[簡介]
對于一個典型的Web應用，完善的認證和授權機制是必不可少的，在SpringFramework中，Juergen Hoeller提供的范例JPetStore給了一些這方面的介紹，但還遠遠不夠，Acegi是一個專門為SpringFramework提供安全機制的 項目，全稱為Acegi Security System for Spring，當前版本為0.5.1，就其目前提供的功能，應該可以滿足絕大多數應用的需求。
本文的主要目的是希望能夠說明如何在基于Spring構架的Web應用中使用Acegi，而不是詳細介紹其中的每個接口、每個類。注意，即使對已經存在的Spring應用，通過下面介紹的步驟，也可以馬上享受到Acegi提供的認證和授權。
[基礎工作]在你的Web應用的lib中添加Acegi下載包中的acegi-security.jar[web.xml]實現認證和授權的最常用的方法是通過filter，Acegi亦是如此，通常Acegi需要在web.xml添加以下5個filter:
<filter>
<filter-name>Acegi Channel Processing Filter</filter-name>
<filter-class>net.sf.acegisecurity.util.FilterToBeanProxy</filter-class>
<init-param>
<param-name>targetClass</param-name>
<param-value>net.sf.acegisecurity.securechannel.ChannelProcessingFilter</param-value>
</init-param>
</filter>
<filter>
<filter-name>Acegi Authentication Processing Filter</filter-name>
<filter-class>net.sf.acegisecurity.util.FilterToBeanProxy</filter-class>
<init-param>
<param-name>targetClass</param-name>
<param-value>net.sf.acegisecurity.ui.webapp.AuthenticationProcessingFilter</param-value>
</init-param>
</filter>
<filter>
<filter-name>Acegi HTTP BASIC Authorization Filter</filter-name>
<filter-class>net.sf.acegisecurity.util.FilterToBeanProxy</filter-class>
<init-param>
<param-name>targetClass</param-name>
<param-value>net.sf.acegisecurity.ui.basicauth.BasicProcessingFilter</param-value>
</init-param>
</filter>
<filter>
<filter-name>Acegi Security System for Spring Auto Integration Filter</filter-name>
<filter-class>net.sf.acegisecurity.ui.AutoIntegrationFilter</filter-class>
</filter>
<filter>
<filter-name>Acegi HTTP Request Security Filter</filter-name>
<filter-class>net.sf.acegisecurity.util.FilterToBeanProxy</filter-class>
<init-param>
<param-name>targetClass</param-name>
<param-value>net.sf.acegisecurity.intercept.web.SecurityEnforcementFilter</param-value>
</init-param>
</filter>
最先引起迷惑的是net.sf.acegisecurity.util.FilterToBeanProxy，Acegi自己的文檔上解釋是： “What FilterToBeanProxy does is delegate the Filter's methods through to a bean which is obtained from the
Spring application context. This enables the bean to benefit from the Spring application context lifecycle support and configuration flexibility.”，如希望深究的話，去看看源代碼應該不難理解。
再下來就是添加filter-mapping了：
<filter-mapping>
<filter-name>Acegi Channel Processing Filter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<filter-mapping>
<filter-name>Acegi Authentication Processing Filter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<filter-mapping>
<filter-name>Acegi HTTP BASIC Authorization Filter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<filter-mapping>
<filter-name>Acegi Security System for Spring Auto Integration Filter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<filter-mapping>
<filter-name>Acegi HTTP Request Security Filter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
這里，需要注意以下兩點：
1) 這幾個filter的順序是不能更改的，順序不對將無法正常工作；
2) 如果你的應用不需要安全傳輸，如https，則將"Acegi Channel Processing Filter"相關內容注釋掉即可；
3) 如果你的應用不需要Spring提供的遠程訪問機制，如Hessian and Burlap，將"Acegi HTTP BASIC Authorization
Filter"相關內容注釋掉即可。
[applicationContext.xml]
接下來就是要添加applicationContext.xml中的內容了，從剛才FilterToBeanFactory的解釋可以看出，真正的filter都
在Spring的applicationContext中管理：
1) 首先，你的數據庫中必須具有保存用戶名和密碼的table，Acegi要求table的schema必須如下：
CREATE TABLE users (
username VARCHAR(50) NOT NULL PRIMARY KEY,
password VARCHAR(50) NOT NULL,
enabled BIT NOT NULL
);
CREATE TABLE authorities (
username VARCHAR(50) NOT NULL,
authority VARCHAR(50) NOT NULL
);
CREATE UNIQUE INDEX ix_auth_username ON authorities ( username, authority );
ALTER TABLE authorities ADD CONSTRAINT fk_authorities_users foreign key (username) REFERENCES users
(username);
2) 添加訪問你的數據庫的datasource和Acegi的jdbcDao，如下：
<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
<property name="driverClassName"><value>${jdbc.driverClassName}</value></property>
<property name="url"><value>${jdbc.url}</value></property>
<property name="username"><value>${jdbc.username}</value></property>
<property name="password"><value>${jdbc.password}</value></property>
</bean>
<bean id="jdbcDaoImpl" class="net.sf.acegisecurity.providers.dao.jdbc.JdbcDaoImpl">
<property name="dataSource"><ref bean="dataSource"/></property>
</bean>
3) 添加DaoAuthenticationProvider:
<bean id="daoAuthenticationProvider" class="net.sf.acegisecurity.providers.dao.DaoAuthenticationProvider">
<property name="authenticationDao"><ref bean="authenticationDao"/></property>
<property name="userCache"><ref bean="userCache"/></property>
</bean>
<bean id="userCache" class="net.sf.acegisecurity.providers.dao.cache.EhCacheBasedUserCache">
<property name="minutesToIdle"><value>5</value></property>
</bean>
如果你需要對密碼加密，則在daoAuthenticationProvider中加入：<property name="passwordEncoder"><ref
bean="passwordEncoder"/></property>，Acegi提供了幾種加密方法，詳細情況可看包
net.sf.acegisecurity.providers.encoding
4) 添加authenticationManager:
<bean id="authenticationManager" class="net.sf.acegisecurity.providers.ProviderManager">
<property name="providers">
<list>
<ref bean="daoAuthenticationProvider"/>
</list>
</property>
</bean>
5) 添加accessDecisionManager:
<bean id="accessDecisionManager" class="net.sf.acegisecurity.vote.AffirmativeBased">
<property name="allowIfAllAbstainDecisions">
<value>false</value>
</property>
<property name="decisionVoters">
<list><ref bean="roleVoter"/></list>
</property>
</bean>
<bean id="roleVoter" class="net.sf.acegisecurity.vote.RoleVoter"/>
6) 添加authenticationProcessingFilterEntryPoint:
<bean id="authenticationProcessingFilterEntryPoint"
class="net.sf.acegisecurity.ui.webapp.AuthenticationProcessingFilterEntryPoint">
<property name="loginFormUrl"><value>/acegilogin.jsp</value></property>
<property name="forceHttps"><value>false</value></property>
</bean>
其中acegilogin.jsp是登陸頁面，一個最簡單的登錄頁面如下：
<%@ taglib prefix='c' uri='http://java.sun.com/jstl/core' %>
<%@ page import="net.sf.acegisecurity.ui.AbstractProcessingFilter" %>
<%@ page import="net.sf.acegisecurity.AuthenticationException" %>
<html>
<head>
<title>Login</title>
</head>
<body>
<h1>Login</h1>
<form action="<c:url value='j_acegi_security_check'/>" method="POST">
<table>
<tr><td>User:</td><td><input type='text' name='j_username'></td></tr>
<tr><td>Password:</td><td><input type='password' name='j_password'></td></tr>
<tr><td colspan='2'><input name="submit" type="submit"></td></tr>
<tr><td colspan='2'><input name="reset" type="reset"></td></tr>
</table>
</form>
</body>
</html>
7) 添加filterInvocationInterceptor:
<bean id="filterInvocationInterceptor"
class="net.sf.acegisecurity.intercept.web.FilterSecurityInterceptor">
<property name="authenticationManager">
<ref bean="authenticationManager"/>
</property>
<property name="accessDecisionManager">
<ref bean="accessDecisionManager"/>
</property>
<property name="objectDefinitionSource">
<value>
CONVERT_URL_TO_LOWERCASE_BEFORE_COMPARISON
\A/sec/administrator.*\Z=ROLE_SUPERVISOR
\A/sec/user.*\Z=ROLE_TELLER
</value>
</property>
</bean>
這里請注意，要objectDefinitionSource中定義哪些頁面需要權限訪問，需要根據自己的應用需求進行修改，我上面給出
的定義的意思是這樣的：
a. CONVERT_URL_TO_LOWERCASE_BEFORE_COMPARISON意思是在比較請求路徑時全部轉換為小寫
b. \A/sec/administrator.*\Z=ROLE_SUPERVISOR意思是只有權限為ROLE_SUPERVISOR才能訪問/sec/administrator*的頁面
c. \A/sec/user.*\Z=ROLE_TELLER意思是只有權限為ROLE_TELLER的用戶才能訪問/sec/user*的頁面
8) 添加securityEnforcementFilter:
<bean id="securityEnforcementFilter" class="net.sf.acegisecurity.intercept.web.SecurityEnforcementFilter">
<property name="filterSecurityInterceptor">
<ref bean="filterInvocationInterceptor"/>
</property>
<property name="authenticationEntryPoint">
<ref bean="authenticationProcessingFilterEntryPoint"/>
</property>
</bean>
9) 添加authenticationProcessingFilter:
<bean id="authenticationProcessingFilter"
class="net.sf.acegisecurity.ui.webapp.AuthenticationProcessingFilter">
<property name="authenticationManager">
<ref bean="authenticationManager"/>
</property>
<property name="authenticationFailureUrl">
<value>/loginerror.jsp</value>
</property>
<property name="defaultTargetUrl">
<value>/</value>
</property>
<property name="filterProcessesUrl">
<value>/j_acegi_security_check</value>
</property>
</bean>
其中authenticationFailureUrl是認證失敗的頁面。
10) 如果需要一些頁面通過安全通道的話，添加下面的配置:
<bean id="channelProcessingFilter" class="net.sf.acegisecurity.securechannel.ChannelProcessingFilter">
<property name="channelDecisionManager">
<ref bean="channelDecisionManager"/>
</property>
<property name="filterInvocationDefinitionSource">
<value>
CONVERT_URL_TO_LOWERCASE_BEFORE_COMPARISON
\A/sec/administrator.*\Z=REQUIRES_SECURE_CHANNEL
\A/acegilogin.jsp.*\Z=REQUIRES_SECURE_CHANNEL
\A/j_acegi_security_check.*\Z=REQUIRES_SECURE_CHANNEL
\A.*\Z=REQUIRES_INSECURE_CHANNEL
</value>
</property>
</bean>
<bean id="channelDecisionManager" class="net.sf.acegisecurity.securechannel.ChannelDecisionManagerImpl">
<property name="channelProcessors">
<list>
<ref bean="secureChannelProcessor"/>
<ref bean="insecureChannelProcessor"/>
</list>
</property>
</bean>
<bean id="secureChannelProcessor" class="net.sf.acegisecurity.securechannel.SecureChannelProcessor"/>
<bean id="insecureChannelProcessor" class="net.sf.acegisecurity.securechannel.InsecureChannelProcessor"/>
[缺少了什么？]
Acegi目前提供了兩種"secure object"，分別對頁面和方法進行安全認證管理，我這里介紹的只是利用
FilterSecurityInterceptor對訪問頁面的權限控制，除此之外，Acegi還提供了另外一個Interceptor——
MethodSecurityInterceptor，它結合runAsManager可實現對對象中的方法的權限控制，使用方法可參看Acegi自帶的文檔
和contact范例。
[最后要說的]
本來以為只是說明如何使用Acegi而已，應該非常簡單，但真正寫起來才發現想要條理清楚的理順所有需要的bean還是很
困難的，但愿我沒有遺漏太多東西，如果我的文章有什么遺漏或錯誤的話，還請參看Acegi自帶的quick-start范例，但請
注意，這個范例是不能直接拿來用的。
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