本文接下来会介绍Host容器和Engine容器,在tomcat的实际部署中,总是会使用一个Host容器;本文介绍Host接口和Engine接口及其相关类

Host容器是org.apache.catalina.Host接口的实例,Host接口继承自Container接口, 其定义如下



public interface Host extends Container {

public static final String ADD_ALIAS_EVENT = "addAlias";

public static final String REMOVE_ALIAS_EVENT = "removeAlias";

public String getAppBase();

public void setAppBase(String appBase);

public boolean getAutoDeploy();

public void setAutoDeploy(boolean autoDeploy);

public void addDefaultContext(DefaultContext defaultContext);

public DefaultContext getDefaultContext();

public String getName();

public void setName(String name);

public void importDefaultContext(Context context);

public void addAlias(String alias);

public String[] findAliases();

public Context map(String uri);

public void removeAlias(String alias);

}


该接口中比较重要的方法是map()方法,该方法返回一个用来处理引入的HTTP请求的Context容器的实例,该方法的具体实现在StandardHost类中

在tomcat中org.apache.catalina.core.StandardHost类是Host接口的标准实现,该类继承自org.apache.catalina.core.ContainerBase类,实现了Host和Deployer接口

与StandardContext类和StandardWrapper类相似,StandardHost类的构造函数会将一个基础阀的实例添加到其管道对象中:



public StandardHost() {

super();
pipeline.setBasic(new StandardHostValve());

}


基础阀是org.apache.catalina.core.StandardHostValve类的实例

当调用其start()方法时,StandardHost实例会添加两个阀,分别为ErrorReportValve类和ErrorDispatcherValve类的实例,这两个阀均位于org.apache.catalina.valves包下



public synchronized void start() throws LifecycleException {
// Set error report valve
if ((errorReportValveClass != null)
&& (!errorReportValveClass.equals(""))) {
try {
Valve valve = (Valve) Class.forName(errorReportValveClass)
.newInstance();
addValve(valve);
} catch (Throwable t) {
log(sm.getString
("standardHost.invalidErrorReportValveClass",
errorReportValveClass));
}
}

// Set dispatcher valve
addValve(new ErrorDispatcherValve());

super.start();

}


每当引入一个HTTP请求,都会调用Host实例的invoke()方法,这里是StandardHost的父类ContainerBase类的invoke()方法,而ContainerBase类的invoke()方法会调用StandardHost实例的基础阀StandardHostValve实例的invoke()方法;StandardHostValve类的invoke()方法会调用StandardHost类的map()方法来获取相应的Context实例来处理HTTP请求



public Context map(String uri) {

if (debug > 0)
log("Mapping request URI '" + uri + "'");
if (uri == null)
return (null);

// Match on the longest possible context path prefix
if (debug > 1)
log(" Trying the longest context path prefix");
Context context = null;
String mapuri = uri;
while (true) {
context = (Context) findChild(mapuri);
if (context != null)
break;
int slash = mapuri.lastIndexOf('/');
if (slash < 0)
break;
mapuri = mapuri.substring(0, slash);
}

// If no Context matches, select the default Context
if (context == null) {
if (debug > 1)
log(" Trying the default context");
context = (Context) findChild("");
}

// Complain if no Context has been selected
if (context == null) {
log(sm.getString("standardHost.mappingError", uri));
return (null);
}

// Return the mapped Context (if any)
if (debug > 0)
log(" Mapped to context '" + context.getPath() + "'");
return (context);

}


在tomcat4中, StandardHost的父类ContainerBase类会调用其addDefaultMapper()方法创建一个默认映射器,默认映射器的类型由mapperClass属性的值决定



protected void addDefaultMapper(String mapperClass) {

// Do we need a default Mapper?
if (mapperClass == null)
return;
if (mappers.size() >= 1)
return;

// Instantiate and add a default Mapper
try {
Class clazz = Class.forName(mapperClass);
Mapper mapper = (Mapper) clazz.newInstance();
mapper.setProtocol("http");
addMapper(mapper);
} catch (Exception e) {
log(sm.getString("containerBase.addDefaultMapper", mapperClass),
e);
}

}


变量mapperClass的值定义在StandardHst类中

private String mapperClass =

        "org.apache.catalina.core.StandardHostMapper";

在tomcat4中,StandardHost类的start()方法会在方法末尾调用addDefaultMapper()方法,确保默认映射器的创建完成

当然,StandardHostMapper类中最重要的方法是map()方法,下面是map()方法的实现



public Container map(Request request, boolean update) {
// Has this request already been mapped?
if (update && (request.getContext() != null))
return (request.getContext());

// Perform mapping on our request URI
String uri = ((HttpRequest) request).getDecodedRequestURI();
Context context = host.map(uri);

// Update the request (if requested) and return the selected Context
if (update) {
request.setContext(context);
if (context != null)
((HttpRequest) request).setContextPath(context.getPath());
else
((HttpRequest) request).setContextPath(null);
}
return (context);

}


注意,这里map()方法仅仅是简单地调用了Host实例的map()方法

org.apache.catalina.core.StandardHostValve类是StandardHost实例的基础阀,当有引入的HTTP请求时,会调用StandardHostValve类的invoke()方法对其进行处理



public void invoke(Request request, Response response,
ValveContext valveContext)
throws IOException, ServletException {

// Validate the request and response object types
if (!(request.getRequest() instanceof HttpServletRequest) ||
!(response.getResponse() instanceof HttpServletResponse)) {
return; // NOTE - Not much else we can do generically
}

// Select the Context to be used for this Request
StandardHost host = (StandardHost) getContainer();
Context context = (Context) host.map(request, true);
if (context == null) {
((HttpServletResponse) response.getResponse()).sendError
(HttpServletResponse.SC_INTERNAL_SERVER_ERROR,
sm.getString("standardHost.noContext"));
return;
}

// Bind the context CL to the current thread
Thread.currentThread().setContextClassLoader
(context.getLoader().getClassLoader());

// Update the session last access time for our session (if any)
HttpServletRequest hreq = (HttpServletRequest) request.getRequest();
String sessionId = hreq.getRequestedSessionId();
if (sessionId != null) {
Manager manager = context.getManager();
if (manager != null) {
Session session = manager.findSession(sessionId);
if ((session != null) && session.isValid())
session.access();
}
}

// Ask this Context to process this request
context.invoke(request, response);

}


在tomcat4中,invoke()方法会调用StandardHost实例的map()方法获取一个相应的Context实例;然后获取与该request对象相关联的session对象,并调用其access()方法,access()方法会修改session对象的最后访问时间;最后调用Context实例的invoke()来处理HTTP请求

接下来描述Engine容器,Engine容器是org.apache.catalina.Engine接口的实例,Engine容器也就是Tomcat的servlet引擎



public interface Engine extends Container {

public String getDefaultHost();

public void setDefaultHost(String defaultHost);

public String getJvmRoute();

public void setJvmRoute(String jvmRouteId);

public Service getService();

public void setService(Service service);

public void addDefaultContext(DefaultContext defaultContext);

public DefaultContext getDefaultContext();

public void importDefaultContext(Context context);

}


在Engine容器中,可以设置一个默认的Host容器或一个默认的Context容器,注意,Engine容器可以与一个服务实例相关联

org.apache.catalina.core.StandardEngine类是Engine接口的标准实现,在实例化的时候,StandardEngine类会添加一个基础阀



public StandardEngine() {

super();
pipeline.setBasic(new StandardEngineValve());

}


org.apache.catalina.core.StandardEngineValve类是StandardEngine容器的基础阀,下面是它的invoke()方法的实现代码



public void invoke(Request request, Response response,
ValveContext valveContext)
throws IOException, ServletException {
// Validate the request and response object types
if (!(request.getRequest() instanceof HttpServletRequest) ||
!(response.getResponse() instanceof HttpServletResponse)) {
return; // NOTE - Not much else we can do generically
}

// Validate that any HTTP/1.1 request included a host header
HttpServletRequest hrequest = (HttpServletRequest) request;
if ("HTTP/1.1".equals(hrequest.getProtocol()) &&
(hrequest.getServerName() == null)) {
((HttpServletResponse) response.getResponse()).sendError
(HttpServletResponse.SC_BAD_REQUEST,
sm.getString("standardEngine.noHostHeader",
request.getRequest().getServerName()));
return;
}

// Select the Host to be used for this Request
StandardEngine engine = (StandardEngine) getContainer();
Host host = (Host) engine.map(request, true);
if (host == null) {
((HttpServletResponse) response.getResponse()).sendError
(HttpServletResponse.SC_BAD_REQUEST,
sm.getString("standardEngine.noHost",
request.getRequest().getServerName()));
return;
}

// Ask this Host to process this request
host.invoke(request, response);

}


在验证了request和response对象的类型后,invoke()方法会通过调用Engine实例的map()方法获取Host对象;得到Host对象以后,调用其invoke()方法处理请求