浅析OSGI的bundle依赖
From: http://www.xeclipse.com/?p=1165
Bundle是OSGI中的基础元件，不同的bundle之间可以相互依赖、引用，这样许多bundle才会共同协作，实现一些比较复杂的功能。Bundle的依赖一直是一个比较棘手的问题，包括Lazy start等，下面我们具体Bundle依赖到底是怎么一回事。
测试场景：Eclipse 3.6， Equinox
先看看基础的依赖问题
准备环境
新建2个插件，注意选择“An OSGI Framework”
新建2个基础plugin project：org.salever.osgi.depends.clientbundle、org.salever.osgi.depends.hostbundle
然后启动一个OSGI Framework，在Eclipse里面Run configuration里面，新建一个OSGI Framework：
在新建的OSGI Framework里面，仅选择新建的2个插件，然后点击add Required Bundles：
为了测试顺利，建议添加-clean参数：
如果不出意外，将会出现OSGI的控制台：
输入ss，将列举当前的bundles：
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osgi> ss
Framework is launched.
id State Bundle
0
ACTIVE org.eclipse.osgi_3.
6.2
.R36x_v20110210
1
ACTIVE org.salever.osgi.depends.hostbundle_1.
0.0
.qualifier
2
ACTIVE org.salever.osgi.depends.clientbundle_1.
0.0
.qualifier
|
这时候仅仅有三个bundle启动，下面我们将尝试添加依赖关系，然后看看依赖关系不满足的时候，bundle的表现。
依赖
我们将尝试几种不同的场景：
- 【LAZY下】依赖不满足的时候，bundle的行为
- 正常运行的bundle，强行停止其依赖的bundles，该bundle的行为
- 无依赖的情况下，bundle的行为
在测试之前，必须先把OSGI Framework配置改下，将所有的bundle该为Lazy start，不然影响测试结果。
注意红线部分的设置。然后重启OSGI Framework。出现以下的内容，表明此时所有的bundle都是Lazy-start并且没有启动：
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osgi> ss
Framework is launched.
id State Bundle
0
ACTIVE org.eclipse.osgi_3.
6.2
.R36x_v20110210
3
<<LAZY>> org.salever.osgi.depends.hostbundle_1.
0.0
.qualifier
4
<<LAZY>> org.salever.osgi.depends.clientbundle_1.
0.0
.qualifier
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注意先要把Bundle都设为Lazy-start。实现Lazy-start的bundle很简单，在MANIFEST.MF中，添加
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Bundle-ActivationPolicy: lazy
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就可以了。
测试场景1——简单依赖
这时候修改新建的2个bundle，在org.salever.osgi.depends.clientbundle中添加对org.salever.osgi.depends.hostbundle的依赖：
保存重启OSGI Framework，然后尝试启动org.salever.osgi.depends.clientbundle
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osgi> ss
Framework is launched.
id State Bundle
0
ACTIVE org.eclipse.osgi_3.
6.2
.R36x_v20110210
3
<<LAZY>> org.salever.osgi.depends.hostbundle_1.
0.0
.qualifier
5
<<LAZY>> org.salever.osgi.depends.clientbundle_1.
0.0
.qualifier
osgi> start
5
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然后看看运行效果：
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osgi> ss
Framework is launched.
id State Bundle
0
ACTIVE org.eclipse.osgi_3.
6.2
.R36x_v20110210
3
<<LAZY>> org.salever.osgi.depends.hostbundle_1.
0.0
.qualifier
5
ACTIVE org.salever.osgi.depends.clientbundle_1.
0.0
.qualifier
osgi>
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这时候org.salever.osgi.depends.clientbundle已经启动，而依赖的bundle——org.salever.osgi.depends.hostbundle依然是
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3
<<LAZY>> org.salever.osgi.depends.hostbundle_1.
0.0
.qualifier
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看看clientbundle的header信息：
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osgi> headers
5
Bundle headers:
Bundle-ActivationPolicy = lazy
Bundle-Activator = org.salever.osgi.depends.clientbundle.Activator
Bundle-ManifestVersion =
2
Bundle-Name = Clientbundle
Bundle-RequiredExecutionEnvironment = JavaSE-
1.6
Bundle-SymbolicName = org.salever.osgi.depends.clientbundle;singleton:=
true
Bundle-Version =
1.0
.
0
.qualifier
Import-Package = org.osgi.framework;version=
"1.3.0"
Manifest-Version =
1.0
Require-Bundle = org.salever.osgi.depends.hostbundle;bundle-version=
"1.0.0"
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这时候尝试停止hostbundle：
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osgi> stop
3
osgi> ss
Framework is launched.
id State Bundle
0
ACTIVE org.eclipse.osgi_3.
6.2
.R36x_v20110210
3
RESOLVED org.salever.osgi.depends.hostbundle_1.
0.0
.qualifier
5
ACTIVE org.salever.osgi.depends.clientbundle_1.
0.0
.qualifier
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说明了即使被依赖的bundle不启动，clientbundle亦一样可以启动。
这里的依赖仅仅是简单的Add Required Bundle，没有使用里面的具体类，如果使用了依赖的bundle中的类了么？
测试场景2——添加具体Class调用
在hostbundle中新建类HostService：
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package
org.salever.osgi.depends.hostbundle;
/**
* @author LiXP
*
*/
public
class
HostService {
public
static
void
service() {
System.out.println(HostService.
class
.toString() +
": Service"
);
}
}
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然后Export这个package，使其能被其他bundle使用：
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Export-Package: org.salever.osgi.depends.hostbundle
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最后在clientbundle中添加使用，修改ClientActivator.java,使其在启动的时候调用
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/*
* (non-Javadoc)
*
* @see
* org.osgi.framework.BundleActivator#start(org.osgi.framework.BundleContext
* )
*/
public
void
start(BundleContext bundleContext)
throws
Exception {
ClientActivator.context = bundleContext;
HostService.service();
}
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重启OSGI Framework，
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osgi> ss
Framework is launched.
id State Bundle
0
ACTIVE org.eclipse.osgi_3.
6.2
.R36x_v20110210
1
<<LAZY>> org.salever.osgi.depends.hostbundle_1.
0.0
.qualifier
2
<<LAZY>> org.salever.osgi.depends.clientbundle_1.
0.0
.qualifier
osgi> start
2
class
org.salever.osgi.depends.hostbundle.HostService: Service
osgi> ss
Framework is launched.
id State Bundle
0
ACTIVE org.eclipse.osgi_3.
6.2
.R36x_v20110210
1
ACTIVE org.salever.osgi.depends.hostbundle_1.
0.0
.qualifier
2
ACTIVE org.salever.osgi.depends.clientbundle_1.
0.0
.qualifier
osgi>
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这时候，hostbundle也启动了。这个与OSGI的lazy-start机制有关。bundle的lclass或者其它资源被Class loader装载的时候，该bundle才会启动。注意<<LAZY>>和RESOLVED 是2种状态。
测试场景3——强制停止依赖的插件
停止hostbundle：
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osgi> stop
1
osgi> ss
Framework is launched.
id State Bundle
0
ACTIVE org.eclipse.osgi_3.
6.2
.R36x_v20110210
1
RESOLVED org.salever.osgi.depends.hostbundle_1.
0.0
.qualifier
2
ACTIVE org.salever.osgi.depends.clientbundle_1.
0.0
.qualifier
osgi>
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clientbundle依然运行，说明在bundle已经启动以后，停止依赖的bundle，对其无影响。
依次停止2个bundle，然后启动clientbundle，看看结果：
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osgi> stop
2
osgi> ss
Framework is launched.
id State Bundle
0
ACTIVE org.eclipse.osgi_3.
6.2
.R36x_v20110210
1
RESOLVED org.salever.osgi.depends.hostbundle_1.
0.0
.qualifier
2
RESOLVED org.salever.osgi.depends.clientbundle_1.
0.0
.qualifier
osgi> start
2
class
org.salever.osgi.depends.hostbundle.HostService: Service
osgi>
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2个bundle都启动。
修改一下代码，看看如果clientbundle一直调用hostbundle的时候，bundle的行为：
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/*
* (non-Javadoc)
*
* @see
* org.osgi.framework.BundleActivator#start(org.osgi.framework.BundleContext
* )
*/
public
void
start(BundleContext bundleContext)
throws
Exception {
ClientActivator.context = bundleContext;
new
Thread(
new
Runnable() {
@Override
public
void
run() {
while
(
true
) {
HostService.service();
try
{
Thread.sleep(
5000
);
}
catch
(InterruptedException e) {
}
System.out.println(
this
.toString() +
": Sleep 5000ms"
);
}
}
}).start();
}
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这里每隔5s，会发生一次调用：
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osgi> org.salever.osgi.depends.clientbundle.ClientActivator$
1
@1808199
: Sleep 5000ms
class
org.salever.osgi.depends.hostbundle.HostService: Service
org.salever.osgi.depends.clientbundle.ClientActivator$
1
@1808199
: Sleep 5000ms
class
org.salever.osgi.depends.hostbundle.HostService: Service
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然后停止hostbundle：
ss Framework is launched. id State Bundle 0 ACTIVE org.eclipse.osgi_3.6.2.R36x_v20110210 1 RESOLVED org.salever.osgi.depends.hostbundle_1.0.0.qualifier 2 ACTIVE org.salever.osgi.depends.clientbundle_1.0.0.qualifier osgi> org.salever.osgi.depends.clientbundle.ClientActivator$1@1808199: Sleep 5000ms class org.salever.osgi.depends.hostbundle.HostService: Service
试试卸载hostbundle：
osgi> uninstall 1 osgi> ss Framework is launched. id State Bundle 0 ACTIVE org.eclipse.osgi_3.6.2.R36x_v20110210 2 ACTIVE org.salever.osgi.depends.clientbundle_1.0.0.qualifier osgi> org.salever.osgi.depends.clientbundle.ClientActivator$1@763f5d: Sleep 5000ms class org.salever.osgi.depends.hostbundle.HostService: Service org.salever.osgi.depends.clientbundle.ClientActivator$1@763f5d: Sleep 5000ms class org.salever.osgi.depends.hostbundle.HostService: Service org.salever.osgi.depends.clientbundle.ClientActivator$1@763f5d: Sleep 5000ms class org.salever.osgi.depends.hostbundle.HostService: Service
说明，只要bundle启动了，就算依赖的bundle没有了，它也不会受其影响。一个可能的解释为，OSGI Framework缓存了这些bundle资源。
测试场景3——依赖的插件不存在
最后我们看看，依赖的bundle不存在的时候，bundle的行为。
回到New OSGI Framework的页面，去掉org.salever.osgi.depends.hostbundle。
启动环境：
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osgi> !SESSION
2012
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04
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17
:
22
:
06.432
-----------------------------------------------
eclipse.buildId=unknown
java.version=
1.6
.0_17
java.vendor=Sun Microsystems Inc.
BootLoader constants: OS=win32, ARCH=x86, WS=win32, NL=en_US
Command-line arguments: -dev file:E:/workspace/common_ws/.metadata/.plugins/org.eclipse.pde.core/New OSGI/dev.properties -os win32 -ws win32 -arch x86 -consoleLog -console -clean
!ENTRY org.eclipse.osgi
2
0
2012
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17
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:
07.308
!MESSAGE One or more bundles are not resolved because the following root constraints are not resolved:
!SUBENTRY
1
org.eclipse.osgi
2
0
2012
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22
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07.309
!MESSAGE Bundle initial
@reference
:file:E:/workspace/common_ws/org.salever.osgi.depends.clientbundle/ was not resolved.
!SUBENTRY
2
org.salever.osgi.depends.clientbundle
2
0
2012
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07.309
!MESSAGE Missing required bundle org.salever.osgi.depends.hostbundle_1.
0.0
.
!ENTRY org.eclipse.osgi
2
0
2012
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22
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07.311
!MESSAGE The following is a complete list of bundles which are not resolved, see the prior log entry
for
the root cause
if
it exists:
!SUBENTRY
1
org.eclipse.osgi
2
0
2012
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04
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05
17
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22
:
07.311
!MESSAGE Bundle org.salever.osgi.depends.clientbundle_1.
0.0
.qualifier [
1
] was not resolved.
!SUBENTRY
2
org.salever.osgi.depends.clientbundle
2
0
2012
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05
17
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07.312
!MESSAGE Missing required bundle org.salever.osgi.depends.hostbundle_1.
0.0
.
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出现错误信息，尝试列举已有的bundle：
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osgi> ss
Framework is launched.
id State Bundle
0
ACTIVE org.eclipse.osgi_3.
6.2
.R36x_v20110210
1
INSTALLED org.salever.osgi.depends.clientbundle_1.
0.0
.qualifier
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bundle状态为已安装，而没有启动，尝试启动：
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osgi> start
1
org.osgi.framework.BundleException: The bundle
"org.salever.osgi.depends.clientbundle_1.0.0.qualifier [1]"
could not be resolved. Reason: Missing Constraint: Require-Bundle: org.salever.osgi.depends.hostbundle; bundle-version=
"1.0.0"
at org.eclipse.osgi.framework.internal.core.AbstractBundle.getResolverError(AbstractBundle.java:
1317
)
at org.eclipse.osgi.framework.internal.core.AbstractBundle.getResolutionFailureException(AbstractBundle.java:
1301
)
at org.eclipse.osgi.framework.internal.core.BundleHost.startWorker(BundleHost.java:
319
)
at org.eclipse.osgi.framework.internal.core.AbstractBundle.start(AbstractBundle.java:
284
)
at org.eclipse.osgi.framework.internal.core.AbstractBundle.start(AbstractBundle.java:
276
)
at org.eclipse.osgi.framework.internal.core.FrameworkCommandProvider._start(FrameworkCommandProvider.java:
252
)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:
39
)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:
25
)
at java.lang.reflect.Method.invoke(Method.java:
597
)
at org.eclipse.osgi.framework.internal.core.FrameworkCommandInterpreter.execute(FrameworkCommandInterpreter.java:
155
)
at org.eclipse.osgi.framework.internal.core.FrameworkConsole.docommand(FrameworkConsole.java:
156
)
at org.eclipse.osgi.framework.internal.core.FrameworkConsole.runConsole(FrameworkConsole.java:
141
)
at org.eclipse.osgi.framework.internal.core.FrameworkConsole.run(FrameworkConsole.java:
105
)
at java.lang.Thread.run(Thread.java:
619
)
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这里就很好的解释了，为什么我们再运行Eclipse RCP插件时候，出现的一些类似错误的原因了。
总结
- 一般情况下，最好把bundle设为Lazy-start，这样可以节约资源，在必要的情况下，bundle会自动启用
- 如果依赖的bundle停止了，正在运行的bundle不会马上停止，仍然会继续运行