服務(wù)偵聽(tīng)器，該偵聽(tīng)器專門(mén)偵聽(tīng)SortingFamilyInfoCriteria服務(wù)對(duì)象的動(dòng)態(tài)（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(duì)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(cè)到framework當(dāng)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(gè)現(xiàn)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(gè)gui的table model以及排序的方法，都是通過(guò)查詢service對(duì)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(gè)bundle裝入framework。
接著我們先啟動(dòng)model bundle，然后再啟動(dòng)gui bundle，我們會(huì)看到JTable中有3列，而排序方法列表中也有3個(gè)選項(xiàng)，完全和程序的邏輯符合。
接下來(lái)，我們假設(shè)客戶需要添加顯示每個(gè)家庭的人均年收入并按其排列紀(jì)錄。要滿足這個(gè)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(gè)同時(shí)實(shí)現(xiàn)了FamilyInfoColumn和SortingFamilyInfoCriteria的類，并在bundle的啟動(dòng)中作為服務(wù)注冊(cè)到framework中？不過(guò)這樣就得更新model bundle然后調(diào)用rfr命令來(lái)刷新。為什么不再裝一個(gè)補(bǔ)丁bundle，在這個(gè)bundle中包含了同時(shí)實(shí)現(xiàn)FamilyInfoColumn和SortingFamilyInfoCriteria的類，并在這個(gè)新bunle啟動(dòng)時(shí)注冊(cè)產(chǎn)生該類的新對(duì)象作為服務(wù)注冊(cè)到framework中，這樣gui和model bundle都能偵聽(tīng)到該新服務(wù)的到來(lái)(他們都實(shí)現(xiàn)了服務(wù)偵聽(tīng)接口ServiceListener)，gui上馬上就能有所體現(xiàn)。
這個(gè)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(cè)一個(gè)新的服務(wù)，服務(wù)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(gè)類實(shí)現(xiàn)了“Income Per Person”這個(gè)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(dòng)該bundle，我們就會(huì)在gui上看到新的列已經(jīng)被添加，而且排序列表中增加了一個(gè)新的排序選項(xiàng)。
這個(gè)結(jié)果，完全符合需求的意圖。
如果我們用stp命令停止這個(gè)bundle，我們?cè)趃ui上就會(huì)發(fā)現(xiàn)，新列消失，而且排序列表中對(duì)應(yīng)選項(xiàng)也沒(méi)有了。這就是service帶來(lái)的動(dòng)態(tài)效果。不過(guò)，如果我們的model發(fā)生了一些實(shí)質(zhì)的變化，比如FamilyInfoEntry需要添加一個(gè)“地址”列，那么model bundle就要更新，進(jìn)而gui bundle以及使用到這個(gè)類型的bundle都需要通過(guò)rfr命令刷新。
好了，對(duì)扶貧助手的分析就此打住，我們總結(jié)一下，通過(guò)程序可以看到注冊(cè)服務(wù)一點(diǎn)都不復(fù)雜。最簡(jiǎn)單的情況我們只需要提供一個(gè)java類型名稱，以及實(shí)現(xiàn)這個(gè)類型的一個(gè)java對(duì)象就可以了，
不需要提供復(fù)雜的類型描述，比如xml描述文件。而使用服務(wù)的bundle通過(guò)類型名稱就輕而易舉的查找到相關(guān)的服務(wù)對(duì)象。
到此，osig介紹系列就要結(jié)束了，只希望這個(gè)系列能夠把你引入到osgi的門(mén)口，其后面的精彩世界就看你的興趣了。
就我個(gè)人的關(guān)注和理解，今年是osgi很重要的一年。JSR249今年應(yīng)該投票，如果osgi入選，那么osgi將成為高端手機(jī)中java體系結(jié)構(gòu)的重要組成部分。
在汽車(chē)領(lǐng)域，siemensVDO已經(jīng)推出了基于osgi的解決方案，聽(tīng)說(shuō)已經(jīng)配備在BMW serials 5里面了。應(yīng)該還會(huì)有更多的應(yīng)用......