在几乎所有的web应用中都需要对访问者(用户)进行权限管理, 因为我们希望某些页面只对特定的用户开放, 以及某些操作只有符合身份的用户才能进行. 这之中涉及到了身份验证和权限管理. 只有单用户系统和多用户单权限系统才不需要权限管理.

在本文中, 使用了基于组的权限管理, 并在Spring框架下利用HandlerInterceptorAdapter和Hibernate进行实现.

User的结构是:
public class User {

private int id;

private String name;

private String password;

private Set<String> groups = new HashSet<String>();
}

UserGroup表:

user:int
group:String

使用联合主键, 在Java中没有对应的类.

Hibernate映射文件是:
<hibernate-mapping auto-import="true" default-lazy="false">
<class name="net.ideawu.User" table="User">
<cache usage="read-write" />
<id name="id" column="id">
<generator class="native"/>
</id>
<property name="name" column="name"/>
<property name="password" column="password"/>
<set name="groups" table="UserGroup" cascade="save-update" lazy="false">
<key column="user" />
<element column="`group`" type="string" />
</set>
</class>
</hibernate-mapping>
一切的身份验证交给一个继承HandlerInterceptorAdapter的类来做:
import org.springframework.web.util.UrlPathHelper;
import org.springframework.util.AntPathMatcher;
import org.springframework.util.PathMatcher;
...

public class AuthorizeInterceptor extends HandlerInterceptorAdapter {

private UrlPathHelper urlPathHelper = new UrlPathHelper();

private PathMatcher pathMatcher = new AntPathMatcher();

private  Properties groupMappings;

/**
* Attach URL paths to group.
*/
public void setGroupMappings(Properties groupMappings) {
this.groupMappings = groupMappings;
}

public boolean preHandle(HttpServletRequest request,
HttpServletResponse response,
Object handler) throws Exception {
String url = urlPathHelper.getLookupPathForRequest(request);
String group = lookupGroup(url); // 找出资源所需要的权限, 即组名
if(group == null){ // 所请求的资源不需要保护.
return true;
}
// 如果已经登录, 一个User实例被保存在session中.
User loginUser = (User)request.getSession().getAttribute("loginUser");
ModelAndView mav = new ModelAndView("system/authorizeError");
if(loginUser == null){
mav.addObject("errorMsg", "你还没有登录!");
throw new ModelAndViewDefiningException(mav);
}else{
if(!loginUser.getGroups().contains(group)){
mav.addObject("errorMsg", "授权失败! 你不在 <b>" + group + "</b> 组!");
throw new ModelAndViewDefiningException(mav);
}
return true;
}
}

/*
* 查看 org.springframework.web.servlet.handler.AbstractUrlHandlerMapping.lookupHandler()
* Ant模式的最长子串匹配法.
*/
private String lookupGroup(String url){
String group =  groupMappings.getProperty(url);
if (group == null) {
String bestPathMatch = null;
for (Iterator it = this.groupMappings.keySet().iterator(); it.hasNext();) {
String registeredPath = (String) it.next();
if (this.pathMatcher.match(registeredPath, url) &&
(bestPathMatch == null || bestPathMatch.length() <= registeredPath.length())) {
group = this.groupMappings.getProperty(registeredPath);
bestPathMatch = registeredPath;
}
}
}
return group;
}
}

下面我们需要在Spring的应用上下文配置文件中设置:

<bean id="authorizeInterceptor" class="net.ideawu.AuthorizeInterceptor">
	<property name="groupMappings">
		<value>
			<!-- Attach URL paths to group -->
			/admin/*=admin
		</value>
	</property>
</bean>

<bean id="simpleUrlHandlerMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
	<property name="interceptors">
		<list>
			<ref bean="authorizeInterceptor" />
		</list>
	</property>
	<property name="mappings">
		<value>
			/index.do=indexController
			/browse.do=browseController
			/admin/removeArticle.do=removeArticleController
		</value>
	</property>
</bean>

注意到"/admin/*=admin", 所以/admin目录下的所有资源只有在admin组的用户才能访问, 这样就不用担心普通访客删除文章了. 使用这种方法, 你不需要在removeArticleController中作身份验证和权限管理, 一切都交给AuthorizeInterceptor.