Apache Shiro學習筆記（七）EnvironmentLoaderListener

魯春利的工作筆記，好記性不如爛筆頭

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web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xmlns="http://java.sun.com/xml/ns/javaee" 
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
        http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" 
    id="WebApp_ID" version="3.0">
  <display-name>Invicme</display-name>
  <listener>
    <listener-class>org.apache.shiro.web.env.EnvironmentLoaderListener</listener-class>
  </listener>
  
  <context-param>
    <param-name>shiroEnvironmentClass</param-name>
    <param-value>org.apache.shiro.web.env.IniWebEnvironment</param-value>
  </context-param>
  <context-param>
    <param-name>shiroConfigLocations</param-name>
    <param-value>classpath:shiro/shiro-form-filter.ini</param-value>
  </context-param>
  
  <filter>
    <filter-name>ShiroFilter</filter-name>
    <filter-class>org.apache.shiro.web.servlet.ShiroFilter</filter-class>
  </filter>
  
  <filter-mapping>
    <filter-name>ShiroFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  <session-config>
    <session-timeout>30</session-timeout>
  </session-config>
  
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>

web.xml的配置中<context-param>的作用
1. 啓動一個WEB項目的時候,容器(如:Tomcat)會去讀它的配置文件web.xml
    讀兩個節點: <listener></listener> 和 <context-param></context-param>
2. 緊接着,容器創建一個ServletContext(上下文),這個WEB項目所有部分都將共享這個上下文
3. 容器將<context-param></context-param>轉化爲鍵值對,並交給ServletContext
4. 容器創建<listener></listener>中的類實例,即創建監聽
5. 在監聽中會有contextInitialized(ServletContextEvent args)初始化方法
    在這個方法中獲得ServletContext = ServletContextEvent.getServletContext();
    context-param的值 = ServletContext.getInitParameter("context-param的鍵");
6. 得到這個context-param的值之後,可以做一些其他操作了

ShiroFilter

package org.apache.shiro.web.servlet;

import org.apache.shiro.web.env.WebEnvironment;
import org.apache.shiro.web.filter.mgt.FilterChainResolver;
import org.apache.shiro.web.util.WebUtils;

/**
 * @see org.apache.shiro.web.env.EnvironmentLoader EnvironmentLoader
 * @see org.apache.shiro.web.env.EnvironmentLoaderListener EnvironmentLoaderListener
 * @see <a href="http://shiro.apache.org/web.html">Apache Shiro Web Documentation</a>
 * @since 1.2
 */
public class ShiroFilter extends AbstractShiroFilter {

    /**
     * @see org.apache.shiro.web.env.EnvironmentLoaderListener
     * @since 1.2
     */
    @Override
    public void init() throws Exception {
        // 
        WebEnvironment env = WebUtils.getRequiredWebEnvironment(getServletContext());

        setSecurityManager(env.getWebSecurityManager());

        FilterChainResolver resolver = env.getFilterChainResolver();
        if (resolver != null) {
            setFilterChainResolver(resolver);
        }
    }
}

輔助工具類WebUtils

package org.apache.shiro.web.util;

public class WebUtils {
    
    public static WebEnvironment getRequiredWebEnvironment(ServletContext sc)
            throws IllegalStateException {

        WebEnvironment we = getWebEnvironment(sc);
        if (we == null) {
            throw new IllegalStateException("No WebEnvironment found: no EnvironmentLoaderListener registered?");
        }
        return we;
    }
    
    public static WebEnvironment getWebEnvironment(ServletContext sc) {
        return getWebEnvironment(sc, EnvironmentLoader.ENVIRONMENT_ATTRIBUTE_KEY);
    }
    
    public static WebEnvironment getWebEnvironment(ServletContext sc, String attrName) {
        if (sc == null) {
            // 異常
        }
        Object attr = sc.getAttribute(attrName);
        if (attr == null) {    // 返回null（ServletContext中無該屬性）
            return null;
        }
        if (attr instanceof RuntimeException) {
            // 異常
        }
        if (attr instanceof Error) {
            // 異常
        }
        if (attr instanceof Exception) {
            // 異常
        }
        if (!(attr instanceof WebEnvironment)) {
            // 異常
        }
        // 獲取到實際的值
        return (WebEnvironment) attr;
    }
}

ServletContext中的EnvironmentLoader.ENVIRONMENT_ATTRIBUTE_KEY屬性是在什麼時候設置的呢？

WebEnvironment的類圖結構

EnvironmentLoaderListener

package org.apache.shiro.web.env;

public class EnvironmentLoaderListener extends EnvironmentLoader implements ServletContextListener {
    // Web應用被初始化時默認調用的方法
    public void contextInitialized(ServletContextEvent sce) {
        // 調用父類EnvironmentLoader的initEnvironment方法
        initEnvironment(sce.getServletContext());
    }
    
    // Web應用被銷燬時默認調用的方法（reload時是會調用該方法）
    public void contextDestroyed(ServletContextEvent sce) {
        destroyEnvironment(sce.getServletContext());
    }
}

EnvironmentLoader

package org.apache.shiro.web.env;

public class EnvironmentLoader {
    // 在web.xml文件中指定WebEnvironment的實現類
    public static final String ENVIRONMENT_CLASS_PARAM = "shiroEnvironmentClass";
    // 在web.xml文件中指定ini文件路徑（不指定則默認加載/WEB-INF/shiro.ini）
    public static final String CONFIG_LOCATIONS_PARAM = "shiroConfigLocations";
    
    // 初始化Environment實例
    public WebEnvironment initEnvironment(ServletContext servletContext) throws IllegalStateException {

        if (servletContext.getAttribute(ENVIRONMENT_ATTRIBUTE_KEY) != null) {
            // 第一次Web應用啓動時上下文中已經存在該KEY的屬性，說明web.xml文件配置有問題，可能有多個EnvironmentLoader*的定義
            // 異常
        }

        // 記錄日誌
        servletContext.log("Initializing Shiro environment");
        log.info("Starting Shiro environment initialization.");

        // 記錄當前時間
        long startTime = System.currentTimeMillis();

        try {
            // 獲取WebEnvironment類的實例
            WebEnvironment environment = createEnvironment(servletContext);
            // 在ServletContext中設置KEY，設置完成後在WebUtils中就可以獲取到了
            servletContext.setAttribute(ENVIRONMENT_ATTRIBUTE_KEY, environment);

            // 在日誌中輸出ServletContext中設置WebEnvironment耗費的時間（毫秒）
            if (log.isInfoEnabled()) {
                long elapsed = System.currentTimeMillis() - startTime;
                log.info("Shiro environment initialized in {} ms.", elapsed);
            }

            return environment;
        } catch (RuntimeException ex) {
            // 異常
        } catch (Error err) {
            // 異常
        }
    }
    
    // 在給定的ServletContext中設置WebEnvironment
    protected WebEnvironment createEnvironment(ServletContext sc) {

        Class<?> clazz = determineWebEnvironmentClass(sc);
        if (!MutableWebEnvironment.class.isAssignableFrom(clazz)) {    // native方法，底層JVM實現
           // 異常
        }

        // 從ServletContext中獲取shiroConfigLocations屬性的值（classpath:shiro/shiro-form-filter.ini）
        String configLocations = sc.getInitParameter(CONFIG_LOCATIONS_PARAM);
        boolean configSpecified = StringUtils.hasText(configLocations);

        if (configSpecified && !(ResourceConfigurable.class.isAssignableFrom(clazz))) {
            // 異常
        }
        // 獲取類的實例（ClassUtils.newInstance(clazz) ==>  return clazz.newInstance();）
        MutableWebEnvironment environment = (MutableWebEnvironment) ClassUtils.newInstance(clazz);
        // 調用父類DefaultWebEnvironment的setServletContext
        environment.setServletContext(sc);

        if (configSpecified && (environment instanceof ResourceConfigurable)) {
            // 調用父類ResourceBasedWebEnvironment的setConfigLocations
            ((ResourceConfigurable) environment).setConfigLocations(configLocations);
        }

        customizeEnvironment(environment);
        // LifecycleUtils.init中會調用environment.init方法（IniWebEnvironment.init()）
        LifecycleUtils.init(environment);
        
        // 返回得到的WebEnvironment類的實例（IniWebEnvironment的實例）
        return environment;
    }
    
    // 獲取WebEnvironment的Class類對象
    protected Class<?> determineWebEnvironmentClass(ServletContext servletContext) {
        // ENVIRONMENT_CLASS_PARAM = "shiroEnvironmentClass";獲取web.xml文件中聲明的屬性值
        String className = servletContext.getInitParameter(ENVIRONMENT_CLASS_PARAM);
        if (className != null) {
            try {
                // web.xml配置的參數對應className=org.apache.shiro.web.env.IniWebEnvironment
                return ClassUtils.forName(className);    
            } catch (UnknownClassException ex) {
                // 異常
            }
        } else {    // 如果未配置則使用該IniWebEnvironment類
            return IniWebEnvironment.class;
        }
    }
    
    // 空的方法體，可以實現自定義的邏輯
    protected void customizeEnvironment(WebEnvironment environment) {
        // ......
    }
}