private void createUserDatabase() {// SimpleRealm.createUserDatabase() 创建了users 列表；User user1 = new User("ken", "blackcomb");user1.addRole("manager");user1.addRole("programmer");User user2 = new User("cindy", "bamboo");user2.addRole("programmer");users.add(user1);users.add(user2);}

public Principal authenticate (String username, String credentials); // generally used
public Principal authenticate (String username, byte[] credentials);
public Principal authenticate (String username, String digest, String nonce, String nc, String cnonce, String qop, String realm, String md5a2);
public Principal authenticate (X509Certificate cents[]);;

3）在catalina中， Realm接口的基本实现形式是org.apache.catalina.realm.RealmBase类；其UML类图如下：

public class GenericPrincipal implements Principal { //org.apache.catalina.realm.GenericPrincipal，代表一个用户（封装了username,password,role,realm）public GenericPrincipal(Realm realm, String name, String password) {this(realm, name, password, null);}public GenericPrincipal(Realm realm, String name, String password,List roles) {super();this.realm = realm;this.name = name;this.password = password;if (roles != null) {this.roles = new String[roles.size()];this.roles = (String[]) roles.toArray(this.roles);if (this.roles.length > 0)Arrays.sort(this.roles);}}protected String name = null;public String getName() {return (this.name);}protected String password = null; public String getPassword() {return (this.password);}protected Realm realm = null; public Realm getRealm() {return (this.realm);}protected String roles[] = new String[0]; public String[] getRoles() {return (this.roles);}public boolean hasRole(String role) {  // highlight line.if (role == null)return (false);return (Arrays.binarySearch(roles, role) >= 0);}public String toString() {StringBuffer sb = new StringBuffer("GenericPrincipal[");sb.append(this.name);sb.append("]");return (sb.toString());}
}

public final class LoginConfig { //org.apache.catalina.deploy.LoginConfigpublic LoginConfig() {super();}    public LoginConfig(String authMethod, String realmName,String loginPage, String errorPage) {super();setAuthMethod(authMethod);setRealmName(realmName);setLoginPage(loginPage);setErrorPage(errorPage);}// ------------------------------------------------------------- Properties   private String authMethod = null;public String getAuthMethod() {return (this.authMethod);}public void setAuthMethod(String authMethod) {this.authMethod = authMethod;}private String errorPage = null;public String getErrorPage() {return (this.errorPage);}public void setErrorPage(String errorPage) {        this.errorPage = RequestUtil.URLDecode(errorPage);}    private String loginPage = null;public String getLoginPage() {return (this.loginPage);}public void setLoginPage(String loginPage) {       this.loginPage = RequestUtil.URLDecode(loginPage);}    private String realmName = null;public String getRealmName() {return (this.realmName);}public void setRealmName(String realmName) {this.realmName = realmName;}   public String toString() {StringBuffer sb = new StringBuffer("LoginConfig[");sb.append("authMethod=");sb.append(authMethod);if (realmName != null) {sb.append(", realmName=");sb.append(realmName);}if (loginPage != null) {sb.append(", loginPage=");sb.append(loginPage);}if (errorPage != null) {sb.append(", errorPage=");sb.append(errorPage);}sb.append("]");return (sb.toString());}
}

public class BasicAuthenticator extends AuthenticatorBase {  <span style="font-family: SimSun;">//org.apache.catalina.authenticator.BasicAuthenticator，这里仅以BasicAuthenticator 为例po出 source code.</span>// ----------------------------------------------------- Instance Variables    protected static final Base64 base64Helper = new Base64();    protected static final String info ="org.apache.catalina.authenticator.BasicAuthenticator/1.0";   public String getInfo() {return (this.info);}public boolean authenticate(HttpRequest request,HttpResponse response,LoginConfig config)throws IOException {// Have we already authenticated someone?Principal principal =((HttpServletRequest) request.getRequest()).getUserPrincipal();String ssoId = (String) request.getNote(Constants.REQ_SSOID_NOTE);if (principal != null) {if (debug >= 1)log("Already authenticated '" + principal.getName() + "'");// Associate the session with any existing SSO sessionif (ssoId != null)associate(ssoId, getSession(request, true));return (true);}// Is there an SSO session against which we can try to reauthenticate?if (ssoId != null) {if (debug >= 1)log("SSO Id " + ssoId + " set; attempting reauthentication");           if (reauthenticateFromSSO(ssoId, request))return true;}// Validate any credentials already included with this requestHttpServletRequest hreq =(HttpServletRequest) request.getRequest();HttpServletResponse hres =(HttpServletResponse) response.getResponse();String authorization = request.getAuthorization();String username = parseUsername(authorization);String password = parsePassword(authorization);principal = context.getRealm().authenticate(username, password);if (principal != null) {register(request, response, principal, Constants.BASIC_METHOD,username, password);return (true);}// Send an "unauthorized" response and an appropriate challengeString realmName = config.getRealmName();if (realmName == null)realmName = hreq.getServerName() + ":" + hreq.getServerPort();    hres.setHeader("WWW-Authenticate","Basic realm=\"" + realmName + "\"");hres.setStatus(HttpServletResponse.SC_UNAUTHORIZED);//      hres.flushBuffer();return (false);}// ------------------------------------------------------ Protected Methodsprotected String parseUsername(String authorization) {if (authorization == null)return (null);if (!authorization.toLowerCase().startsWith("basic "))return (null);authorization = authorization.substring(6).trim();// Decode and parse the authorization credentialsString unencoded =new String(base64Helper.decode(authorization.getBytes()));int colon = unencoded.indexOf(':');if (colon < 0)return (null);String username = unencoded.substring(0, colon);//        String password = unencoded.substring(colon + 1).trim();return (username);}protected String parsePassword(String authorization) {if (authorization == null)return (null);if (!authorization.startsWith("Basic "))return (null);authorization = authorization.substring(6).trim();// Decode and parse the authorization credentialsString unencoded =new String(base64Helper.decode(authorization.getBytes()));int colon = unencoded.indexOf(':');if (colon < 0)return (null);//        String username = unencoded.substring(0, colon).trim();String password = unencoded.substring(colon + 1);return (password);}
}

// Identify the class name of the Valve we should configureString authenticatorName = "org.apache.catalina.authenticator.BasicAuthenticator";// Instantiate and install an Authenticator of the requested classValve authenticator = null;try {Class authenticatorClass = Class.forName(authenticatorName);authenticator = (Valve) authenticatorClass.newInstance();((StandardContext) context).addValve(authenticator);System.out.println("Added authenticator valve to Context");}catch (Throwable t) {}

public class SimpleRealm implements Realm {public SimpleRealm() {createUserDatabase(); //highlight line.}private void createUserDatabase() { // there are 2 roles.User user1 = new User("ken", "blackcomb");user1.addRole("manager"); // manager role.user1.addRole("programmer"); // programmer role.User user2 = new User("cindy", "bamboo");user2.addRole("programmer");users.add(user1);users.add(user2);// private ArrayList users = new ArrayList();}
}

public Principal authenticate(String username, String credentials) {System.out.println("SimpleRealm.authenticate()");if (username==null || credentials==null)return null;User user = getUser(username, credentials);if (user==null)return null;return new GenericPrincipal(this, user.username, user.password, user.getRoles()); // highlight line.}

public class GenericPrincipal implements Principal { // 该类封装了用户的一些信息，如username，pass，role，realm等info；public GenericPrincipal(Realm realm, String name, String password) { this(realm, name, password, null);}    public GenericPrincipal(Realm realm, String name, String password,List roles) {super();this.realm = realm;this.name = name;this.password = password;if (roles != null) {this.roles = new String[roles.size()];this.roles = (String[]) roles.toArray(this.roles);if (this.roles.length > 0)Arrays.sort(this.roles);}}protected String name = null;public String getName() {return (this.name);}protected String password = null;public String getPassword() {return (this.password);}protected Realm realm = null;public Realm getRealm() {return (this.realm);}protected String roles[] = new String[0];public String[] getRoles() {return (this.roles);}       public boolean hasRole(String role) {if (role == null)return (false);return (Arrays.binarySearch(roles, role) >= 0);}    public String toString() {StringBuffer sb = new StringBuffer("GenericPrincipal[");sb.append(this.name);sb.append("]");return (sb.toString());}
}

// tomcat-users.xml 的源码如下：
<?xml version='1.0' encoding='utf-8'?>
<tomcat-users><role rolename="tomcat"/><role rolename="role1"/><role rolename="manager"/><role rolename="admin"/><user username="tomcat" password="tomcat" roles="tomcat"/><user username="role1" password="tomcat" roles="role1"/><user username="both" password="tomcat" roles="tomcat,role1"/><user username="admin" password="admin" roles="admin,manager"/>
</tomcat-users>

// 以下代码是 Bootstrap2.java 中的源码Realm realm = new SimpleUserDatabaseRealm();String filedir = new File(System.getProperty("user.dir")).getParent() + File.separator +"conf" + File.separator + "tomcat-users.xml";((SimpleUserDatabaseRealm) realm).createDatabase(filedir); // highlight line.

public void createDatabase(String path) { //  SimpleUserDatabaseRealm.createDatabase().database = new MemoryUserDatabase(name);((MemoryUserDatabase) database).setPathname(path);try {database.open(); // highlight line.}catch (Exception e)  {}}

public void open() throws Exception { // org.apache.catalina.users.MemoryUserDatabase.open().synchronized (groups) {synchronized (users) {// Erase any previous groups and usersusers.clear();groups.clear();roles.clear();// Construct a reader for the XML input file (if it exists)File file = new File(pathname);if (!file.isAbsolute()) {file = new File(System.getProperty("catalina.base"),pathname);}if (!file.exists()) {return;}FileInputStream fis = new FileInputStream(file);// Construct a digester to read the XML input fileDigester digester = new Digester();digester.addFactoryCreate("tomcat-users/group",new MemoryGroupCreationFactory(this));digester.addFactoryCreate("tomcat-users/role",new MemoryRoleCreationFactory(this));digester.addFactoryCreate("tomcat-users/user",new MemoryUserCreationFactory(this));// Parse the XML input file to load this databasetry {digester.parse(fis);fis.close();} catch (Exception e) {try {fis.close();} catch (Throwable t) {;}throw e;}             }        }     }

public final class Bootstrap1 {public static void main(String[] args) {//invoke: http://localhost:8080/Modern or  http://localhost:8080/PrimitiveSystem.setProperty("catalina.base", System.getProperty("user.dir"));System.out.println("user.dir = " + System.getProperty("user.dir"));Connector connector = new HttpConnector();Wrapper wrapper1 = new SimpleWrapper();wrapper1.setName("Primitive");wrapper1.setServletClass("servlet.PrimitiveServlet");Wrapper wrapper2 = new SimpleWrapper();wrapper2.setName("Modern");wrapper2.setServletClass("servlet.ModernServlet");Context context = new StandardContext(); // highlight line.// StandardContext's start method adds a default mappercontext.setPath("/myApp");context.setDocBase("myApp");LifecycleListener listener = new SimpleContextConfig();// highlight line.((Lifecycle) context).addLifecycleListener(listener);context.addChild(wrapper1);context.addChild(wrapper2);// for simplicity, we don't add a valve, but you can add// valves to context or wrapper just as you did in Chapter 6Loader loader = new WebappLoader();context.setLoader(loader);// context.addServletMapping(pattern, name);context.addServletMapping("/Primitive", "Primitive");context.addServletMapping("/Modern", "Modern");// add ContextConfig. This listener is important because it configures// StandardContext (sets configured to true), otherwise StandardContext// won't start// add constraintSecurityCollection securityCollection = new SecurityCollection();// highlight line.securityCollection.addPattern("/");// highlight line.securityCollection.addMethod("GET");// highlight line.SecurityConstraint constraint = new SecurityConstraint();// highlight line.constraint.addCollection(securityCollection);// highlight line.constraint.addAuthRole("manager");// highlight line.LoginConfig loginConfig = new LoginConfig();// highlight line.loginConfig.setRealmName("Simple Realm");// add realmRealm realm = new SimpleRealm();// highlight line.context.setRealm(realm);// highlight line.context.addConstraint(constraint);// highlight line.context.setLoginConfig(loginConfig);// highlight line.connector.setContainer(context);// add a ManagerManager manager = new StandardManager();context.setManager(manager);try {connector.initialize();((Lifecycle) connector).start();((Lifecycle) context).start();// make the application wait until we press a key.System.in.read();((Lifecycle) context).stop();}catch (Exception e) {e.printStackTrace();}}
}

<pre name="code" class="java">E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\src>java -cp .;lib/servlet.jar;lib/catalina_4_1_24.jar;lib/catalina-5.5.4.jar;lib/naming-common
jar;lib/commons-collections.jar;lib/naming-resources.jar;lib/;lib/catalina.jar;E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\webroot com.tomc
t.chapter10.startup.Bootstrap1
HttpConnector Opening server socket on all host IP addresses
HttpConnector[8080] Starting background thread
WebappLoader[/myApp]: Deploying class repositories to work directory E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\src\work\_\_\myApp
Starting Wrapper Primitive
Starting Wrapper Modern
Added authenticator valve to Context
StandardManager[/myApp]: Seeding random number generator class java.security.SecureRandom
StandardManager[/myApp]: Seeding of random number generator has been completed
StandardManager[/myApp]: IOException while loading persisted sessions: java.io.EOFException
// 这是从文件中加载 session对象到内存，由于没有相关文件，所以加载失败，抛出异常，但这不会影响我们访问servlet，大家不要惊慌；
java.io.EOFExceptionat java.io.ObjectInputStream$PeekInputStream.readFully(Unknown Source)at java.io.ObjectInputStream$BlockDataInputStream.readShort(Unknown Source)at java.io.ObjectInputStream.readStreamHeader(Unknown Source)at java.io.ObjectInputStream.<init>(Unknown Source)at org.apache.catalina.util.CustomObjectInputStream.<init>(CustomObjectInputStream.java:103)at org.apache.catalina.session.StandardManager.load(StandardManager.java:408)at org.apache.catalina.session.StandardManager.start(StandardManager.java:655)at org.apache.catalina.core.StandardContext.start(StandardContext.java:3570)at com.tomcat.chapter10.startup.Bootstrap1.main(Bootstrap1.java:84)
StandardManager[/myApp]: Exception loading sessions from persistent storage
java.io.EOFExceptionat java.io.ObjectInputStream$PeekInputStream.readFully(Unknown Source)at java.io.ObjectInputStream$BlockDataInputStream.readShort(Unknown Source)at java.io.ObjectInputStream.readStreamHeader(Unknown Source)at java.io.ObjectInputStream.<init>(Unknown Source)at org.apache.catalina.util.CustomObjectInputStream.<init>(CustomObjectInputStream.java:103)at org.apache.catalina.session.StandardManager.load(StandardManager.java:408)at org.apache.catalina.session.StandardManager.start(StandardManager.java:655)at org.apache.catalina.core.StandardContext.start(StandardContext.java:3570)at com.tomcat.chapter10.startup.Bootstrap1.main(Bootstrap1.java:84)
SimpleRealm.authenticate()
SimpleRealm.authenticate()
ModernServlet -- init
SimpleRealm.authenticate()
SimpleRealm.authenticate()
SimpleRealm.authenticate()
SimpleRealm.authenticate()
SimpleRealm.authenticate()
SimpleRealm.authenticate()
init
SimpleRealm.authenticate()
from service
from service

public final class Bootstrap2 {public static void main(String[] args) {//invoke: http://localhost:8080/Modern or  http://localhost:8080/PrimitiveSystem.setProperty("catalina.base", System.getProperty("user.dir"));Connector connector = new HttpConnector();Wrapper wrapper1 = new SimpleWrapper();wrapper1.setName("Primitive");wrapper1.setServletClass("servlet.PrimitiveServlet");Wrapper wrapper2 = new SimpleWrapper();wrapper2.setName("Modern");wrapper2.setServletClass("servlet.ModernServlet");Context context = new StandardContext(); // highlight line.// StandardContext's start method adds a default mappercontext.setPath("/myApp");context.setDocBase("myApp");LifecycleListener listener = new SimpleContextConfig();// highlight line.((Lifecycle) context).addLifecycleListener(listener);context.addChild(wrapper1);context.addChild(wrapper2);// for simplicity, we don't add a valve, but you can add// valves to context or wrapper just as you did in Chapter 6Loader loader = new WebappLoader();context.setLoader(loader);// context.addServletMapping(pattern, name);context.addServletMapping("/Primitive", "Primitive");context.addServletMapping("/Modern", "Modern");// add ContextConfig. This listener is important because it configures// StandardContext (sets configured to true), otherwise StandardContext// won't start// add constraintSecurityCollection securityCollection = new SecurityCollection();// highlight line.securityCollection.addPattern("/");// highlight line.securityCollection.addMethod("GET");// highlight line.SecurityConstraint constraint = new SecurityConstraint();// highlight line.constraint.addCollection(securityCollection);// highlight line.constraint.addAuthRole("manager");// highlight line.constraint.addAuthRole("tomcat");// highlight line.注意这里的角色，必要要和tomcat-users.xml 中的users 列表相对应，如果要设置某个用户有权限访问servlet资源，则需要添加其所属的角色；LoginConfig loginConfig = new LoginConfig();// highlight line.loginConfig.setRealmName("Simple User Database Realm");// add realmRealm realm = new SimpleUserDatabaseRealm();// highlight line.String filedir = new File(System.getProperty("user.dir")).getParent() + File.separator + "conf" + File.separator + "tomcat-users.xml"; ((SimpleUserDatabaseRealm) realm).createDatabase(filedir); // highlight line.设置tomcat-users.xml 的文件路径 以载入其内容到内存进行身份验证工作；context.setRealm(realm);// highlight line.context.addConstraint(constraint);// highlight line.context.setLoginConfig(loginConfig);// highlight line.connector.setContainer(context);try {connector.initialize();((Lifecycle) connector).start();((Lifecycle) context).start();// make the application wait until we press a key.System.in.read();((Lifecycle) context).stop();}catch (Exception e) {e.printStackTrace();}}}

// tomcat-users.xml 的源码如下：
<?xml version='1.0' encoding='utf-8'?>
<tomcat-users><role rolename="tomcat"/><role rolename="role1"/><role rolename="manager"/><role rolename="admin"/><user username="tomcat" password="tomcat" roles="tomcat"/><user username="role1" password="tomcat" roles="role1"/><user username="both" password="tomcat" roles="tomcat,role1"/><user username="admin" password="admin" roles="admin,manager"/>
</tomcat-users>

E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\src>java -cp .;lib/servlet.jar;lib/catalina_4_1_24.jar;lib/catalina-5.5.4.jar;lib/naming-common.
jar;lib/commons-collections.jar;lib/naming-resources.jar;lib/;lib/catalina.jar;lib\commons-digester.jar;lib\commons-logging.jar;E:\bench-cluster\cloud
-data-preprocess\HowTomcatWorks\webroot com/tomcat/chapter10/startup/Bootstrap2
HttpConnector Opening server socket on all host IP addresses
HttpConnector[8080] Starting background thread
WebappLoader[/myApp]: Deploying class repositories to work directory E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\src\work\_\_\myApp
Starting Wrapper Primitive
Starting Wrapper Modern
Added authenticator valve to Context
StandardManager[/myApp]: Seeding random number generator class java.security.SecureRandom
StandardManager[/myApp]: Seeding of random number generator has been completed
StandardManager[/myApp]: IOException while loading persisted sessions: java.io.EOFException // 这是从文件中加载 session对象到内存，由于没有相关文件，所以加载失败，抛出异常，但这不会影响我们访问servlet，大家不要惊慌；
java.io.EOFExceptionat java.io.ObjectInputStream$PeekInputStream.readFully(Unknown Source)at java.io.ObjectInputStream$BlockDataInputStream.readShort(Unknown Source)at java.io.ObjectInputStream.readStreamHeader(Unknown Source)at java.io.ObjectInputStream.<init>(Unknown Source)at org.apache.catalina.util.CustomObjectInputStream.<init>(CustomObjectInputStream.java:103)at org.apache.catalina.session.StandardManager.load(StandardManager.java:408)at org.apache.catalina.session.StandardManager.start(StandardManager.java:655)at org.apache.catalina.core.StandardContext.start(StandardContext.java:3570)at com.tomcat.chapter10.startup.Bootstrap2.main(Bootstrap2.java:84)
StandardManager[/myApp]: Exception loading sessions from persistent storage
java.io.EOFException  at java.io.ObjectInputStream$PeekInputStream.readFully(Unknown Source)at java.io.ObjectInputStream$BlockDataInputStream.readShort(Unknown Source)at java.io.ObjectInputStream.readStreamHeader(Unknown Source)at java.io.ObjectInputStream.<init>(Unknown Source)at org.apache.catalina.util.CustomObjectInputStream.<init>(CustomObjectInputStream.java:103)at org.apache.catalina.session.StandardManager.load(StandardManager.java:408)at org.apache.catalina.session.StandardManager.start(StandardManager.java:655)at org.apache.catalina.core.StandardContext.start(StandardContext.java:3570)at com.tomcat.chapter10.startup.Bootstrap2.main(Bootstrap2.java:84)
ModernServlet -- init