Jetty 是一个轻量级的、开源的servlet容器,可以非常容易的嵌入到应用程序当中作为嵌入式服务器使用,下面我们从代码层面来看看它是如何启动的
Jetty的启动从Server类的start()方法开始的,Server类继承了AbstractLifeCycle类,会首先执行AbstractLifeCycle的start()方法.方法如下:
public final void start() throws Exception
{
synchronized (_lock)
{
try
{
if (_state == STARTED || _state == STARTING)
return;
setStarting();//启动之前调用监听器
doStart();//启动jetty
Log.debug("started {}",this);
setStarted();//启动之后调用监听器
}
catch (Exception e)
{
setFailed(e);
throw e;
}
catch (Error e)
{
setFailed(e);
throw e;
}
}
}
doStart()方法在Server类中.如下:
/* ------------------------------------------------------------ */
protected void doStart() throws Exception
{
Log.info("jetty-"+_version);
HttpGenerator.setServerVersion(_version);
MultiException mex=new MultiException();
for (int i=0;_realms !=null && i<_realms.length; i++)
{
if (_realms[i] instanceof LifeCycle)
((LifeCycle)_realms[i]).start();
}
Iterator itor = _dependentLifeCycles.iterator();
while (itor.hasNext())
{
try
{
((LifeCycle)itor.next()).start();
}
catch (Throwable e) {mex.add(e);}
}
if (_threadPool==null)
{
QueuedThreadPool tp=new QueuedThreadPool();
setThreadPool(tp);
}
if (_sessionIdManager!=null)
_sessionIdManager.start();
try
{
if (_threadPool instanceof LifeCycle)
((LifeCycle)_threadPool).start();
}
catch(Throwable e) { mex.add(e);}
try
{
super.doStart();
}
catch(Throwable e)
{
Log.warn("Error starting handlers",e);
}
if (_connectors!=null)
{
for (int i=0;i<_connectors.length;i++)
{
try{_connectors[i].start();}
catch(Throwable e)
{
mex.add(e);
}
}
}
mex.ifExceptionThrow();
}
这里面启动了处理请求的线程和Session管理器,还有连接器,super.doStart()调用了HandlerWrapper类的doStart()方法,如下:
protected void doStart() throws Exception
{
if (_handler!=null)
_handler.start();
super.doStart();
}
_handler.start()调用了AbstractLifeCycle的start()方法,同上面,AbstractLifeCycle里面的start()方法会调用
WebAppContext的doStart()方法,如下:
protected void doStart() throws Exception
{
try
{
// 初始化四个类WebInfConfiguration,WebXmlConfiguration, JettyWebXmlConfiguration,TagLibConfiguration
loadConfigurations();
for (int i=0;i<_configurations.length;i++)
_configurations[i].setWebAppContext(this);
// Configure classloader
_ownClassLoader=false;
if (getClassLoader()==null)
{
WebAppClassLoader classLoader = new WebAppClassLoader(this);
setClassLoader(classLoader);//生成classloader加载应用的war
_ownClassLoader=true;
}
if (Log.isDebugEnabled())//打印日志
{
ClassLoader loader = getClassLoader();
Log.debug("Thread Context class loader is: " + loader);
loader=loader.getParent();
while(loader!=null)
{
Log.debug("Parent class loader is: " + loader);
loader=loader.getParent();
}
}
for (int i=0;i<_configurations.length;i++)
_configurations[i].configureClassLoader();//WebInfConfiguration类加载war包的lib,classes目录
getTempDirectory();
if (_tmpDir!=null && !_isExistingTmpDir && !isTempWorkDirectory())
{
File sentinel = new File(_tmpDir, ".active");
if(!sentinel.exists())
sentinel.mkdir();
}
super.doStart();
if (isLogUrlOnStart())
dumpUrl();
}
catch (Exception e)
{
//start up of the webapp context failed, make sure it is not started
Log.warn("Failed startup of context "+this, e);
_unavailableException=e;
_unavailable = true;
}
}
WebInfConfiguration类的configureClassLoader()方法如下:
public void configureClassLoader()
throws Exception
{
//cannot configure if the context is already started
if (_context.isStarted())
{
if (Log.isDebugEnabled()){Log.debug("Cannot configure webapp after it is started");}
return;
}
Resource web_inf=_context.getWebInf();//生成临时目录将war拷过来
// Add WEB-INF classes and lib classpaths
if (web_inf != null && web_inf.isDirectory() && _context.getClassLoader() instanceof WebAppClassLoader)
{
// Look for classes directory
Resource classes= web_inf.addPath("classes/");
if (classes.exists())
((WebAppClassLoader)_context.getClassLoader()).addClassPath(classes.toString());
// Look for jars
Resource lib= web_inf.addPath("lib/");
if (lib.exists() || lib.isDirectory())
((WebAppClassLoader)_context.getClassLoader()).addJars(lib);
}
}
WebAppContext的start()方法里的 super.doStart()会调用ContextHandler的doStart()方法,方法如下:
protected void doStart() throws Exception
{
if (_contextPath==null)
throw new IllegalStateException("Null contextPath");
_logger=Log.getLogger(getDisplayName()==null?getContextPath():getDisplayName());
ClassLoader old_classloader=null;
Thread current_thread=null;
SContext old_context=null;
_contextAttributes=new AttributesMap();
try
{
// Set the classloader
if (_classLoader!=null)
{
current_thread=Thread.currentThread();
old_classloader=current_thread.getContextClassLoader();
current_thread.setContextClassLoader(_classLoader);
}
if (_mimeTypes==null)
_mimeTypes=new MimeTypes();
old_context=(SContext)__context.get();
__context.set(_scontext);
if (_errorHandler==null)
setErrorHandler(new ErrorHandler());
startContext();
}
finally
{
__context.set(old_context);
// reset the classloader
if (_classLoader!=null)
{
current_thread.setContextClassLoader(old_classloader);
}
}
}
startContext()方法会调用WebAppContext类的startContext()方法,如下:
protected void startContext()
throws Exception
{
// Configure defaults
for (int i=0;i<_configurations.length;i++)
_configurations[i].configureDefaults();//调用WebXmlConfiguration类解析xml文件
// Is there a WEB-INF work directory
Resource web_inf=getWebInf();
if (web_inf!=null)
{
Resource work= web_inf.addPath("work");
if (work.exists()
&& work.isDirectory()
&& work.getFile() != null
&& work.getFile().canWrite()
&& getAttribute(ServletHandler.__J_S_CONTEXT_TEMPDIR) == null)
setAttribute(ServletHandler.__J_S_CONTEXT_TEMPDIR, work.getFile());
}
// Configure webapp
for (int i=0;i<_configurations.length;i++)
_configurations[i].configureWebApp();
super.startContext();
}
super.startContext()调用父类Context的startContext()方法,如下:
protected void startContext() throws Exception
{
super.startContext();//初始化xml里配置的listener
// OK to Initialize servlet handler now
if (_servletHandler != null && _servletHandler.isStarted())
_servletHandler.initialize();//初始化xml里面配置的servlet
}