在整個Tomcat系列文章講解之前, 我想說的是雖然整個Tomcat體系比較復(fù)雜, 但是Tomcat中的代碼并不難讀, 只要認真花點功夫, 一定能啃下來.

由于篇幅的原因, 很難把Tomcat所有的知識點都放到同一篇文章中, 我將把Tomcat系列文章分為Tomcat的啟動, Tomcat中各模塊的介紹和Tomcat中的設(shè)計模式三部分, 歡迎閱讀與關(guān)注.

一:通過idea搭建Tomcat源碼閱讀環(huán)境

首先我們到Tomcat的官網(wǎng)(http://tomcat.apache.org/)上下載Tomcat的源碼, 本文分析的Tomcat版本是Tomcat7.0.94.

進入官網(wǎng)后在左邊的目錄中選擇Tomcat7, 然后到頁面末尾的源碼區(qū)進行下載.

下載完成后打開idea, 選擇File->Open->選擇tomcat的源碼目錄

然后到項目配置中設(shè)置JDK和源碼目錄. File->Project Structure->project SDK

設(shè)置完畢后我們便可以開始愉快的源碼閱讀之旅了. (eclipse或其他ide搭建環(huán)境的思路也是差不多的, 可以摸索一下).

二:startup源碼分析

當(dāng)我們初學(xué)tomcat的時候, 肯定先要學(xué)習(xí)怎樣啟動tomcat. 在tomcat的bin目錄下有兩個啟動tomcat的文件, 一個是startup.bat, 它用于windows環(huán)境下啟動tomcat; 另一個是startup.sh, 它用于linux環(huán)境下tomcat的啟動. 兩個文件中的邏輯是一樣的, 我們只分析其中的startup.bat.

下面給出startup.bat的源碼

@echo off

rem Licensed to the Apache Software Foundation (ASF) under one or more

rem contributor license agreements. See the NOTICE file distributed with

rem this work for additional information regarding copyright ownership.

rem The ASF licenses this file to You under the Apache License, Version 2.0

rem (the "License"); you may not use this file except in compliance with

rem the License. You may obtain a copy of the License at

rem

rem http://www.apache.org/licenses/LICENSE-2.0

rem

rem Unless required by applicable law or agreed to in writing, software

rem distributed under the License is distributed on an "AS IS" BASIS,

rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

rem See the License for the specific language governing permissions and

rem limitations under the License.

rem ---------------------------------------------------------------------------

rem Start script for the CATALINA Server

rem ---------------------------------------------------------------------------

setlocal

rem Guess CATALINA_HOME if not defined

set "CURRENT_DIR=%cd%"

if not "%CATALINA_HOME%" == "" goto gotHome

set "CATALINA_HOME=%CURRENT_DIR%"

if exist "%CATALINA_HOME%\bin\catalina.bat" goto okHome

cd ..

set "CATALINA_HOME=%cd%"

cd "%CURRENT_DIR%"

:gotHome

if exist "%CATALINA_HOME%\bin\catalina.bat" goto okHome

echo The CATALINA_HOME environment variable is not defined correctly

echo This environment variable is needed to run this program

goto end

:okHome

set "EXECUTABLE=%CATALINA_HOME%\bin\catalina.bat"

rem Check that target executable exists

if exist "%EXECUTABLE%" goto okExec

echo Cannot find "%EXECUTABLE%"

echo This file is needed to run this program

goto end

:okExec

rem Get remaining unshifted command line arguments and save them in the

set CMD_LINE_ARGS=

:setArgs

if ""%1""=="""" goto doneSetArgs

set CMD_LINE_ARGS=%CMD_LINE_ARGS% %1

shift

goto setArgs

:doneSetArgs

call "%EXECUTABLE%" start %CMD_LINE_ARGS%

:end

.bat文件中@echo是打印指令, 用于控制臺輸出信息, rem是注釋符.

跳過開頭的注釋, 我們來到配置CATALINA_HOME的代碼段, 執(zhí)行startup.bat文件首先會設(shè)置CATALINA_HOME.

set "CURRENT_DIR=%cd%"

if not "%CATALINA_HOME%" == "" goto gotHome

set "CATALINA_HOME=%CURRENT_DIR%"

if exist "%CATALINA_HOME%\bin\catalina.bat" goto okHome

cd ..

set "CATALINA_HOME=%cd%"

cd "%CURRENT_DIR%"

:gotHome

if exist "%CATALINA_HOME%\bin\catalina.bat" goto okHome

echo The CATALINA_HOME environment variable is not defined correctly

echo This environment variable is needed to run this program

goto end

:okHome

先通過set指令把當(dāng)前目錄設(shè)置到一個名為CURRENT_DIR的變量中,

如果系統(tǒng)中配置過CATALINA_HOME則跳到gotHome代碼段. 正常情況下我們的電腦都沒有配置CATALINA_HOME, 所以往下執(zhí)行, 把當(dāng)前目錄設(shè)置為CATALINA_HOME.

然后判斷CATALINA_HOME目錄下是否存在catalina.bat文件, 如果存在就跳到okHome代碼塊.

在okHome中, 會把catalina.bat文件的的路徑賦給一個叫EXECUTABLE的變量, 然后會進一步判斷這個路徑是否存在, 存在則跳轉(zhuǎn)到okExec代碼塊, 不存在的話會在控制臺輸出一些錯誤信息.

在okExec中, 會把setArgs代碼塊的返回結(jié)果賦值給CMD_LINE_ARGS變量, 這個變量用于存儲啟動參數(shù).

setArgs中首先會判斷是否有參數(shù), (if ""%1""==""""判斷第一個參數(shù)是否為空), 如果沒有參數(shù)則相當(dāng)于參數(shù)項為空. 如果有參數(shù)則循環(huán)遍歷所有的參數(shù)(每次拼接第一個參數(shù)).

最后執(zhí)行call "%EXECUTABLE%" start %CMD_LINE_ARGS%, 也就是說執(zhí)行catalina.bat文件, 如果有參數(shù)則帶上參數(shù).

總結(jié): startup.bat文件實際上就做了一件事情: 啟動catalina.bat.

ps: 這樣看來, 在windows下啟動tomcat未必一定要通過startup.bat, 用catalina.bat start也是可以的.

catalina.bat源碼分析

為了不讓文章看起來太臃腫, 這里就不先把整個文件貼出來了, 我們逐塊代碼進行分析.

跳過開頭的注釋, 我們來到下面的代碼段:

setlocal

rem Suppress Terminate batch job on CTRL+C

if not ""%1"" == ""run"" goto mainEntry

if "%TEMP%" == "" goto mainEntry

if exist "%TEMP%\%~nx0.run" goto mainEntry

echo Y>"%TEMP%\%~nx0.run"

if not exist "%TEMP%\%~nx0.run" goto mainEntry

echo Y>"%TEMP%\%~nx0.Y"

call "%~f0" %*

rem Use provided errorlevel

set RETVAL=%ERRORLEVEL%

del /Q "%TEMP%\%~nx0.Y" >NUL 2>&1

exit /B %RETVAL%

:mainEntry

del /Q "%TEMP%\%~nx0.run" >NUL 2>&1

大多情況下我們啟動tomcat都沒有設(shè)置參數(shù), 所以直接跳到mainEntry代碼段, 刪除了一個臨時文件后, 繼續(xù)往下執(zhí)行.

rem Guess CATALINA_HOME if not defined

set "CURRENT_DIR=%cd%"

if not "%CATALINA_HOME%" == "" goto gotHome

set "CATALINA_HOME=%CURRENT_DIR%"

if exist "%CATALINA_HOME%\bin\catalina.bat" goto okHome

cd ..

set "CATALINA_HOME=%cd%"

cd "%CURRENT_DIR%"

:gotHome

if exist "%CATALINA_HOME%\bin\catalina.bat" goto okHome

echo The CATALINA_HOME environment variable is not defined correctly

echo This environment variable is needed to run this program

goto end

:okHome

rem Copy CATALINA_BASE from CATALINA_HOME if not defined

if not "%CATALINA_BASE%" == "" goto gotBase

set "CATALINA_BASE=%CATALINA_HOME%"

可以看到這段代碼與startup.bat中開頭的代碼相似, 在確定CATALINA_HOME下有catalina.bat后把CATALINA_HOME賦給變量CATALINA_BASE.

rem Get standard environment variables

if not exist "%CATALINA_BASE%\bin\setenv.bat" goto checkSetenvHome

call "%CATALINA_BASE%\bin\setenv.bat"

goto setenvDone

:checkSetenvHome

if exist "%CATALINA_HOME%\bin\setenv.bat" call "%CATALINA_HOME%\bin\setenv.bat"

:setenvDone

rem Get standard Java environment variables

if exist "%CATALINA_HOME%\bin\setclasspath.bat" goto okSetclasspath

echo Cannot find "%CATALINA_HOME%\bin\setclasspath.bat"

echo This file is needed to run this program

goto end

:okSetclasspath

call "%CATALINA_HOME%\bin\setclasspath.bat" %1

if errorlevel 1 goto end

rem Add on extra jar file to CLASSPATH

rem Note that there are no quotes as we do not want to introduce random

rem quotes into the CLASSPATH

if "%CLASSPATH%" == "" goto emptyClasspath

set "CLASSPATH=%CLASSPATH%;"

:emptyClasspath

set "CLASSPATH=%CLASSPATH%%CATALINA_HOME%\bin\bootstrap.jar"

上面這段代碼依次執(zhí)行了setenv.bat和setclasspath.bat文件, 目的是獲得CLASSPATH, 相信會Java的同學(xué)應(yīng)該都會在配置環(huán)境變量時都配置過classpath, 系統(tǒng)拿到classpath路徑后把它和CATALINA_HOME拼接在一起, 最終定位到一個叫bootstrap.jar的文件. 雖然后面還有很多代碼, 但是這里必須暫停提示一下: bootstrap.jar將是我們啟動tomcat的環(huán)境.

接下來從gotTmpdir代碼塊到noEndorsedVar代碼塊進行了一些配置, 由于不是主要內(nèi)容暫且跳過.

echo Using CATALINA_BASE: "%CATALINA_BASE%"

echo Using CATALINA_HOME: "%CATALINA_HOME%"

echo Using CATALINA_TMPDIR: "%CATALINA_TMPDIR%"

if ""%1"" == ""debug"" goto use_jdk

echo Using JRE_HOME: "%JRE_HOME%"

goto java_dir_displayed

:use_jdk

echo Using JAVA_HOME: "%JAVA_HOME%"

:java_dir_displayed

echo Using CLASSPATH: "%CLASSPATH%"

set _EXECJAVA=%_RUNJAVA%

set MAINCLASS=org.apache.catalina.startup.Bootstrap

set ACTION=start

set SECURITY_POLICY_FILE=

set DEBUG_OPTS=

set JPDA=

if not ""%1"" == ""jpda"" goto noJpda

set JPDA=jpda

if not "%JPDA_TRANSPORT%" == "" goto gotJpdaTransport

set JPDA_TRANSPORT=dt_socket

:gotJpdaTransport

if not "%JPDA_ADDRESS%" == "" goto gotJpdaAddress

set JPDA_ADDRESS=8000

:gotJpdaAddress

if not "%JPDA_SUSPEND%" == "" goto gotJpdaSuspend

set JPDA_SUSPEND=n

:gotJpdaSuspend

if not "%JPDA_OPTS%" == "" goto gotJpdaOpts

set JPDA_OPTS=-agentlib:jdwp=transport=%JPDA_TRANSPORT%,address=%JPDA_ADDRESS%,server=y,suspend=%JPDA_SUSPEND%

:gotJpdaOpts

shift

:noJpda

if ""%1"" == ""debug"" goto doDebug

if ""%1"" == ""run"" goto doRun

if ""%1"" == ""start"" goto doStart

if ""%1"" == ""stop"" goto doStop

if ""%1"" == ""configtest"" goto doConfigTest

if ""%1"" == ""version"" goto doVersion

接下來, 我們能看到一些重要的信息, 其中的重點是:

set _EXECJAVA=%_RUNJAVA%, 設(shè)置了jdk中bin目錄下的java.exe文件路徑.

set MAINCLASS=org.apache.catalina.startup.Bootstrap, 設(shè)置了tomcat的啟動類為Bootstrap這個類. (后面會分析這個類)

set ACTION=start設(shè)置tomcat啟動

大家可以留意這些參數(shù), 最后執(zhí)行tomcat的啟動時會用到.

if not ""%1"" == ""jpda"" goto noJpda

set JPDA=jpda

if not "%JPDA_TRANSPORT%" == "" goto gotJpdaTransport

set JPDA_TRANSPORT=dt_socket

:gotJpdaTransport

if not "%JPDA_ADDRESS%" == "" goto gotJpdaAddress

set JPDA_ADDRESS=8000

:gotJpdaAddress

if not "%JPDA_SUSPEND%" == "" goto gotJpdaSuspend

set JPDA_SUSPEND=n

:gotJpdaSuspend

if not "%JPDA_OPTS%" == "" goto gotJpdaOpts

set JPDA_OPTS=-agentlib:jdwp=transport=%JPDA_TRANSPORT%,address=%JPDA_ADDRESS%,server=y,suspend=%JPDA_SUSPEND%

:gotJpdaOpts

shift

:noJpda

if ""%1"" == ""debug"" goto doDebug

if ""%1"" == ""run"" goto doRun

if ""%1"" == ""start"" goto doStart

if ""%1"" == ""stop"" goto doStop

if ""%1"" == ""configtest"" goto doConfigTest

if ""%1"" == ""version"" goto doVersion

接著判斷第一個參數(shù)是否是jpda, 是則進行一些設(shè)定. 而正常情況下第一個參數(shù)是start, 所以跳過這段代碼. 接著會判斷第一個參數(shù)的內(nèi)容, 根據(jù)判斷, 我們會跳到doStart代碼段. (有余力的同學(xué)不妨看下debug, run等啟動方式)

:doStart

shift

if "%TITLE%" == "" set TITLE=Tomcat

set _EXECJAVA=start "%TITLE%" %_RUNJAVA%

if not ""%1"" == ""-security"" goto execCmd

shift

echo Using Security Manager

set "SECURITY_POLICY_FILE=%CATALINA_BASE%\conf\catalina.policy"

goto execCmd

可以看到doStart中無非也是設(shè)定一些參數(shù), 最終會跳轉(zhuǎn)到execCmd代碼段

:execCmd

rem Get remaining unshifted command line arguments and save them in the

set CMD_LINE_ARGS=

:setArgs

if ""%1""=="""" goto doneSetArgs

set CMD_LINE_ARGS=%CMD_LINE_ARGS% %1

shift

goto setArgs

:doneSetArgs

可以看到這段代碼也是在拼接參數(shù), 把參數(shù)拼接到一個叫CMD_LINE_ARGS的變量中, 接下來就是catalina最后的一段代碼了.

rem Execute Java with the applicable properties

if not "%JPDA%" == "" goto doJpda

if not "%SECURITY_POLICY_FILE%" == "" goto doSecurity

%_EXECJAVA% %LOGGING_CONFIG% %LOGGING_MANAGER% %JAVA_OPTS% %CATALINA_OPTS% %DEBUG_OPTS% -D%ENDORSED_PROP%="%JAVA_ENDORSED_DIRS%" -classpath "%CLASSPATH%" -Dcatalina.base="%CATALINA_BASE%" -Dcatalina.home="%CATALINA_HOME%" -Djava.io.tmpdir="%CATALINA_TMPDIR%" %MAINCLASS% %CMD_LINE_ARGS% %ACTION%

goto end

:doSecurity

%_EXECJAVA% %LOGGING_CONFIG% %LOGGING_MANAGER% %JAVA_OPTS% %CATALINA_OPTS% %DEBUG_OPTS% -D%ENDORSED_PROP%="%JAVA_ENDORSED_DIRS%" -classpath "%CLASSPATH%" -Djava.security.manager -Djava.security.policy=="%SECURITY_POLICY_FILE%" -Dcatalina.base="%CATALINA_BASE%" -Dcatalina.home="%CATALINA_HOME%" -Djava.io.tmpdir="%CATALINA_TMPDIR%" %MAINCLASS% %CMD_LINE_ARGS% %ACTION%

goto end

:doJpda

if not "%SECURITY_POLICY_FILE%" == "" goto doSecurityJpda

%_EXECJAVA% %LOGGING_CONFIG% %LOGGING_MANAGER% %JAVA_OPTS% %JPDA_OPTS% %CATALINA_OPTS% %DEBUG_OPTS% -D%ENDORSED_PROP%="%JAVA_ENDORSED_DIRS%" -classpath "%CLASSPATH%" -Dcatalina.base="%CATALINA_BASE%" -Dcatalina.home="%CATALINA_HOME%" -Djava.io.tmpdir="%CATALINA_TMPDIR%" %MAINCLASS% %CMD_LINE_ARGS% %ACTION%

goto end

:doSecurityJpda

%_EXECJAVA% %LOGGING_CONFIG% %LOGGING_MANAGER% %JAVA_OPTS% %JPDA_OPTS% %CATALINA_OPTS% %DEBUG_OPTS% -D%ENDORSED_PROP%="%JAVA_ENDORSED_DIRS%" -classpath "%CLASSPATH%" -Djava.security.manager -Djava.security.policy=="%SECURITY_POLICY_FILE%" -Dcatalina.base="%CATALINA_BASE%" -Dcatalina.home="%CATALINA_HOME%" -Djava.io.tmpdir="%CATALINA_TMPDIR%" %MAINCLASS% %CMD_LINE_ARGS% %ACTION%

goto end

:end

跳過前面兩行判斷后, 來到了關(guān)鍵語句:

%_EXECJAVA% %LOGGING_CONFIG% %LOGGING_MANAGER% %JAVA_OPTS% %CATALINA_OPTS% %DEBUG_OPTS% -D%ENDORSED_PROP%="%JAVA_ENDORSED_DIRS%" -classpath "%CLASSPATH%" -Dcatalina.base="%CATALINA_BASE%" -Dcatalina.home="%CATALINA_HOME%" -Djava.io.tmpdir="%CATALINA_TMPDIR%" %MAINCLASS% %CMD_LINE_ARGS% %ACTION%

_EXECJAVA也就是_RUNJAVA, 也就是平時說的java指令, 但在之前的doStart代碼塊中把_EXECJAVA改為了start "%TITLE%" %_RUNJAVA%, 所以系統(tǒng)會另啟一個命令行窗口, 名字叫Tomcat.

在拼接一系列參數(shù)后, 我們會看見%MAINCLASS%, 也就是org.apache.catalina.startup.Bootstrap啟動類, 拼接完啟動參數(shù)后, 最后拼接的是%ACTION%, 也就是start.

總結(jié): catalina.bat最終執(zhí)行了Bootstrap類中的main方法.

ps: 分析完整個catalina.bat我們發(fā)現(xiàn)我們可以通過設(shè)定不同的參數(shù)讓tomcat以不同的方式運行. 在ide中我們是可以選擇debug等模式啟動tomcat的, 也可以為其配置參數(shù), 在catalina.bat中我們看到了啟動tomcat背后的運作流程.

Tomcat啟動流程分析

上面我們從運行startup.bat一路分析來到Bootstrap的啟動, 下面我們先對Tomcat中的組件進行一次總覽. 由于篇幅的原因, tomcat中各個模塊的關(guān)系將留到下一篇文章敘述, 這里先給出一張tomcat中各模塊的關(guān)系圖.

從圖中我們可以看出tomcat中模塊還是挺多的, 那么tomcat是如何啟動這些模塊的呢? 請看下面這張示意圖.

由圖中我們可以看到從Bootstrap類的main方法開始, tomcat會以鏈的方式逐級調(diào)用各個模塊的init()方法進行初始化, 待各個模塊都初始化后, 又會逐級調(diào)用各個模塊的start()方法啟動各個模塊. 下面我們通過部分源碼看一下這個過程.

首先我們來到Bootstrap類的main方法

public static void main(String args[]) {

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;

}

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);

}

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();

} else if (command.equals("start")) {

daemon.setAwait(true);

daemon.load(args);

daemon.start();

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

// 省略

System.exit(1);

}

}

我們可以看到, Bootstrap類首先會創(chuàng)建一個本類對象, 然后調(diào)用init()方法進行初始化. 執(zhí)行完init()方法后會判斷啟動參數(shù)的值, 由于我們采取默認的啟動方式, 所以main方法的參數(shù)是start, 會進入下面的判斷代碼塊

else if (command.equals("start")) {

daemon.setAwait(true);

daemon.load(args);

daemon.start();

if (null == daemon.getServer()) {

System.exit(1);

}

可以看到在設(shè)置等待后, 調(diào)用了本類對象的load()方法. 我們跟進查看load()方法的源碼.

private void load(String[] arguments)

throws Exception {

// Call the load() method

String methodName = "load";

Object param[];

Class> paramTypes[];

if (arguments==null || arguments.length==0) {

paramTypes = null;

param = null;

} else {

paramTypes = new Class[1];

paramTypes[0] = arguments.getClass();

param = new Object[1];

param[0] = arguments;

}

Method method =

catalinaDaemon.getClass().getMethod(methodName, paramTypes);

if (log.isDebugEnabled())

log.debug("Calling startup class " + method);

method.invoke(catalinaDaemon, param);

}

可以看到方法的最后通過反射的方式調(diào)用了成員變量catalinaDaemon的load()方法. 通過跟蹤源碼我們可以看到catalinaDaemon是Bootstrap類的一個私有成員變量

/**

* Daemon reference.

*/

private Object catalinaDaemon = null;

它會在Bootstrap的init()方法中通過反射的方式完成初始化. 下面我們回過頭來看init()方法的源碼.

public void init()

throws Exception

{

// Set Catalina path

setCatalinaHome();

setCatalinaBase();

initClassLoaders();

Thread.currentThread().setContextClassLoader(catalinaLoader);

SecurityClassLoad.securityClassLoad(catalinaLoader);

// Load our startup class and call its process() method

if (log.isDebugEnabled())

log.debug("Loading startup class");

Class> startupClass =

catalinaLoader.loadClass

("org.apache.catalina.startup.Catalina");

Object startupInstance = startupClass.newInstance();

// Set the shared extensions class loader

if (log.isDebugEnabled())

log.debug("Setting startup class properties");

String methodName = "setParentClassLoader";

Class> paramTypes[] = new Class[1];

paramTypes[0] = Class.forName("java.lang.ClassLoader");

Object paramValues[] = new Object[1];

paramValues[0] = sharedLoader;

Method method =

startupInstance.getClass().getMethod(methodName, paramTypes);

method.invoke(startupInstance, paramValues);

catalinaDaemon = startupInstance;

}

可以看到init()方法創(chuàng)建了一個Catalina對象, 并把該對象賦給了catalinaDaemon.

再回過頭來看之前分享給大家的啟動流程圖, 對應(yīng)的是這一塊

后面的過程我就不逐一分析了, 你可以按照這張圖去跟蹤代碼進行驗證. 最終所有模塊都能被初始化并啟動.

本篇結(jié)束

看到這里相信你應(yīng)該對tomcat的啟動過程已經(jīng)有一個清晰的認識了, 但是這僅僅是理解tomcat的開始, 下一篇文章開始我將會詳細介紹tomcat中的組件, 以及組件間的關(guān)系. 了解了各個組件后, tomcat的結(jié)構(gòu)于你而言將不再神秘.

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