tomcat源码阅读二--------隐藏的ClassLoader

在看tomcat源码是发现了一个比较有趣的配置文件-------catalina.properties

这个配置文件分为四部分

第一部分：安全设置

第二部分：类加载设置

common.loader

通常情况下，common.loader是已经设置好的，不需要修改。

common.loader包括以下路径：

unpacked classes and resources in $CATALINA_BASE/lib
JAR files in $CATALINA_BASE/lib
unpacked classes and resources in $CATALINA_HOME/lib
JAR files in $CATALINA_HOME/lib

和默认的一些jar包：

annotations-api.jar — JavaEE annotations classes.
catalina.jar — Implementation of the Catalina servlet container portion of Tomcat.
catalina-ant.jar — Tomcat Catalina Ant tasks.
catalina-ha.jar — High availability package.
catalina-tribes.jar — Group communication package.
ecj-*.jar — Eclipse JDT Java compiler.
el-api.jar — EL 2.2 API.
jasper.jar — Tomcat Jasper JSP Compiler and Runtime.
jasper-el.jar — Tomcat Jasper EL implementation.
jsp-api.jar — JSP 2.2 API.
servlet-api.jar — Servlet 3.0 API.
tomcat-api.jar — Several interfaces defined by Tomcat.
tomcat-coyote.jar — Tomcat connectors and utility classes.
tomcat-dbcp.jar — Database connection pool implementation based on package-renamed copy of Apache Commons Pool and Apache Commons DBCP.
tomcat-i18n-**.jar — Optional JARs containing resource bundles for other languages. As default bundles are also included in each individual JAR, they can be safely removed if no internationalization of messages is needed.
tomcat-jdbc.jar — An alternative database connection pool implementation, known as Tomcat JDBC pool. See documentation for more details.
tomcat-util.jar — Common classes used by various components of Apache Tomcat.

这些都是系统和工具类，比如数据库的驱动类库、log 类库可以放到此处，web应用的jar 不要放到common.loader 中。

server.loader 和 shared.loader

在common.loader 加载完后，tomcat启动程序会检查 catalina.properties文件中配置的server.loader和shared.loader是否设置

如果设置，读取 tomcat下对应的server和shared这两个目录的类库。

server和shared是对应tomcat目录下的两个目录,默认的Tomcat7 下这两个目录是没有的。

设置方法：

server.loader=${catalina.base}/server/classes,${catalina.base}/server/lib/*.jar

shared.loader=${catalina.base}/server/classes,${catalina.base}/server/lib/*.jar

同时需要在tomcat目录下创建 server和shared目录结构并将公用的、应用类放到里面。

Bootstrap--->System--->/WEB-INF/classes---> /WEB-INF/lib/*.jar---> Common --->Server --->Shared

  catalinaLoader = createClassLoader("server", commonLoader);
  sharedLoader = createClassLoader("shared", commonLoader);

------------------------------------------------------------------------------------
public void init() throws Exception {

        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);
        //初始化tomcat的守护进程
        catalinaDaemon = startupInstance;

    }

源码在tomcat启动时基本是采用catalinaLoader来加载tomcat自身相关的jar，但catalinaLoader的父Loader就是commonLoader，而且org.apache.catalina.startup.Catalina这个类其实就在common文件夹下面，而在catalina.properties文件中serverLoader配置默认为空，所以我基本任务这里的catalinaLoader就是commonLoader

第三部分：不需要扫描的类设置

第四部分：字符缓存设置

tomcat源码阅读 二--------隐藏的ClassLoader

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