1. shiro介绍
Apache Shiro是一个强大易用的Java安全框架，提供了认证、授权、加密和会话管理等功能：
对于任何一个应用程序，Shiro都可以提供全面的安全管理服务。并且相对于其他安全框架，Shiro要简单的多。
2. shiro源码概况
先要了解shiro的基本框架(见http://www.cnblogs.com/davidwang456/p/4425145.html)。
然后看一下各个组件之间的关系：
一下内容参考：http://kdboy.iteye.com/blog/1154644
Subject：即“当前操作用户”。但是，在Shiro中，Subject这一概念并不仅仅指人，也可以是第三方进程、后台帐户（Daemon Account）或其他类似事物。它仅仅意味着“当前跟软件交互的东西”。但考虑到大多数目的和用途，你可以把它认为是Shiro的“用户”概念。
Subject代表了当前用户的安全操作，SecurityManager则管理所有用户的安全操作。
SecurityManager：它是Shiro框架的核心，典型的Facade模式，Shiro通过SecurityManager来管理内部组件实例，并通过它来提供安全管理的各种服务。
Realm： Realm充当了Shiro与应用安全数据间的“桥梁”或者“连接器”。也就是说，当对用户执行认证（登录）和授权（访问控制）验证时，Shiro会从应用配置的Realm中查找用户及其权限信息。
从这个意义上讲，Realm实质上是一个安全相关的DAO：它封装了数据源的连接细节，并在需要时将相关数据提供给Shiro。当配置Shiro时，你必须至少指定一个Realm，用于认证和（或）授权。配置多个Realm是可以的，但是至少需要一个。
Shiro内置了可以连接大量安全数据源（又名目录）的Realm，如LDAP、关系数据库（JDBC）、类似INI的文本配置资源以及属性文件等。如果缺省的Realm不能满足需求，你还可以插入代表自定义数据源的自己的Realm实现。
Shiro主要组件还包括：
Authenticator ：认证就是核实用户身份的过程。这个过程的常见例子是大家都熟悉的“用户/密码”组合。多数用户在登录软件系统时，通常提供自己的用户名（当事人）和支持他们的密码（证书）。如果存储在系统中的密码（或密码表示）与用户提供的匹配，他们就被认为通过认证。
Authorizer ：授权实质上就是访问控制 - 控制用户能够访问应用中的哪些内容，比如资源、Web页面等等。
SessionManager ：在安全框架领域，Apache Shiro提供了一些独特的东西：可在任何应用或架构层一致地使用Session API。即，Shiro为任何应用提供了一个会话编程范式 - 从小型后台独立应用到大型集群Web应用。这意味着，那些希望使用会话的应用开发者，不必被迫使用Servlet或EJB容器了。或者，如果正在使用这些容器，开发者现在也可以选择使用在任何层统一一致的会话API，取代Servlet或EJB机制。
CacheManager :对Shiro的其他组件提供缓存支持。
3. 做一个demo，跑shiro的源码，从login开始：
第一步：用户根据表单信息填写用户名和密码，然后调用登陆按钮。内部执行如下：
UsernamePasswordToken token = new UsernamePasswordToken(loginForm.getUsername(), loginForm.getPassphrase());
token.setRememberMe(true);
Subject currentUser = SecurityUtils.getSubject();
currentUser.login(token);
第二步：代理DelegatingSubject继承Subject执行login
public void login(AuthenticationToken token) throws AuthenticationException {
clearRunAsIdentitiesInternal();
Subject subject = securityManager.login(this, token);
PrincipalCollection principals;
String host = null;
if (subject instanceof DelegatingSubject) {
DelegatingSubject delegating = (DelegatingSubject) subject;
//we have to do this in case there are assumed identities - we don't want to lose the 'real' principals:
principals = delegating.principals;
host = delegating.host;
} else {
principals = subject.getPrincipals();
}
if (principals == null || principals.isEmpty()) {
String msg = "Principals returned from securityManager.login( token ) returned a null or " +
"empty value. This value must be non null and populated with one or more elements.";
throw new IllegalStateException(msg);
}
this.principals = principals;
this.authenticated = true;
if (token instanceof HostAuthenticationToken) {
host = ((HostAuthenticationToken) token).getHost();
}
if (host != null) {
this.host = host;
}
Session session = subject.getSession(false);
if (session != null) {
this.session = decorate(session);
} else {
this.session = null;
}
}
第三步：调用DefaultSecurityManager继承SessionsSecurityManager执行login方法
public Subject login(Subject subject, AuthenticationToken token) throws AuthenticationException {
AuthenticationInfo info;
try {
info = authenticate(token);
} catch (AuthenticationException ae) {
try {
onFailedLogin(token, ae, subject);
} catch (Exception e) {
if (log.isInfoEnabled()) {
log.info("onFailedLogin method threw an " +
"exception. Logging and propagating original AuthenticationException.", e);
}
}
throw ae; //propagate
}
Subject loggedIn = createSubject(token, info, subject);
onSuccessfulLogin(token, info, loggedIn);
return loggedIn;
}
第四步：认证管理器AuthenticatingSecurityManager继承RealmSecurityManager执行authenticate方法：
/**
* Delegates to the wrapped {@link org.apache.shiro.authc.Authenticator Authenticator} for authentication.
*/
public AuthenticationInfo authenticate(AuthenticationToken token) throws AuthenticationException {
return this.authenticator.authenticate(token);
}
第五步：抽象认证管理器AbstractAuthenticator继承Authenticator, LogoutAware 执行authenticate方法：
public final AuthenticationInfo authenticate(AuthenticationToken token) throws AuthenticationException {
if (token == null) {
throw new IllegalArgumentException("Method argumet (authentication token) cannot be null.");
}
log.trace("Authentication attempt received for token [{}]", token);
AuthenticationInfo info;
try {
info = doAuthenticate(token);
if (info == null) {
String msg = "No account information found for authentication token [" + token + "] by this " +
"Authenticator instance. Please check that it is configured correctly.";
throw new AuthenticationException(msg);
}
} catch (Throwable t) {
AuthenticationException ae = null;
if (t instanceof AuthenticationException) {
ae = (AuthenticationException) t;
}
if (ae == null) {
//Exception thrown was not an expected AuthenticationException. Therefore it is probably a little more
//severe or unexpected. So, wrap in an AuthenticationException, log to warn, and propagate:
String msg = "Authentication failed for token submission [" + token + "]. Possible unexpected " +
"error? (Typical or expected login exceptions should extend from AuthenticationException).";
ae = new AuthenticationException(msg, t);
}
try {
notifyFailure(token, ae);
} catch (Throwable t2) {
if (log.isWarnEnabled()) {
String msg = "Unable to send notification for failed authentication attempt - listener error?. " +
"Please check your AuthenticationListener implementation(s). Logging sending exception " +
"and propagating original AuthenticationException instead...";
log.warn(msg, t2);
}
}
throw ae;
}
log.debug("Authentication successful for token [{}]. Returned account [{}]", token, info);
notifySuccess(token, info);
return info;
}
第六步：ModularRealmAuthenticator继承AbstractAuthenticator执行doAuthenticate方法
protected AuthenticationInfo doAuthenticate(AuthenticationToken authenticationToken) throws AuthenticationException {
assertRealmsConfigured();
Collection<Realm> realms = getRealms();
if (realms.size() == 1) {
return doSingleRealmAuthentication(realms.iterator().next(), authenticationToken);
} else {
return doMultiRealmAuthentication(realms, authenticationToken);
}
}
接着调用：
/**
* Performs the authentication attempt by interacting with the single configured realm, which is significantly
* simpler than performing multi-realm logic.
*
* @param realm the realm to consult for AuthenticationInfo.
* @param token the submitted AuthenticationToken representing the subject's (user's) log-in principals and credentials.
* @return the AuthenticationInfo associated with the user account corresponding to the specified {@code token}
*/
protected AuthenticationInfo doSingleRealmAuthentication(Realm realm, AuthenticationToken token) {
if (!realm.supports(token)) {
String msg = "Realm [" + realm + "] does not support authentication token [" +
token + "]. Please ensure that the appropriate Realm implementation is " +
"configured correctly or that the realm accepts AuthenticationTokens of this type.";
throw new UnsupportedTokenException(msg);
}
AuthenticationInfo info = realm.getAuthenticationInfo(token);
if (info == null) {
String msg = "Realm [" + realm + "] was unable to find account data for the " +
"submitted AuthenticationToken [" + token + "].";
throw new UnknownAccountException(msg);
}
return info;
}
第七步：AuthenticatingRealm继承CachingRealm执行getAuthenticationInfo方法
public final AuthenticationInfo getAuthenticationInfo(AuthenticationToken token) throws AuthenticationException {
AuthenticationInfo info = getCachedAuthenticationInfo(token); //从缓存中读取
if (info == null) {
//otherwise not cached, perform the lookup:
info = doGetAuthenticationInfo(token); //缓存中读不到，则到数据库或者ldap或者jndi等去读
log.debug("Looked up AuthenticationInfo [{}] from doGetAuthenticationInfo", info);
if (token != null && info != null) {
cacheAuthenticationInfoIfPossible(token, info);
}
} else {
log.debug("Using cached authentication info [{}] to perform credentials matching.", info);
}
if (info != null) {
assertCredentialsMatch(token, info);
} else {
log.debug("No AuthenticationInfo found for submitted AuthenticationToken [{}]. Returning null.", token);
}
return info;
}
1. 从缓存中读取的方法：
/**
* Checks to see if the authenticationCache class attribute is null, and if so, attempts to acquire one from
* any configured {@link #getCacheManager() cacheManager}. If one is acquired, it is set as the class attribute.
* The class attribute is then returned.
*
* @return an available cache instance to be used for authentication caching or {@code null} if one is not available.
* @since 1.2
*/
private Cache<Object, AuthenticationInfo> getAuthenticationCacheLazy() {
if (this.authenticationCache == null) {
log.trace("No authenticationCache instance set. Checking for a cacheManager...");
CacheManager cacheManager = getCacheManager();
if (cacheManager != null) {
String cacheName = getAuthenticationCacheName();
log.debug("CacheManager [{}] configured. Building authentication cache '{}'", cacheManager, cacheName);
this.authenticationCache = cacheManager.getCache(cacheName);
}
}
return this.authenticationCache;
}
2. 从数据库中读取的方法：
JdbcRealm继承 AuthorizingRealm执行doGetAuthenticationInfo方法
protected AuthenticationInfo doGetAuthenticationInfo(AuthenticationToken token) throws AuthenticationException {
UsernamePasswordToken upToken = (UsernamePasswordToken) token;
String username = upToken.getUsername();
// Null username is invalid
if (username == null) {
throw new AccountException("Null usernames are not allowed by this realm.");
}
Connection conn = null;
SimpleAuthenticationInfo info = null;
try {
conn = dataSource.getConnection();
String password = null;
String salt = null;
switch (saltStyle) {
case NO_SALT:
password = getPasswordForUser(conn, username)[0];
break;
case CRYPT:
// TODO: separate password and hash from getPasswordForUser[0]
throw new ConfigurationException("Not implemented yet");
//break;
case COLUMN:
String[] queryResults = getPasswordForUser(conn, username);
password = queryResults[0];
salt = queryResults[1];
break;
case EXTERNAL:
password = getPasswordForUser(conn, username)[0];
salt = getSaltForUser(username);
}
if (password == null) {
throw new UnknownAccountException("No account found for user [" + username + "]");
}
info = new SimpleAuthenticationInfo(username, password.toCharArray(), getName());
if (salt != null) {
info.setCredentialsSalt(ByteSource.Util.bytes(salt));
}
} catch (SQLException e) {
final String message = "There was a SQL error while authenticating user [" + username + "]";
if (log.isErrorEnabled()) {
log.error(message, e);
}
// Rethrow any SQL errors as an authentication exception
throw new AuthenticationException(message, e);
} finally {
JdbcUtils.closeConnection(conn);
}
return info;
}
接着调用sql语句：
private String[] getPasswordForUser(Connection conn, String username) throws SQLException {
String[] result;
boolean returningSeparatedSalt = false;
switch (saltStyle) {
case NO_SALT:
case CRYPT:
case EXTERNAL:
result = new String[1];
break;
default:
result = new String[2];
returningSeparatedSalt = true;
}
PreparedStatement ps = null;
ResultSet rs = null;
try {
ps = conn.prepareStatement(authenticationQuery);
ps.setString(1, username);
// Execute query
rs = ps.executeQuery();
// Loop over results - although we are only expecting one result, since usernames should be unique
boolean foundResult = false;
while (rs.next()) {
// Check to ensure only one row is processed
if (foundResult) {
throw new AuthenticationException("More than one user row found for user [" + username + "]. Usernames must be unique.");
}
result[0] = rs.getString(1);
if (returningSeparatedSalt) {
result[1] = rs.getString(2);
}
foundResult = true;
}
} finally {
JdbcUtils.closeResultSet(rs);
JdbcUtils.closeStatement(ps);
}
return result;
}
其中authenticationQuery定义如下：
protected String authenticationQuery = DEFAULT_AUTHENTICATION_QUERY; protected static final String DEFAULT_AUTHENTICATION_QUERY = "select password from users where username = ?";
4. 小结
Apache Shiro 是功能强大并且容易集成的开源权限框架，它能够完成认证、授权、加密、会话管理等功能。认证和授权为权限控制的核心，简单来说，“认证”就是证明你是谁？ Web 应用程序一般做法通过表单提交用户名及密码达到认证目的。“授权”即是否允许已认证用户访问受保护资源。
参考文献：
http://kdboy.iteye.com/blog/1154644
http://www.ibm.com/developerworks/cn/java/j-lo-shiro/