Servlet 在 spring 中的应用

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public interface ServletContextListener extends EventListener {
    // 上下文初始化
    void contextInitialized(ServletContextEvent var1);
	// 销毁
    void contextDestroyed(ServletContextEvent var1);
}

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public void contextInitialized(ServletContextEvent event) {
    this.initWebApplicationContext(event.getServletContext());
}

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public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
    if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {
        throw new IllegalStateException("Cannot initialize context because there is already a root application context present - check whether you have multiple ContextLoader* definitions in your web.xml!");
    } else {
        Log logger = LogFactory.getLog(ContextLoader.class);
        servletContext.log("Initializing Spring root WebApplicationContext");
        if (logger.isInfoEnabled()) {
            logger.info("Root WebApplicationContext: initialization started");
        }

        long startTime = System.currentTimeMillis();

        try {
            if (this.context == null) {
                this.context = this.createWebApplicationContext(servletContext);
            }

            if (this.context instanceof ConfigurableWebApplicationContext) {
                ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext)this.context;
                if (!cwac.isActive()) {
                    if (cwac.getParent() == null) {
                        ApplicationContext parent = this.loadParentContext(servletContext);
                        cwac.setParent(parent);
                    }

                    this.configureAndRefreshWebApplicationContext(cwac, servletContext);
                }
            }

            servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);
            ClassLoader ccl = Thread.currentThread().getContextClassLoader();
            if (ccl == ContextLoader.class.getClassLoader()) {
                currentContext = this.context;
            } else if (ccl != null) {
                currentContextPerThread.put(ccl, this.context);
            }

            if (logger.isDebugEnabled()) {
                logger.debug("Published root WebApplicationContext as ServletContext attribute with name [" + WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + "]");
            }

            if (logger.isInfoEnabled()) {
                long elapsedTime = System.currentTimeMillis() - startTime;
                logger.info("Root WebApplicationContext: initialization completed in " + elapsedTime + " ms");
            }

            return this.context;
        } catch (RuntimeException var8) {
            logger.error("Context initialization failed", var8);
            servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, var8);
            throw var8;
        } catch (Error var9) {
            logger.error("Context initialization failed", var9);
            servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, var9);
            throw var9;
        }
    }
}

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if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {
    throw new IllegalStateException("Cannot initialize context because there is already a root application context present - check whether you have multiple ContextLoader* definitions in your web.xml!");
}

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if (this.context == null) {
    this.context = this.createWebApplicationContext(servletContext);
}

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servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);

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protected ClassLoader(ClassLoader parent) {
    this(checkCreateClassLoader(), null, parent);
}

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public AbstractApplicationContext(@Nullable ApplicationContext parent) {
    this();
    this.setParent(parent);
}

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protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {
//。。。
    configLocationParam = sc.getInitParameter("contextConfigLocation");
  //。。。
}

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public class DispatcherServlet extends FrameworkServlet {

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public interface Servlet {
	// 初始化，配置 contextConfigLoacation
    void init(ServletConfig var1) throws ServletException;

    ServletConfig getServletConfig();

    void service(ServletRequest var1, ServletResponse var2) throws ServletException, IOException;

    String getServletInfo();

    void destroy();
}

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public interface ServletConfig {
    String getServletName();

    ServletContext getServletContext();

    String getInitParameter(String var1);

    Enumeration getInitParameterNames();
}

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public void init(ServletConfig config) throws ServletException {
    this.config = config;
    this.init();
}

public void init() throws ServletException {
}

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public final void init() throws ServletException {
    if (this.logger.isDebugEnabled()) {
        this.logger.debug("Initializing servlet '" + this.getServletName() + "'");
    }

    PropertyValues pvs = new HttpServletBean.ServletConfigPropertyValues(this.getServletConfig(), this.requiredProperties);
    if (!pvs.isEmpty()) {
        try {
            // webxml 配置项和字段进行了一个绑定
            BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
            ResourceLoader resourceLoader = new ServletContextResourceLoader(this.getServletContext());
            bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, this.getEnvironment()));
            this.initBeanWrapper(bw);
            bw.setPropertyValues(pvs, true);
        } catch (BeansException var4) {
            if (this.logger.isErrorEnabled()) {
                this.logger.error("Failed to set bean properties on servlet '" + this.getServletName() + "'", var4);
            }

            throw var4;
        }
    }

    this.initServletBean();
    if (this.logger.isDebugEnabled()) {
        this.logger.debug("Servlet '" + this.getServletName() + "' configured successfully");
    }

}

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protected final void initServletBean() throws ServletException {
    this.getServletContext().log("Initializing Spring FrameworkServlet '" + this.getServletName() + "'");
    if (this.logger.isInfoEnabled()) {
        this.logger.info("FrameworkServlet '" + this.getServletName() + "': initialization started");
    }

    long startTime = System.currentTimeMillis();

    try {
        this.webApplicationContext = this.initWebApplicationContext();
        this.initFrameworkServlet();
    } catch (ServletException var5) {
        this.logger.error("Context initialization failed", var5);
        throw var5;
    } catch (RuntimeException var6) {
        this.logger.error("Context initialization failed", var6);
        throw var6;
    }

    if (this.logger.isInfoEnabled()) {
        long elapsedTime = System.currentTimeMillis() - startTime;
        this.logger.info("FrameworkServlet '" + this.getServletName() + "': initialization completed in " + elapsedTime + " ms");
    }

}

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protected WebApplicationContext initWebApplicationContext() {
    WebApplicationContext rootContext = WebApplicationContextUtils.getWebApplicationContext(this.getServletContext());
    WebApplicationContext wac = null;
    if (this.webApplicationContext != null) {
        wac = this.webApplicationContext;
        if (wac instanceof ConfigurableWebApplicationContext) {
            ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext)wac;
            if (!cwac.isActive()) {
                if (cwac.getParent() == null) {
                    cwac.setParent(rootContext);
                }

                this.configureAndRefreshWebApplicationContext(cwac);
            }
        }
    }

    if (wac == null) {
        wac = this.findWebApplicationContext();
    }

    if (wac == null) {
        wac = this.createWebApplicationContext(rootContext);
    }

    if (!this.refreshEventReceived) {
        this.onRefresh(wac);
    }

    if (this.publishContext) {
        String attrName = this.getServletContextAttributeName();
        this.getServletContext().setAttribute(attrName, wac);
        if (this.logger.isDebugEnabled()) {
            this.logger.debug("Published WebApplicationContext of servlet '" + this.getServletName() + "' as ServletContext attribute with name [" + attrName + "]");
        }
    }

    return wac;
}

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WebApplicationContext wac = null;

// 等于空，我去find，不一定要自己去创建。
// 创建的时候，把 Servlet上下文 的 parent 提交给了 ROOT

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public interface Filter {
    void init(FilterConfig var1) throws ServletException;

    void doFilter(ServletRequest var1, ServletResponse var2, FilterChain var3) throws IOException, ServletException;

    void destroy();
}