Shiro源码分析-初始化-Realm

在上一篇介绍SecurityManager的初始化过程中，也有realm的粗略介绍。 
realm的概念在安全领域随处可见： 
各种中间件的realm、spring security的realm、shiro的realm。。。如下： 
tomcat的realm： http://tomcat.apache.org/tomcat-7.0-doc/realm-howto.html 
weblogic的realm：http://edocs.weblogicfans.net/wls/docs92/secintro/realm_chap.html 
spring security的realm http://www.oschina.net/translate/spring-security-basic-authentication?lang=eng 
tomcat官网对realm的定义是这样的：

A Realm is a "database" of usernames and passwords that identify valid users of a web application (or set of web applications), plus an enumeration of the list of roles associated with each valid user. You can think of roles as similar to groups in Unix-like operating systems, because access to specific web application resources is granted to all users possessing a particular role (rather than enumerating the list of associated usernames). A particular user can have any number of roles associated with their username.

我个人理解realm相当于管理账号密码、角色、权限的仓库。有异议的，欢迎一起讨论。 
原谅我的啰嗦，先进入正题。 
Shiro的realm类图如下：

由图可见，Realm主要还是认证、授权服务，并提供cache支持。 
shiro提供了几种realm可供项目选择，一般项目中比较常用的应该是JdbcRealm，运行测试用例一般使用IniRealm。 
开涛在讲解身份验证的章节中演示了两种realm的方式（ini、jdbc） 
http://jinnianshilongnian.iteye.com/blog/2019547 
一、Ini方式的realm：

、

从图中可看出，shiro对于通过文本方式定义账号、权限提供了Ini、Properties两种方式。SimpleAccountRealm类的users、roles集合分别用来保存账号、权限信息。 
还记得在前一篇介绍SecurityManager初始化中，关于realm的创建了么？

没错，就是这里。根据ini配置中的users、roles段落来解析成IniRealm的对象实例。 
下面，简单跟踪一下代码吧：

//IniRealm构造函数会调用此方法完成解析操作
  private void processDefinitions(Ini ini) {
    if (CollectionUtils.isEmpty(ini)) {
      log.warn("{} defined, but the ini instance is null or empty.", getClass().getSimpleName());
      return;
    }

    Ini.Section rolesSection = ini.getSection(ROLES_SECTION_NAME);
    if (!CollectionUtils.isEmpty(rolesSection)) {
      log.debug("Discovered the [{}] section.  Processing...", ROLES_SECTION_NAME);
      //解析roles段落交给父类完成
      processRoleDefinitions(rolesSection);
    }

    Ini.Section usersSection = ini.getSection(USERS_SECTION_NAME);
    if (!CollectionUtils.isEmpty(usersSection)) {
      log.debug("Discovered the [{}] section.  Processing...", USERS_SECTION_NAME);
      //解析users段落交给父类完成
      processUserDefinitions(usersSection);
    } else {
      ......
    }
  }

niRealm的父类TextConfigurationRealm根据子类的users、roles配置完成解析操作

//解析roles，并构造SimpleRole对象
  protected void processRoleDefinitions(Map<String, String> roleDefs) {
    if (roleDefs == null || roleDefs.isEmpty()) {
      return;
    }
    for (String rolename : roleDefs.keySet()) {
      String value = roleDefs.get(rolename);

      SimpleRole role = getRole(rolename);
      if (role == null) {
        role = new SimpleRole(rolename);
        add(role);
      }

      Set<Permission> permissions = PermissionUtils.resolveDelimitedPermissions(value, getPermissionResolver());
      role.setPermissions(permissions);
    }
  }

//解析roles，并构造SimpleRole对象
  protected void processRoleDefinitions(Map<String, String> roleDefs) {
    if (roleDefs == null || roleDefs.isEmpty()) {
      return;
    }
    for (String rolename : roleDefs.keySet()) {
      String value = roleDefs.get(rolename);

      SimpleRole role = getRole(rolename);
      if (role == null) {
        role = new SimpleRole(rolename);
        add(role);
      }

      Set<Permission> permissions = PermissionUtils.resolveDelimitedPermissions(value, getPermissionResolver());
      role.setPermissions(permissions);
    }
  }

//解析users，并构造SimpleAccount对象
  protected void processUserDefinitions(Map<String, String> userDefs) {
    if (userDefs == null || userDefs.isEmpty()) {
      return;
    }
    for (String username : userDefs.keySet()) {

      String value = userDefs.get(username);

      String[] passwordAndRolesArray = StringUtils.split(value);

      String password = passwordAndRolesArray[];

      SimpleAccount account = getUser(username);
      if (account == null) {
        account = new SimpleAccount(username, password, getName());
        add(account);
      }
      account.setCredentials(password);

      if (passwordAndRolesArray.length > ) {
        for (int i = ; i < passwordAndRolesArray.length; i++) {
          String rolename = passwordAndRolesArray[i];
          account.addRole(rolename);

          SimpleRole role = getRole(rolename);
          if (role != null) {
            account.addObjectPermissions(role.getPermissions());
          }
        }
      } else {
        account.setRoles(null);
      }
    }
  }

二、Jdbc方式的realm：

jdbcRealm=org.apache.shiro.realm.jdbc.JdbcRealm
dataSource=com.alibaba.druid.pool.DruidDataSource
dataSource.driverClassName=com.mysql.jdbc.Driver
dataSource.url=jdbc:mysql://localhost:3306/shiro
dataSource.username=root
dataSource.password=root
jdbcRealm.dataSource=$dataSource
securityManager.realms=$jdbcRealm

由于shiro支持在ini中配置依赖注入，那么JdbcRealm中的sql信息也是可配置的。

jdbcRealm.authenticationQuery=用户查询
jdbcRealm.userRolesQuery=角色查询
jdbcRealm.permissionsQuery=权限查询

当然，如果不习惯这种方式，可以直接自定义Realm，并继承自AuthorizingRealm或者JdbcRealm都可以。 
JdbcRealm通过查询数据库的认证实体、角色、权限，构造的对象分别是：SimpleAuthenticationInfo、SimpleAuthorizationInfo。 
实际上，IniRealm方式构造的SimpleAccount、SimpleRole与JdbcRealm方式构造的SimpleAuthenticationInfo、SimpleAuthorizationInfo一一对应，且都实现认证接口AuthenticationInfo、授权接口AuthorizationInfo。关于更详细的讲解放在后面的认证、授权部分。 
三、RealmFactory： 
Shiro不仅支持Realm类型，还支持RealmFactory类型，在初始化的时候，如果配置中存在RealmFactory实现类，则直接调用其Collection<Realm> getRealms()方法。 
该方式在多个realm的情况下很实用。 
四、与Spring Security的比较： 
Spring Security的Realm仅仅是用在basic认证方式。 
Shiro的realm与Spring Security的UserDetailsService非常相似。但是命名确非常迷糊，下面进一步分析： 
先看UserDetailsService接口定义：

//根据用户名称获取UserDetails
public interface UserDetailsService {
    UserDetails loadUserByUsername(String username)
        throws UsernameNotFoundException, DataAccessException;
}

UserDetails接口定义：

public interface UserDetails extends Serializable {
  //获取授权的集合
  Collection<GrantedAuthority> getAuthorities();
  String getPassword();
  String getUsername();
  boolean isAccountNonExpired();
  boolean isAccountNonLocked();
  boolean isCredentialsNonExpired();
  boolean isEnabled();
}

由此可看出，Spring Security的UserDetailsService获取的UserDetails已经拥有了授权信息。只是从接口命名中无法得知。 
而Shiro的realm是把职责分解了，层次更清晰些。 
后续在分析shiro的过程中，会增加与SpringSecurity的比较。