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We ll include one general-purpose unchecked exception to denote a problem in executing the requested FTP command. Because this is a system-level problem from which a client typically cannot recover, it s not marked as @ApplicationException:
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public class FileTransferException extends RuntimeException{...}
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The bean implementation class will contain all of the business logic for our FTP client. The following imports are used:
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import import import import import import import import javax.annotation.PostConstruct; javax.annotation.PreDestroy; javax.annotation.Resource; javax.ejb.PostActivate; javax.ejb.PrePassivate; javax.ejb.Remote; javax.ejb.Remove; javax.ejb.Stateful;
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import org.apache.commons.net.ftp.FTPClient; import org.apache.commons.net.ftp.FTPFile; import org.apache.commons.net.ftp.FTPReply;
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The @PostConstruct and @PreDestroy annotations apply lifecycle callbacks when bean instances are created and destroyed, respectively. @PrePassivate and @PostActivate denote methods to be invoked during the stateful session passivation/activation phases.
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@Remove is not a callback, but rather marks that when the client invokes its method, the
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session should be retired. Finally, we ll use the Apache Commons FTP Client (http:// commons.apache.org/net/) to handle the finer points of the FTP protocol for us. First comes the bean declaration:
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@Stateful(name = FileTransferBean.EJB_NAME) @Remote(FileTransferRemoteBusiness.class) public class FileTransferBean implements FileTransferRemoteBusiness, Serializable { /** * Name of the EJB, used in Global JNDI addresses */ public static final String EJB_NAME = "FileTransferEJB";
Here we simply mark this class as a stateful session bean via the @Stateful annotation and assign it an explicit name such that we can construct the portable Global JNDI name in testing later. Also, we ll hardcode the host and port to be used in connecting to the FTP server. Typically this would be externalized, but for brevity s sake we ll keep things simple in this example:
/** * The name of the host to which we'll connect. * In production systems would typically be externalized * via configurable environment entry */ private static String CONNECT_HOST = "localhost"; /** * The port to which we'll connect. * In production systems would typically be externalized * via configurable environment entry. IANA standard * for FTP ports is 21, though this requires root access * on *nix for testing, so we'll use the nonstandard 12345. */ private static int CONNECT_PORT = 12345;
Next, we ll account for the instance members that will comprise our SFSB s internal state:
/** * The underlying FTP Client. We don't want its state * getting Serialized during passivation. We'll * reinitialize this client and its connections * upon activation. */ private FTPClient client; /** * Name of the present working directory. In cases where * we're passivated, if this is specified * we'll change into this directory upon activation. */ private String presentWorkingDirectory;
The client will be our delegate for all FTP operations. Because we cannot serialize it during passivation, we ll have to null this out during passivation and automatically reconnect upon activation. Although it may be possible to achieve the same goal implicitly using the Java transient keyword, the EJB specification advises against this because not all containers will rely upon Java Serialization for the passivation process. We ll also manually track the present working directory, our location within the FTP server, because once we go through the passivation/activation cycle we ll need to reconnect and move back to the same location. Our lifecycle callbacks will account for the operations that must take place during instance construction, passivation, activation, and session removal:
/** * Called by the container when the instance has been created or re-activated * (brought out of passivated state). Will construct the underlying FTP Client * and open all appropriate connections. * * @see FileTransferCommonBusiness#connect() */ @PostConstruct @PostActivate @Override public void connect() throws IllegalStateException, FileTransferException { /* * Precondition checks */ final FTPClient clientBefore = this.getClient(); if (clientBefore != null && clientBefore.isConnected()) { throw new IllegalStateException("FTP Client is already initialized"); } // Get the connection properties final String connectHost = this.getConnectHost(); final int connectPort = this.getConnectPort(); // Create the client final FTPClient client = new FTPClient(); // Connect Logic Here // Login Logic Here // Change into the Present Working Directory Logic Here }
The @PostConstruct and @PostActivate annotations denote to the server that it should call connect() after instance creation and activation (wakeup from passivation). Here we create a new client delegate, connect and log into the remote server, and finally switch into the present working directory (if we had one before passivation). After this
callback has been made, our SFSB instance and session has been initialized and is ready for service:
/** * Called by the container when the instance is about to be passivated or brought * out of service entirely. * * @see FileTransferCommonBusiness#disconnect() */ @PrePassivate @PreDestroy @Override public void disconnect() { // Obtain FTP Client final FTPClient client = this.getClient(); // If exists if (client != null) { // If connected if (client.isConnected()) { // Logout Logic Here } // Disconnect Logic Here
}
}
// Null out so we don't serialize this field this.client = null;
Due to the @PrePassivate and @PreDestroy annotations, the callback disconnect() is invoked by the container before passivation or the instance is removed from service. This is where we clean up any underlying resources by logging out and disconnecting from the FTP server. We have the expected accessor and mutator methods:
public public public public String getConnectHost() {// Logic here} void setConnectHost(final String connectHost) {// Logic here} int getConnectPort() {// Logic here} void setConnectPort(final int connectPort) {// Logic here}
Now all that s left is to do is implement the business interface methods that power the logic of the client. For brevity s sake, we ll omit the true code here; again, all of this is covered in the appendix:
/* (non-Javadoc) * @see FileTransferCommonBusiness#cd(java.lang.String) */ @Override public void cd(final String directory)
{ }
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