代碼片段:

org.apache.catalina.startup.Bootstrap#main()

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;
}

Bootstrap static {}

Bootstrap有一個靜態代碼塊, 用來獲取tomcat的作業目錄和安裝目錄.

默認情況下, 是作業目錄和安裝目錄是相同的, 也可以配置成不同的.

// 這里有一個靜態代碼塊
static {
    // Will always be non-null
    // 獲取用戶目錄
    String userDir = System.getProperty("user.dir");

    // Home first
    // tomcat的安裝目錄
    String home = System.getProperty(Constants.CATALINA_HOME_PROP);

    File homeFile = null;

    if (home != null) {
        File f = new File(home);
        try {
            homeFile = f.getCanonicalFile();
        } catch (IOException ioe) {
            homeFile = f.getAbsoluteFile();
        }
    }

    if (homeFile == null) {
        // First fall-back. See if current directory is a bin directory
        // in a normal Tomcat install
        File bootstrapJar = new File(userDir, "bootstrap.jar");

        if (bootstrapJar.exists()) {
            File f = new File(userDir, "..");
            try {
                homeFile = f.getCanonicalFile();
            } catch (IOException ioe) {
                homeFile = f.getAbsoluteFile();
            }
        }
    }

    if (homeFile == null) {
        // Second fall-back. Use current directory
        File f = new File(userDir);
        try {
            homeFile = f.getCanonicalFile();
        } catch (IOException ioe) {
            homeFile = f.getAbsoluteFile();
        }
    }

    catalinaHomeFile = homeFile;
    System.setProperty(Constants.CATALINA_HOME_PROP, catalinaHomeFile.getPath());

    // Then base
    String base = System.getProperty(Constants.CATALINA_BASE_PROP);
    if (base == null) {
        // 一般情況下, 作業目錄 = 安裝目錄
        catalinaBaseFile = catalinaHomeFile;
    } else {
        File baseFile = new File(base);
        try {
            baseFile = baseFile.getCanonicalFile();
        } catch (IOException ioe) {
            baseFile = baseFile.getAbsoluteFile();
        }
        catalinaBaseFile = baseFile;
    }
    System.setProperty(Constants.CATALINA_BASE_PROP, catalinaBaseFile.getPath());
}

bootstrap.init()

public void init() throws Exception {

    // 創建了三個自己的類加載器
    // commonLoader catalinaLoader sharedLoader
    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");

    // 反射加載類: Catalina
    Class<?> startupClass = catalinaLoader.loadClass("org.apache.catalina.startup.Catalina");
    // 反射創建 Catalina
    Object startupInstance = startupClass.getConstructor().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);

    // 呼叫 Catalina#setParentClassLoader(sharedLoader), 設定屬性
    // Catalina.parentClassLoader
    method.invoke(startupInstance, paramValues);

    catalinaDaemon = startupInstance;
}

initClassLoaders

/**
 * 創建了三個自己的類加載器 commonLoader catalinaLoader sharedLoader
 */
private void initClassLoaders() {
    try {
        commonLoader = createClassLoader("common", null);
        if (commonLoader == null) {
            // no config file, default to this loader - we might be in a 'single' env.
            commonLoader = this.getClass().getClassLoader();
        }
        catalinaLoader = createClassLoader("server", commonLoader);
        // 給 webapp 用
        sharedLoader = createClassLoader("shared", commonLoader);
    } catch (Throwable t) {
        handleThrowable(t);
        log.error("Class loader creation threw exception", t);
        System.exit(1);
    }
}

創建的三個類加載器并不是三個獨立的類加載器, 其結構關系為:

setParentClassLoader

//org.apache.catalina.startup.Catalina#setParentClassLoader
public void setParentClassLoader(ClassLoader parentClassLoader) {
    this.parentClassLoader = parentClassLoader;
}

tomcat 初始化時, 代碼邏輯還是比較簡單的.

主要干了兩件事:

1. 呼叫 initClassLoaders() , 創建了三個自己的類加載器

2. 反射創建了 Catalina 類, 并呼叫了其 setParentClassLoader() 方法, 將 sharedLoader 類加載器設定進去

標籤：Java

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