JavaMail中UIDFolder是interface，Folder是抽象类，都没有实现getMessagesByUID()，怎么用UID取Message?

Question

研究这个类看看package javax.mail;import com.sun.mail.util.LineInputStream;
import java.io.*;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.net.InetAddress;
import java.net.URL;
import java.util.*;// Referenced classes of package javax.mail:
//            Address, Authenticator, MessagingException, NoSuchProviderException, 
//            PasswordAuthentication, Provider, Service, Store, 
//            Transport, URLName, Folderpublic final class Session
{    private Session(Properties properties, Authenticator authenticator1)
    {
        authTable = new Hashtable();
        debug = false;
        providers = new Vector();
        providersByProtocol = new Hashtable();
        providersByClassName = new Hashtable();
        addressMap = new Properties();
        props = properties;
        authenticator = authenticator1;
        if(Boolean.valueOf(properties.getProperty("mail.debug")).booleanValue())
            debug = true;
        Class class1;
        if(authenticator1 != null)
            class1 = authenticator1.getClass();
        else
            class1 = getClass();
        loadProviders(class1);
        loadAddressMap(class1);
    }    public static Session getInstance(Properties properties, Authenticator authenticator1)
    {
        return new Session(properties, authenticator1);
    }    public static Session getInstance(Properties properties)
    {
        return new Session(properties, null);
    }    public static Session getDefaultInstance(Properties properties, Authenticator authenticator1)
    {
        if(defaultSession == null)
            defaultSession = new Session(properties, authenticator1);
        else
        if(defaultSession.authenticator != authenticator1 && (defaultSession.authenticator == null || authenticator1 == null || defaultSession.authenticator.getClass().getClassLoader() != authenticator1.getClass().getClassLoader()))
            throw new SecurityException("Access to default session denied");
        return defaultSession;
    }    public static Session getDefaultInstance(Properties properties)
    {
        return getDefaultInstance(properties, null);
    }    public void setDebug(boolean flag)
    {
        debug = flag;
    }    public boolean getDebug()
    {
        return debug;
    }    public Provider[] getProviders()
    {
        Provider aprovider[] = new Provider[providers.size()];
        providers.copyInto(aprovider);
        return aprovider;
    }    public Provider getProvider(String s)
        throws NoSuchProviderException
    {
        if(s == null || s.length() <= 0)
            throw new NoSuchProviderException("Invalid protocol: null");
        Provider provider = null;
        String s1 = props.getProperty("mail." + s + ".class");
        if(s1 != null)
        {
            if(debug)
                System.out.println("DEBUG: mail." + s + ".class property exists and points to " + s1);
            provider = (Provider)providersByClassName.get(s1);
        }
        if(provider != null)
            return provider;
        provider = (Provider)providersByProtocol.get(s);
        if(provider == null)
            throw new NoSuchProviderException("No provider for " + s);
        if(debug)
            System.out.println("\nDEBUG: getProvider() returning " + provider.toString());
        return provider;
    }    public void setProvider(Provider provider)
        throws NoSuchProviderException
    {
        if(provider == null)
        {
            throw new NoSuchProviderException("Can't set null provider");
        }
        else
        {
            providersByProtocol.put(provider.getProtocol(), provider);
            props.put("mail." + provider.getProtocol() + ".class", provider.getClassName());
            return;
        }
    }    public Store getStore()
        throws NoSuchProviderException
    {
        return getStore(getProperty("mail.store.protocol"));
    }    public Store getStore(String s)
        throws NoSuchProviderException
    {
        return getStore(new URLName(s, null, -1, null, null, null));
    }    public Store getStore(URLName urlname)
        throws NoSuchProviderException
    {
        String s = urlname.getProtocol();
        Provider provider = getProvider(s);
        return getStore(provider, urlname);
    }    public Store getStore(Provider provider)
        throws NoSuchProviderException
    {
        return getStore(provider, null);
    }    private Store getStore(Provider provider, URLName urlname)
        throws NoSuchProviderException
    {
        if(provider == null || provider.getType() != Provider.Type.STORE)
            throw new NoSuchProviderException("invalid provider");
        try
        {
            return (Store)getService(provider, urlname);
        }
        catch(ClassCastException ex)
        {
            throw new NoSuchProviderException("incorrect class");
        }
    }    public Folder getFolder(URLName urlname)
        throws MessagingException
    {
        Store store = getStore(urlname);
        store.connect();
        return store.getFolder(urlname);
    }    public Transport getTransport()
        throws NoSuchProviderException
    {
        return getTransport(getProperty("mail.transport.protocol"));
    }    public Transport getTransport(String s)
        throws NoSuchProviderException
    {
        return getTransport(new URLName(s, null, -1, null, null, null));
    }    public Transport getTransport(URLName urlname)
        throws NoSuchProviderException
    {
        String s = urlname.getProtocol();
        Provider provider = getProvider(s);
        return getTransport(provider, urlname);
    }    public Transport getTransport(Provider provider)
        throws NoSuchProviderException
    {
        return getTransport(provider, null);
    }    public Transport getTransport(Address address)
        throws NoSuchProviderException
    {
        String s = (String)addressMap.get(address.getType());
        if(s == null)
            throw new NoSuchProviderException("No provider for Address type: " + address.getType());
        else
            return getTransport(s);
    }    private Transport getTransport(Provider provider, URLName urlname)
        throws NoSuchProviderException
    {
        if(provider == null || provider.getType() != Provider.Type.TRANSPORT)
            throw new NoSuchProviderException("invalid provider");
        try
        {
            return (Transport)getService(provider, urlname);
        }
        catch(ClassCastException ex)
        {
            throw new NoSuchProviderException("incorrect class");
        }
    }    private Object getService(Provider provider, URLName urlname)
        throws NoSuchProviderException
    {
        if(provider == null)
            throw new NoSuchProviderException("null");
        if(urlname == null)
            urlname = new URLName(provider.getProtocol(), null, -1, null, null, null);
        Object obj = null;
        ClassLoader classloader;
        if(authenticator != null)
            classloader = authenticator.getClass().getClassLoader();
        else
            classloader = getClass().getClassLoader();
        Class class1 = null;
        try
        {
            class1 = classloader.loadClass(provider.getClassName());
        }
        catch(Exception ex)
        {
            try
            {
                class1 = Class.forName(provider.getClassName());
            }
            catch(Exception exception)
            {
                if(debug)
                    exception.printStackTrace();
                throw new NoSuchProviderException(provider.getProtocol());
            }
        }
        try
        {
            Class aclass[] = {
                class$javax$mail$Session == null ? (class$javax$mail$Session = class$("javax.mail.Session")) : class$javax$mail$Session, class$javax$mail$URLName == null ? (class$javax$mail$URLName = class$("javax.mail.URLName")) : class$javax$mail$URLName
            };
            Constructor constructor = class1.getConstructor(aclass);
            Object aobj[] = {
                this, urlname
            };
            obj = constructor.newInstance(aobj);
        }
        catch(Exception exception1)
        {
            if(debug)
                exception1.printStackTrace();
            throw new NoSuchProviderException(provider.getProtocol());
        }
        return obj;
    }    public void setPasswordAuthentication(URLName urlname, PasswordAuthentication passwordauthentication)
    {
        if(passwordauthentication == null)
        {
            authTable.remove(urlname);
            return;
        }
        else
        {
            authTable.put(urlname, passwordauthentication);
            return;
        }
    }    public PasswordAuthentication getPasswordAuthentication(URLName urlname)
    {
        return (PasswordAuthentication)authTable.get(urlname);
    }    public PasswordAuthentication requestPasswordAuthentication(InetAddress inetaddress, int i, String s, String s1, String s2)
    {
        if(authenticator != null)
            return authenticator.requestPasswordAuthentication(inetaddress, i, s, s1, s2);
        else
            return null;
    }    public Properties getProperties()
    {
        return props;
    }    public String getProperty(String s)
    {
        return props.getProperty(s);
    }    private void loadProviders(Class class1)
    {
        Object obj = null;
        try
        {
            String s = System.getProperty("java.home") + File.separator + "lib" + File.separator + "javamail.providers";
            BufferedInputStream bufferedinputstream = new BufferedInputStream(new FileInputStream(s));
            if(bufferedinputstream != null)
            {
                loadProvidersFromStream(bufferedinputstream);
                bufferedinputstream.close();
                if(debug)
                    pr("DEBUG: loaded providers in <java.home>/lib");
            }
            else
            if(debug)
                pr("DEBUG: not loading system providers in <java.home>/lib");
        }
        catch(FileNotFoundException ex)
        {
            if(debug)
                pr("DEBUG: not loading system providers in <java.home>/lib");
        }
        catch(IOException ioexception)
        {
            if(debug)
                pr("DEBUG: " + ioexception.getMessage());
        }
        catch(SecurityException ex)
        {
            if(debug)
                pr("DEBUG: not loading system providers in <java.home>/lib");
        }
        Object obj1 = null;
        String s1 = "META-INF/javamail.providers";
        String s2 = "/" + s1;
        boolean flag = false;
        if(getResources != null)
            try
            {
                ClassLoader classloader = class1.getClassLoader();
                Enumeration enumeration;
                if(classloader != null)
                    enumeration = (Enumeration)getResources.invoke(classloader, new String[] {
                        s1
                    });
                else
                    enumeration = (Enumeration)getSystemResources.invoke(classloader, new String[] {
                        s1
                    });
                while(enumeration.hasMoreElements()) 
                {
                    URL url = (URL)enumeration.nextElement();
                    InputStream inputstream = url.openStream();
                    if(inputstream != null)
                        try
                        {
                            loadProvidersFromStream(inputstream);
                            flag = true;
                            inputstream.close();
                            if(debug)
                                pr("DEBUG: successfully loaded optional custom providers from URL: " + url);
                        }
                        catch(IOException ioexception3)
                        {
                            if(debug)
                                pr("DEBUG: " + ioexception3.getMessage());
                        }
                    else
                    if(debug)
                        pr("DEBUG: not loading optional custom providers from URL: " + url);
                }            }
            catch(Exception exception)
            {
                if(debug)
                    pr("DEBUG: " + exception);
            }
        if(!flag)
        {
            InputStream inputstream1 = class1.getResourceAsStream(s2);
            if(inputstream1 != null)
                try
                {
                    loadProvidersFromStream(inputstream1);
                    inputstream1.close();
                    if(debug)
                        pr("DEBUG: successfully loaded optional custom providers: " + s2);
                }
                catch(IOException ioexception1)
                {
                    if(debug)
                        pr("DEBUG: " + ioexception1);
                }
            else
            if(debug)
                pr("DEBUG: not loading optional custom providers file: " + s2);
        }
        InputStream inputstream2 = null;
        String s3 = "/META-INF/javamail.default.providers";
        inputstream2 = class1.getResourceAsStream(s3);
        if(inputstream2 != null)
            try
            {
                loadProvidersFromStream(inputstream2);
                inputstream2.close();
                if(debug)
                    pr("DEBUG: successfully loaded default providers");
            }
            catch(IOException ioexception2)
            {
                if(debug)
                    pr("DEBUG: " + ioexception2.getMessage());
            }
        else
        if(debug)
            pr("DEBUG: can't load default providers file" + s3);
        if(debug)
        {
            System.out.println("\nDEBUG: Tables of loaded providers");
            pr("DEBUG: Providers Listed By Class Name: " + providersByClassName.toString());
            pr("DEBUG: Providers Listed By Protocol: " + providersByProtocol.toString());
        }
    }    private void loadProvidersFromStream(InputStream inputstream)
        throws IOException
    {
        if(inputstream != null)
        {
            LineInputStream lineinputstream = new LineInputStream(inputstream);
            String s;
            while((s = lineinputstream.readLine()) != null) 
                if(!s.startsWith("#"))
                {
                    Provider.Type type = null;
                    String s1 = null;
                    String s2 = null;
                    String s3 = null;
                    String s4 = null;
                    for(StringTokenizer stringtokenizer = new StringTokenizer(s, ";"); stringtokenizer.hasMoreTokens();)
                    {
                        String s5 = stringtokenizer.nextToken().trim();
                        int i = s5.indexOf("=");
                        if(s5.startsWith("protocol="))
                            s1 = s5.substring(i + 1);
                        else
                        if(s5.startsWith("type="))
                        {
                            String s6 = s5.substring(i + 1);
                            if(s6.equalsIgnoreCase("store"))
                                type = Provider.Type.STORE;
                            else
                            if(s6.equalsIgnoreCase("transport"))
                                type = Provider.Type.TRANSPORT;
                        }
                        else
                        if(s5.startsWith("class="))
                            s2 = s5.substring(i + 1);
                        else
                        if(s5.startsWith("vendor="))
                            s3 = s5.substring(i + 1);
                        else
                        if(s5.startsWith("version="))
                            s4 = s5.substring(i + 1);
                    }                    if(type == null || s1 == null || s2 == null || s1.length() <= 0 || s2.length() <= 0)
                    {
                        if(debug)
                            System.out.println("DEBUG: Bad provider entry: " + s);
                    }
                    else
                    {
                        Provider provider = new Provider(type, s1, s2, s3, s4);
                        providers.addElement(provider);
                        providersByClassName.put(s2, provider);
                        if(!providersByProtocol.containsKey(s1))
                            providersByProtocol.put(s1, provider);
                    }
                }        }
    }    private void loadAddressMap(Class class1)
    {
        InputStream inputstream = null;
        String s = "/META-INF/javamail.default.address.map";
        inputstream = class1.getResourceAsStream(s);
        if(inputstream != null)
            try
            {
                addressMap.load(inputstream);
                inputstream.close();
            }
            catch(IOException ex) {}
            catch(SecurityException ex) {}
        Object obj = null;
        String s1 = "META-INF/javamail.address.map";
        String s2 = "/" + s1;
        boolean flag = false;
        if(getResources != null)
            try
            {
                ClassLoader classloader = class1.getClassLoader();
                Enumeration enumeration;
                if(classloader != null)
                    enumeration = (Enumeration)getResources.invoke(classloader, new String[] {
                        s1
                    });
                else
                    enumeration = (Enumeration)getSystemResources.invoke(classloader, new String[] {
                        s1
                    });
                while(enumeration.hasMoreElements()) 
                {
                    URL url = (URL)enumeration.nextElement();
                    InputStream inputstream1 = url.openStream();
                    if(inputstream1 != null)
                        try
                        {
                            addressMap.load(inputstream1);
                            flag = true;
                            inputstream1.close();
                            if(debug)
                                pr("DEBUG: successfully loaded optional address map from URL: " + url);
                        }
                        catch(IOException ioexception1)
                        {
                            if(debug)
                                pr("DEBUG: " + ioexception1.getMessage());
                        }
                    else
                    if(debug)
                        pr("DEBUG: not loading optional address map from URL: " + url);
                }            }
            catch(Exception exception)
            {
                if(debug)
                    pr("DEBUG: " + exception);
            }
        if(!flag)
        {
            InputStream inputstream2 = class1.getResourceAsStream(s2);
            if(inputstream2 != null)
                try
                {
                    addressMap.load(inputstream2);
                    inputstream2.close();
                    if(debug)
                        pr("DEBUG: successfully loaded optional address map: " + s2);
                }
                catch(IOException ioexception)
                {
                    if(debug)
                        pr("DEBUG: " + ioexception);
                }
            else
            if(debug)
                pr("DEBUG: not loading optional address map file: " + s2);
        }
        BufferedInputStream bufferedinputstream = null;
        try
        {
            String s3 = System.getProperty("java.home") + File.separator + "lib" + File.separator + "javamail.address.map";
            bufferedinputstream = new BufferedInputStream(new FileInputStream(s3));
        }
        catch(FileNotFoundException ex) {}
        catch(SecurityException ex) {}
        if(bufferedinputstream != null)
            try
            {
                addressMap.load(bufferedinputstream);
                bufferedinputstream.close();
                return;
            }
            catch(IOException ex)
            {
                return;
            }
        else
            return;
    }    private static void pr(String s)
    {
        System.out.println(s);
    }    static Class class$(String s)
    {
        try
        {
            return Class.forName(s);
        }
        catch(ClassNotFoundException classnotfoundexception)
        {
            throw new NoClassDefFoundError(classnotfoundexception.getMessage());
        }
    }    private Properties props;
    private Authenticator authenticator;
    private Hashtable authTable;
    private boolean debug;
    private Vector providers;
    private Hashtable providersByProtocol;
    private Hashtable providersByClassName;
    private Properties addressMap;
    private static Method getResources = null;
    private static Method getSystemResources = null;
    private static Session defaultSession = null;
    static Class class$java$lang$ClassLoader; /* synthetic field */
    static Class class$java$lang$String; /* synthetic field */
    static Class class$javax$mail$Session; /* synthetic field */
    static Class class$javax$mail$URLName; /* synthetic field */    static 
    {
        try
        {
            Class class1 = class$java$lang$ClassLoader == null ? (class$java$lang$ClassLoader = class$("java.lang.ClassLoader")) : class$java$lang$ClassLoader;
            getResources = class1.getMethod("getResources", new Class[] {
                class$java$lang$String == null ? (class$java$lang$String = class$("java.lang.String")) : class$java$lang$String
            });
            getSystemResources = class1.getMethod("getSystemResources", new Class[] {
                class$java$lang$String == null ? (class$java$lang$String = class$("java.lang.String")) : class$java$lang$String
            });
        }
        catch(Throwable ex) {}
    }
}

Answer 1

package com.sun.mail.pop3;import java.io.EOFException;
import java.io.IOException;
import java.lang.reflect.Constructor;
import java.util.Vector;
import javax.mail.*;
import javax.mail.event.ConnectionEvent;
import javax.mail.internet.MimeMessage;// Referenced classes of package com.sun.mail.pop3:
//            DefaultFolder, POP3Message, POP3Store, Protocol, 
//            Statuspublic class POP3Folder extends Folder
{    POP3Folder(POP3Store pop3store, String s)
    {
        super(pop3store);
        exists = false;
        opened = false;
        doneUidl = false;
        name = s;
        if(s.equalsIgnoreCase("INBOX"))
            exists = true;
    }    public String getName()
    {
        return name;
    }    public String getFullName()
    {
        return name;
    }    public Folder getParent()
    {
        return new DefaultFolder((POP3Store)store);
    }    public boolean exists()
    {
        return exists;
    }    public Folder[] list(String s)
        throws MessagingException
    {
        throw new MessagingException("not a directory");
    }    public char getSeparator()
    {
        return 0;
    }    public int getType()
    {
        return 1;
    }    public boolean create(int i)
        throws MessagingException
    {
        return false;
    }    public boolean hasNewMessages()
        throws MessagingException
    {
        return false;
    }    public Folder getFolder(String s)
        throws MessagingException
    {
        throw new MessagingException("not a directory");
    }    public boolean delete(boolean flag)
        throws MessagingException
    {
        throw new MethodNotSupportedException("delete");
    }    public boolean renameTo(Folder folder)
        throws MessagingException
    {
        throw new MethodNotSupportedException("renameTo");
    }    public synchronized void open(int i)
        throws MessagingException
    {
        checkClosed();
        if(!exists)
            throw new FolderNotFoundException(this, "folder is not INBOX");
        try
        {
            port = ((POP3Store)store).getPort(this);
            mode = i;
            opened = true;
            total = port.stat().total;
        }
        catch(IOException ioexception)
        {
            throw new MessagingException("Open failed", ioexception);
        }
        message_cache = new Vector(total);
        message_cache.setSize(total);
        doneUidl = false;
        notifyConnectionListeners(1);
    }    public synchronized void close(boolean flag)
        throws MessagingException
    {
        checkOpen();
        try
        {
            if(((POP3Store)store).rsetBeforeQuit)
                port.rset();
            if(flag && mode == 2)
            {
                for(int i = 0; i < message_cache.size(); i++)
                {
                    POP3Message pop3message;
                    if((pop3message = (POP3Message)message_cache.elementAt(i)) != null && pop3message.isSet(javax.mail.Flags.Flag.DELETED))
                        try
                        {
                            port.dele(i + 1);
                        }
                        catch(IOException ex)
                        {
                            throw new MessagingException();
                        }
                }            }
            port.quit();
        }
        catch(IOException ex) {}
        finally
        {
            port = null;
            ((POP3Store)store).closePort(this);
            message_cache = null;
            opened = false;
            notifyConnectionListeners(3);
        }
    }    public boolean isOpen()
    {
        return opened;
    }    public Flags getPermanentFlags()
    {
        return new Flags();
    }    public int getMessageCount()
        throws MessagingException
    {
        if(!opened)
        {
            return -1;
        }
        else
        {
            checkReadable();
            return total;
        }
    }    public synchronized Message getMessage(int i)
        throws MessagingException
    {
        checkOpen();
        POP3Message pop3message;
        if((pop3message = (POP3Message)message_cache.elementAt(i - 1)) == null)
        {
            pop3message = createMessage(this, i);
            message_cache.setElementAt(pop3message, i - 1);
        }
        return pop3message;
    }    protected POP3Message createMessage(Folder folder, int i)
        throws MessagingException
    {
        POP3Message pop3message = null;
        Constructor constructor = ((POP3Store)store).messageConstructor;
        if(constructor != null)
            try
            {
                Object aobj[] = {
                    this, new Integer(i)
                };
                pop3message = (POP3Message)constructor.newInstance(aobj);
            }
            catch(Exception ex) {}
        if(pop3message == null)
            pop3message = new POP3Message(this, i);
        return pop3message;
    }    public void appendMessages(Message amessage[])
        throws MessagingException
    {
        throw new MethodNotSupportedException("Append not supported");
    }    public Message[] expunge()
        throws MessagingException
    {
        throw new MethodNotSupportedException("Expunge not supported");
    }    public synchronized void fetch(Message amessage[], FetchProfile fetchprofile)
        throws MessagingException
    {
        checkReadable();
        if(!doneUidl && fetchprofile.contains(javax.mail.UIDFolder.FetchProfileItem.UID))
        {
            String as[] = new String[message_cache.size()];
            try
            {
                if(!port.uidl(as))
                    return;
            }
            catch(EOFException eofexception)
            {
                close(false);
                throw new FolderClosedException(this, eofexception.toString());
            }
            catch(IOException ioexception)
            {
                throw new MessagingException("error getting UIDL", ioexception);
            }
            for(int j = 0; j < as.length; j++)
                if(as[j] != null)
                {
                    POP3Message pop3message1 = (POP3Message)getMessage(j + 1);
                    pop3message1.uid = as[j];
                }            doneUidl = true;
        }
        if(fetchprofile.contains(javax.mail.FetchProfile.Item.ENVELOPE))
        {
            for(int i = 0; i < amessage.length; i++)
            {
                POP3Message pop3message = (POP3Message)amessage[i];
                pop3message.getHeader("");
                pop3message.getSize();
            }        }
    }    public synchronized String getUID(Message message)
        throws MessagingException
    {
        checkOpen();
        POP3Message pop3message = (POP3Message)message;
        try
        {
            if(pop3message.uid == "UNKNOWN")
                pop3message.uid = port.uidl(pop3message.getMessageNumber());
            return pop3message.uid;
        }
        catch(EOFException eofexception)
        {
            close(false);
            throw new FolderClosedException(this, eofexception.toString());
        }
        catch(IOException ioexception)
        {
            throw new MessagingException("error getting UIDL", ioexception);
        }
    }    protected void finalize()
        throws Throwable
    {
        close(false);
    }    void checkOpen()
        throws IllegalStateException
    {
        if(!opened)
            throw new IllegalStateException("Folder is not Open");
        else
            return;
    }    void checkClosed()
        throws IllegalStateException
    {
        if(opened)
            throw new IllegalStateException("Folder is Open");
        else
            return;
    }    void checkReadable()
        throws IllegalStateException
    {
        if(!opened || mode != 1 && mode != 2)
            throw new IllegalStateException("Folder is not Readable");
        else
            return;
    }    void checkWritable()
        throws IllegalStateException
    {
        if(!opened || mode != 2)
            throw new IllegalStateException("Folder is not Writable");
        else
            return;
    }    Protocol getProtocol()
        throws MessagingException
    {
        checkOpen();
        return port;
    }    protected void notifyMessageChangedListeners(int i, Message message)
    {
        super.notifyMessageChangedListeners(i, message);
    }    private String name;
    private Protocol port;
    private int total;
    private boolean exists;
    private boolean opened;
    private Vector message_cache;
    private boolean doneUidl;
}

Answer 2

小弟资质较浅，看不出和uid有什么关系，请指教

Answer 3

1>uidmsgshow.java Folder folder = store.getDefaultFolder();
2>Session.java
    public Store getStore(URLName urlname)
        throws NoSuchProviderException
    {
        String s = urlname.getProtocol();
        Provider provider = getProvider(s);
        return getStore(provider, urlname);
    }
    public Provider getProvider(String s)
        throws NoSuchProviderException
    {
        if(s == null || s.length() <= 0)
            throw new NoSuchProviderException("Invalid protocol: null");
        Provider provider = null;
        String s1 = props.getProperty("mail." + s + ".class");
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        if(s1 != null)
        {
            if(debug)
                System.out.println("DEBUG: mail." + s + ".class property exists and points to " + s1);
            provider = (Provider)providersByClassName.get(s1);
        }
        if(provider != null)
            return provider;
        provider = (Provider)providersByProtocol.get(s);
        if(provider == null)
            throw new NoSuchProviderException("No provider for " + s);
        if(debug)
            System.out.println("\nDEBUG: getProvider() returning " + provider.toString());
        return provider;
    }