異常流和程式流

研究了下Shiro的源碼，發現裡面用了大量的異常去控制程式流程。

下面以鑒權的流程為例，看一下鑒權的異常流和程式流

鑒權的方法，具體看注釋

//鑒權處理的方法，這個方法會将鑒權過程中出現的異常抛出來
protected abstract AuthenticationInfo doAuthenticate(AuthenticationToken token)
            throws AuthenticationException;      

已ModularRealmAuthenticator#doAuthenticate方法為例：

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);
        }
}

//單個realm的鑒權方法，鑒權過程中抛出多種異常
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;
}
      

下面看下doAuthenticate的調用者是怎麼處理doAuthenticate抛出的異常的：

public final AuthenticationInfo authenticate(AuthenticationToken token) throws AuthenticationException {
        //參數異常
        if (token == null) {
            throw new IllegalArgumentException("Method argumet (authentication token) cannot be null.");
        }

        log.trace("Authentication attempt received for token [{}]", token);

        AuthenticationInfo info;
        try {
            //doAuthenticate方法的定義看下面，他會在鑒權的過程中抛出鑒權失敗的異常AuthenticationException。本方法會處理此異常，包裝并給其添加更詳細的異常資訊，然後再将此異常抛出給上一層調用者。
            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) {
            //處理此異常，處理的過程就是包裝并給其添加更詳細的異常資訊，然後再将此異常抛出給上一層調用者。
            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);
                }
            }

            //把包裝後的異常抛出
            throw ae;
        }

        log.debug("Authentication successful for token [{}].  Returned account [{}]", token, info);

        notifySuccess(token, info);

        return info;
    }      

主要是将doAuthenticate抛出的異常包裝處理了一下。

authenticate方法的調用者将錯誤直接抛出：

public AuthenticationInfo authenticate(AuthenticationToken token) throws AuthenticationException {
        return this.authenticator.authenticate(token);
    }      

上面的authenticate方法的調用者。

DefaultSecurityManager#login

public Subject login(Subject subject, AuthenticationToken token) throws AuthenticationException {
        AuthenticationInfo info;
        try {
            info = authenticate(token);
        } catch (AuthenticationException ae) {
            //處理authenticate方法抛出的異常
            try {
                onFailedLogin(token, ae, subject);
            } catch (Exception e) {
                //處理onFailedLogin方法抛出的異常，處理完了之後，再抛出去
                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;
    }      

DelegatingSubject#login

//securityManager.login方法抛出的異常直接在抛出去。
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();
        }
        //抛異常給上層調用者
        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;
        }
    }