tomcat架構

從這張圖上, 可以很明確的看出, 各個元件的關係

Server: 伺服器, 也就是一個tomcat

Service: 服務, 將多個 Connector 和 一個 Engine 組合起來, 成為一個服務. 1#Server -- n#Service

Connector: 接收器, 用於接收指定協議下的連線, 並交給唯一的 Engine 處理

Engine: 引擎, 用於處理連線的執行器, 預設的引擎name=catalina. 1#Service -- 1#Engine

Host: 基於域名匹配至指定虛擬機器. 預設是 localhost , 也可以設定別的, 如 www.xyz.com . 1#Engine -- n#Host

Context: 應用, 其實就是 webapps 下的資料夾. 部署的1個war包, 解壓出來就是一個Context. 1#Host -- n#Context

Wrapper: Servlet. 圖上沒有體現. 他是對Servlet的封裝. 1#Context -- n#Wrapper

將上面的對應關係連起來, 就是:

conf/server.xml

server.xml關係到整個服務的結構和內容.

<?xml version="1.0" encoding="UTF-8"?>
<Server port="8005" shutdown="SHUTDOWN">
  <
 
Listener className="org.apache.catalina.startup.VersionLoggerListener" />
  <!--APR library loader. Documentation at /docs/apr.html -->
  <Listener className="org.apache.catalina.core.AprLifecycleListener" SSLEngine="on" />
  <!-- Prevent memory leaks due to use of particular java/javax APIs
 
-->
  <Listener className="org.apache.catalina.core.JreMemoryLeakPreventionListener" />
  <Listener className="org.apache.catalina.mbeans.GlobalResourcesLifecycleListener" />
  <Listener className="org.apache.catalina.core.ThreadLocalLeakPreventionListener" />

  <!-- Global JNDI resources
       Documentation at /docs/jndi-resources-howto.html
  -->
  <GlobalNamingResources>
    <!-- Editable user database that can also be used by
         UserDatabaseRealm to authenticate users
    -->
    <Resource name="UserDatabase" auth="Container"
              type="org.apache.catalina.UserDatabase"
              description="User database that can be updated and saved"
              factory="org.apache.catalina.users.MemoryUserDatabaseFactory"
              pathname="conf/tomcat-users.xml" />
  </GlobalNamingResources>

  <Service name="Catalina">

    <!--The connectors can use a shared executor, you can define one or more named thread pools-->
    <!--
    <Executor name="tomcatThreadPool" namePrefix="catalina-exec-"
        maxThreads="150" minSpareThreads="4"/>
    -->


    <!-- A "Connector" represents an endpoint by which requests are received
         and responses are returned. Documentation at :
         Java HTTP Connector: /docs/config/http.html
         Java AJP  Connector: /docs/config/ajp.html
         APR (HTTP/AJP) Connector: /docs/apr.html
         Define a non-SSL/TLS HTTP/1.1 Connector on port 8080
    -->
    <Connector port="8080" protocol="HTTP/1.1"
               connectionTimeout="20000"
               redirectPort="8443" />
    <!-- A "Connector" using the shared thread pool-->
    <!--
    <Connector executor="tomcatThreadPool"
               port="8080" protocol="HTTP/1.1"
               connectionTimeout="20000"
               redirectPort="8443" />
    -->
    <!-- Define an SSL/TLS HTTP/1.1 Connector on port 8443
         This connector uses the NIO implementation. The default
         SSLImplementation will depend on the presence of the APR/native
         library and the useOpenSSL attribute of the
         AprLifecycleListener.
         Either JSSE or OpenSSL style configuration may be used regardless of
         the SSLImplementation selected. JSSE style configuration is used below.
    -->
    <!--
    <Connector port="8443" protocol="org.apache.coyote.http11.Http11NioProtocol"
               maxThreads="150" SSLEnabled="true">
        <SSLHostConfig>
            <Certificate certificateKeystoreFile="conf/localhost-rsa.jks"
                         type="RSA" />
        </SSLHostConfig>
    </Connector>
    -->
    <!-- Define an SSL/TLS HTTP/1.1 Connector on port 8443 with HTTP/2
         This connector uses the APR/native implementation which always uses
         OpenSSL for TLS.
         Either JSSE or OpenSSL style configuration may be used. OpenSSL style
         configuration is used below.
    -->
    <!--
    <Connector port="8443" protocol="org.apache.coyote.http11.Http11AprProtocol"
               maxThreads="150" SSLEnabled="true" >
        <UpgradeProtocol className="org.apache.coyote.http2.Http2Protocol" />
        <SSLHostConfig>
            <Certificate certificateKeyFile="conf/localhost-rsa-key.pem"
                         certificateFile="conf/localhost-rsa-cert.pem"
                         certificateChainFile="conf/localhost-rsa-chain.pem"
                         type="RSA" />
        </SSLHostConfig>
    </Connector>
    -->

    <!-- Define an AJP 1.3 Connector on port 8009 -->
    <!--
    <Connector protocol="AJP/1.3"
               address="::1"
               port="8009"
               redirectPort="8443" />
    -->

    <!-- An Engine represents the entry point (within Catalina) that processes
         every request.  The Engine implementation for Tomcat stand alone
         analyzes the HTTP headers included with the request, and passes them
         on to the appropriate Host (virtual host).
         Documentation at /docs/config/engine.html -->

    <!-- You should set jvmRoute to support load-balancing via AJP ie :
    <Engine name="Catalina" defaultHost="localhost" jvmRoute="jvm1">
    -->
    <Engine name="Catalina" defaultHost="localhost">

      <!--For clustering, please take a look at documentation at:
          /docs/cluster-howto.html  (simple how to)
          /docs/config/cluster.html (reference documentation) -->
      <!--
      <Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster"/>
      -->

      <!-- Use the LockOutRealm to prevent attempts to guess user passwords
           via a brute-force attack -->
      <Realm className="org.apache.catalina.realm.LockOutRealm">
        <!-- This Realm uses the UserDatabase configured in the global JNDI
             resources under the key "UserDatabase".  Any edits
             that are performed against this UserDatabase are immediately
             available for use by the Realm.  -->
        <Realm className="org.apache.catalina.realm.UserDatabaseRealm"
               resourceName="UserDatabase"/>
      </Realm>

      <Host name="localhost"  appBase="webapps"
            unpackWARs="true" autoDeploy="true">

        <!-- SingleSignOn valve, share authentication between web applications
             Documentation at: /docs/config/valve.html -->
        <!--
        <Valve className="org.apache.catalina.authenticator.SingleSignOn" />
        -->

        <!-- Access log processes all example.
             Documentation at: /docs/config/valve.html
             Note: The pattern used is equivalent to using pattern="common" -->
        <Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs"
               prefix="localhost_access_log" suffix=".txt"
               pattern="%h %l %u %t &quot;%r&quot; %s %b" />

      </Host>
    </Engine>
  </Service>
</Server>

除錯設定

1. 在除錯程式碼的時候, 可以通過一些配置, 將catalina-home獨立出來. 當然, 不設定也沒有關係.

VM options: 
-Dfile.encoding=UTF-8
-Dcatalina.home=catalina-home
-Dcatalina.base=catalina-home
-Djava.endorsed.dirs=catalina-home/endorsed
-Djava.io.tmpdir=catalina-home/temp
-Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager
-Djava.util.logging.config.file=catalina-home/conf/logging.properties

然後將conf, webapps拷貝過來

2. 除錯執行的時候, 會報錯, 此時在org.apache.catalina.startup.ContextConfig#configureStart()中加一句程式碼:

context.addServletContainerInitializer(new JasperInitializer(), null);

Bootstrap

tomcat入口程式, 跟很多別的程式類似, 入口程式是 Bootstrap, 中文直譯過來, Bootstrap --> 引導.

/**
 * tomcat入口方法 
 * Main method and entry point when starting Tomcat via the provided
 * scripts.
 *
 * @param args Command line arguments to be processed
 */
public static void main(String args[]) {

    // 建立 + 初始化
    synchronized (daemonLock) {
        if (daemon == null) {
            // Don't set daemon until init() has completed
            Bootstrap bootstrap = new Bootstrap();
            try {
                bootstrap.init();
            } catch (Throwable t) {
                handleThrowable(t);
                t.printStackTrace();
                return;
            }
            // 賦值給守護變數
            daemon = bootstrap;
        } else {
            // When running as a service the call to stop will be on a new
            // thread so make sure the correct class loader is used to
            // prevent a range of class not found exceptions.
            Thread.currentThread().setContextClassLoader(daemon.catalinaLoader);
        }
    }

    // 命令檢測, 預設為 start
    try {
        String command = "start";
        if (args.length > 0) {
            command = args[args.length - 1];
        }

        if (command.equals("startd")) {
            args[args.length - 1] = "start";
            daemon.load(args);
            daemon.start();
        } else if (command.equals("stopd")) {
            args[args.length - 1] = "stop";
            daemon.stop();
        }
        // 預設情況下走這裡
        else if (command.equals("start")) {
            daemon.setAwait(true);
            daemon.load(args);
            daemon.start();
            // server沒起來, 則退出
            if (null == daemon.getServer()) {
                System.exit(1);
            }
        } else if (command.equals("stop")) {
            daemon.stopServer(args);
        } else if (command.equals("configtest")) {
            daemon.load(args);
            if (null == daemon.getServer()) {
                System.exit(1);
            }
            System.exit(0);
        } else {
            log.warn("Bootstrap: command \"" + command + "\" does not exist.");
        }
    } catch (Throwable t) {
        // Unwrap the Exception for clearer error reporting
        if (t instanceof InvocationTargetException && t.getCause() != null) {
            t = t.getCause();
        }
        handleThrowable(t);
        t.printStackTrace();
        System.exit(1);
    }
}

main方法主要呼叫了三個方法:

1. init

2. load

3. start

從名字上猜測, 應該是 先初始化, 然後載入一些資源, 最後啟動整個服務.