Table of contents
2. The default implementation of each component
One: Process
steps :
1
) To start
tomcat
, you need to call
bin/startup.bat (
in
the linux
directory
,
you need to call
bin/startup.sh), and in the startup.bat
script
,
call
catalina.bat
.
2
) In the
catalina.bat script file,
the main method in BootStrap
is called
.
3
)
The init method is called in the main method of
BootStrap
to create Catalina and initialize the class loader.
4
)
The load method is called in the main method of
BootStrap , and
the load method of Catalina is called in it .
5
) In
the load method of
Catalina
, some initialization work is required , and a Digester object needs to be constructed , using
for parsing
XML
.
6
) Then call the initialization operation of subsequent components. . . Load the Tomcat
configuration file, initialize the container component, listen to the corresponding port number, and prepare to accept client requests.
Two: source code analysis
1.Lifecycle
Since all components have life cycle methods such as initialization, start, and stop, they have the characteristics of life cycle management.
Therefore, when
Tomcat
is designed, it abstracts an interface
Lifecycle based on life cycle management
, and the components Server
,
Service
,
Container
,
Executor
, and
Connector
all implement a life cycle interface, thus having the following life cycle Core method:
1
)
init
(): Initialize the component
2
)
start
(): start the component
3
)
stop
(): stop component
4
)
destroy
(): Destroy the component
2. The default implementation of each component
The Server
,
Service
,
Engine
,
Host
, and
Context
we mentioned above
are all interfaces, and the default implementation classes of these interfaces are listed in the figure below. Currently, for the Endpoint
component,
there is no corresponding Endpoint interface in
Tomcat
, but there is an abstract class AbstractEndpoint , under which there are three implementation classes: NioEndpoint , Nio2Endpoint, AprEndpoint , these three implementation classes correspond to the previously explained linker Coyote When mentioning the three IO models supported by the linker , NIO , NIO2 , APR , and Tomcat8.5 , the default is NioEndpoint .
ProtocolHandler
:
Coyote
protocol interface, by encapsulating
Endpoint
and
Processor
, it realizes the processing function for specific protocols. Tomcat
provides 6 implementation classes
according to the protocol and
IO .
AJP agreement:
1
)
AjpNioProtocol
: adopts the
IO model of
NIO
.
2
)
AjpNio2Protocol
: adopts the
IO model of
NIO2
.
3
)
AjpAprProtocol
:
The IO model using
APR
needs to depend on the APR library.
HTTP protocol:
1
)
Http11NioProtocol
: Adopt the
IO model of
NIO
, the protocol used by default (if the server does not have APR installed).
2
)
Http11Nio2Protocol
: adopts the
IO model of
NIO2
.
3
)
Http11AprProtocol
:
The IO model using
APR
needs to depend on the APR library.
3. Source code entry
Directory: org.apache.catalina.startupMainClass ： BootStrap ‐‐‐‐> main(String[] args)
Three: Summary
From the startup flowchart and the source code, we can see that
the startup process of
Tomcat is very standardized, and
it starts uniformly according to the definition of the lifecycle management interface Lifecycle. First call the init() method to initialize the components step by step, and then call the start() method to start.
In addition to completing its own processing, components at each level are also responsible for invoking the lifecycle management methods of subcomponent responses. Components are loosely coupled because we can easily modify and replace them through configuration files.