home | O'Reilly's CD bookshelfs | FreeBSD | Linux | Cisco | Cisco Exam    

Book Home Java Servlet Programming Search this book

Appendix A. Servlet API Quick Reference

The javax.servlet package is the core of the Servlet API. It includes the basic Servlet interface, which all servlets must implement in one form or another, and an abstract GenericServlet class for developing basic servlets. This package also includes classes for communication with the host server and client (ServletRequest and ServletResponse) and communicating with the client (ServletInputStream and ServletOutputStream). The class hierarchy of the javax.servlet package is shown in Figure A-1. Servlets should confine themselves to the classes in this package in situations where the underlying protocol is unknown.

figure

Figure A-1. The javax.servlet package

GenericServlet

Synopsis

Class Name: javax.servlet.GenericServlet
Superclass: java.lang.Object
Immediate Subclassesjavax.servlet.http.HttpServlet
Interfaces Implemented:javax.servlet.Servletjavax.servlet.ServletConfigjava.io.Serializable
Availability: Servlet API 1.0 and later

Description

GenericServlet provides a basic implementation of the Servlet interface for protocol-independent servlets. As a convenience, it also implements the ServletConfig interface. Most servlet developers subclass this class or HttpServlet, rather than implement the Servlet interface directly.

GenericServlet includes basic versions of the init() and destroy() methods, which perform basic setup and cleanup tasks, such as managing the server's ServletConfig object. It's good form for a servlet that overrides one of these methods to call the superclass version of the method. GenericServlet also includes a log() method that provides easy access to the logging functions from ServletContext.

The service() method is declared as abstract and must be overridden. Well written servlets also override getServletInfo().

Class Summary

public abstract class GenericServlet
 implements Servlet, ServletConfig, java.io.Serializable {
  // Constructors
  public GenericServlet();

  // Instance Methods
  public void destroy();
  public String getInitParameter(String name);
  public Enumeration getInitParameterNames();
  public ServletConfig getServletConfig();
  public ServletContext getServletContext();
  public String getServletInfo();
  public void init(ServletConfig config) throws ServletException;
  public void log(String msg);
  public abstract void service(ServletRequest req, ServletResponse res)
    throws ServletException, IOException;
}

Constructors

GenericServlet()

public GenericServlet()
Description
The default GenericServlet constructor does no work. Any servlet initialization tasks should be performed in init(), rather than in the constructor.

Instance Methods

destroy()

public void destroy()
Description
Called by the server before unloading the servlet. The default implementation logs the servlet's destruction in the server log file using the log() method. A servlet can override this method to save its state, free its resources, etc.

getInitParameter()

public String getInitParameter(String name)
Description
Returns the value of the named servlet initialization parameter or null if no matching parameter is found. From the ServletConfig interface.

getInitParameterNames()

public Enumeration getInitParameterNames()
Description
Returns all the servlet's init parameter names as an Enumeration of String objects or an empty Enumeration if no parameters exist. From the ServletConfig interface.

getServletConfig()

public ServletConfig getServletConfig()
Description
Returns the servlet's ServletConfig object. In practice, this method is rarely called by a GenericServlet because all of the ServletConfig methods are duplicated internally.

getServletContext()

public ServletContext getServletContext()
Description
Returns the servlet's ServletContext object. From the ServletConfig interface.

getServletInfo()

public String getServletInfo()
Description
Returns a programmer-defined String that describes the servlet. A servlet should override this method and provide a customized identity string (e.g., "Al's Message Board Servlet v1.21"), but it is not required.

init()

public void init(ServletConfig config) throws ServletException
Description
Called by the server after the servlet is first loaded and before the servlet's service() method is called. The default implementation of init() logs the servlet's initialization and stores the ServletConfig object for use by the methods in the ServletConfig interface. A servlet can override this method to perform additional one-time setup, creation of resources, etc. A servlet should always call the superclass implementation of init() using super.init(config) before executing any custom initialization code.

log()

public void log(String msg)
Description
Writes the given message to a servlet log, usually an event log file. Both the output format and location are server-specific.

service()

public abstract void service(ServletRequest req, ServletResponse res)
  throws ServletException, IOException
Description
Called to handle a single client request. A servlet receives request information via a ServletRequest object and sends data back to the client via a ServletResponse object. This is the only method that must be overridden when extending GenericServlet. Because multiple service requests may execute concurrently, the service() method must be thread safe, unless the servlet also implements the SingleThreadModel interface.
Servlet

Synopsis

Interface Name: javax.servlet.Servlet
Super-interface: None
Immediate Subinterfaces: None
Implemented By: javax.servlet.GenericServlet
Availability: Servlet API 1.0 and later

Description

All servlets implement the Servlet interface, either directly or by subclassing the GenericServlet or HttpServlet class. Most servlet developers find it easier to subclass one of the two existing servlet classes than to implement this interface directly. The interface declares the basic servlet functionality--initializing a servlet, handling a client request, and destroying a servlet.

Interface Declaration

public interface Servlet {
  // Methods
  public abstract void destroy();
  public abstract ServletConfig getServletConfig();
  public abstract String getServletInfo();
  public abstract void init(ServletConfig config) throws ServletException;
  public abstract void service(ServletRequest req, ServletResponse res)
    throws ServletException, IOException;
}

Methods

destroy()

public abstract void destroy()
Description
Called when the server is preparing to unload a servlet. Used to clean up any outstanding resources (database connections, threads, file handles and so forth). The servlet programmer is responsible for making sure that any requests currently executing are allowed to finish.

getServletConfig()

public abstract ServletConfig getServletConfig()
Description
Returns the ServletConfig object passed to the init() method.

getServletInfo()

public abstract String getServletInfo()
Description
Returns a programmer-defined String that describes the servlet.

init()

public abstract void init(ServletConfig config) throws ServletException
Description
Called by the server when the servlet is first loaded. The init() method should store the ServletConfig object for retrieval by getServletConfig(). When using either GenericServlet or HttpServlet, the default init() implementation handles this task. This method can also be used to perform any one-time actions required by the servlet, such as creating database connections. It is guaranteed to finish before any client requests are accepted.

service()

public abstract void service(ServletRequest req, ServletResponse res)
  throws ServletException, IOException
Description
Called to handle a single client request. A servlet receives request information via the ServletRequest object and sends data back to the client via the ServletResponse object.
ServletConfig

Synopsis

Interface Name: javax.servlet.ServletConfig
Superinterface: None
Immediate Subinterfaces: None
Implemented By: javax.servlet.GenericServlet
Availability: Servlet API 1.0 and later

Description

Servers use ServletConfig objects to pass initialization and context information to servlets. The initialization information generally consists of a series of initialization parameters (init parameters) and a ServletContext object, which provides information about the server environment. A servlet can implement Servlet-Config to allow easy access to init parameters and context information, as GenericServlet does.

Interface Declaration

public interface ServletConfig {  
  // Methods
  public abstract String getInitParameter(String name);
  public abstract Enumeration getInitParameterNames();
  public abstract ServletContext getServletContext();
}

Methods

getInitParameter()

public abstract String getInitParameter(String name)
Description
Returns the value of the named servlet initialization parameter or null if no matching parameter is found.

getInitParameterNames()

public abstract Enumeration getInitParameterNames()
Description
Returns the names of all the servlet's initialization parameters as an Enumeration of String objects or an empty Enumeration if no parameters exist.

getServletContext()

public abstract ServletContext getServletContext()
Description
Returns the ServletContext object for this servlet, allowing interaction with the server.
ServletContext

Synopsis

Interface Name: javax.servlet.ServletContext
Superinterface: None
Immediate Subinterfaces: None
Implemented By: None
Availability: Servlet API 1.0 and later

Description

The ServletContext interface defines a set of methods that can be used to communicate with the server in a non-request-specific manner. This includes finding path information, accessing other servlets running on the server, and writing to the server log file. Different virtual servers may return different servlet contexts.

Interface Declaration

public interface ServletContext {  
  // Methods
  public abstract Object getAttribute(String name);
  public abstract String getMimeType(String file);
  public abstract String getRealPath(String path);
  public abstract String getServerInfo();
  public abstract Servlet getServlet(String name) throws ServletException;
  public abstract Enumeration getServletNames();             // New in 2.0
  public abstract Enumeration getServlets();                 // Deprecated
  public abstract void log(Exception exception, String msg); // New in 2.0
  public abstract void log(String msg);
}

Methods

getAttribute()

public abstract Object getAttribute(String name)
Description
Returns the value of the named server attribute as an Object or null if the attribute does not exist. The attributes are server-dependent and allow web servers to provide servlets with information above and beyond that provided for by the base Servlet API. Attribute names should follow the same convention as package names. The package names java.* and javax.* are reserved for use by the Java Software division of Sun Microsystems (formerly known as JavaSoft), and com.sun.* is reserved for use by Sun Microsystems. See your server's documentation for a list of its attributes. Remember that servlets relying on server-specific attributes are not portable.

getMimeType()

public abstract String getMimeType(String file)
Description
Returns the MIME type of the given file or null if it is not known. Some implementations return "text/plain" if the specified file does not exist. Common MIME types are "text/html", "text/plain", "image/gif", and "image/jpeg".

getRealPath()

public abstract String getRealPath(String path)
Description
Returns the real file system path of any given "virtual path" or null if the translation cannot be performed. If the given path is "/", the method returns the document root for the servlet. If the given path is the same as the one returned by getPathInfo(), the method returns the same real path as would be returned by getPathTranslated(). There is no CGI counterpart.

getServerInfo()

public abstract String getServerInfo()
Description
Returns the name and version of the server software, separated by a forward slash (/). The value is the same as the CGI variable SERVER_SOFTWARE.

getServlet()

public abstract Servlet getServlet(String name) throws ServletException
Description
Returns the loaded servlet matching the given name or null if the servlet is not found. The specified name can be the servlet's registered name (e.g., "file") or class name (e.g., "com.sun.server.webserver .FileServlet"). The server maintains one servlet instance per name, so getServlet("file") returns a different servlet instance than get-Servlet("com.sun.server.webserver.FileServlet"). If the servlet implements SingleThreadModel, the server may return any instance of the servlet from the current pool. The server may--but is not required to--load the named servlet and execute its init() method if it was not already loaded. A ServletException is thrown if there is a problem during the load.

getServletNames()

public abstract Enumeration getServletNames()
Description
Returns an Enumeration of the names of the servlet objects loaded in this context. When used with getServlet(String name), it can replace the deprecated getServlets(). This method was introduced in the Servlet API 2.0.

getServlets()

public abstract Enumeration getServlets() throws ServletException
Description
Returns an Enumeration of the Servlet objects loaded in this context. This method was deprecated in the Servlet API 2.0 in favor of getServletNames().

log()

public abstract void log(Exception exception, String msg)
Description
Writes an exception's stack trace and a given message to a servlet log, usually an event log file. Both output format and location are server-specific. Notice the non-standard placement of the optional Exception parameter as the first parameter instead of the last. This method was introduced in the Servlet API 2.0.
public abstract void log(String msg)
Description
Writes the given message to a servlet log, usually an event log file. Both the output format and location are server-specific.
ServletException

Synopsis

Class Name: javax.servlet.ServletException
Superclass: java.lang.Exception
Immediate Subclasses:javax.servlet.UnavailableException
Interfaces Implemented: None
Availability: Servlet API 1.0 and later

Description

A generic exception thrown by servlets encountering difficulties.

Class Summary

public class ServletException extends java.lang.Exception {
  // Constructors
  public ServletException();                           // New in 2.0
  public ServletException(String msg);
}

Constructors

ServletException()

public ServletException()
public ServletException(String msg)
Description
Constructs a new ServletException , with an optional descriptive message. If a message is specified, it can be retrieved by calling getMessage() and is usually included in server logs and user error messages.
ServletInputStream

Synopsis

Class Name: javax.servlet.ServletInputStream
Superclass: java.io.InputStream
Immediate Subclasses: None
Interfaces Implemented: None
Availability: Servlet API 1.0 and later

Description

Provides an input stream for reading binary data from a client request, including an efficient readLine() method for reading data one line at a time. A ServletInputStream is returned by the getInputStream() method of ServletRequest. A servlet that filters binary output from other sources generally gets its input via this stream.

Class Summary

public abstract class ServletInputStream extends java.io.InputStream {
  // Constructors
  protected ServletInputStream();

  // Instance Methods
  public int readLine(byte b[], int off, int len) throws IOException;
}

Constructors

ServletInputStream()

protected ServletInputStream()
Description
The default constructor does nothing. Because servlets rarely, if ever, create their own input streams, it can be safely ignored.

Instance Methods

readLine()

public int readLine(byte b[], int off, int len) throws IOException
Description
Reads bytes from the input stream into the byte array b, starting at an offset in the array given by off. It stops reading when it encounters an '\n' or it has read len number of bytes. The ending '\n' character is read into the buffer as well. Returns the number of bytes read, or -1 if the end of the stream is reached.
ServletOutputStream

Synopsis

Class Name: javax.servlet.ServletOutputStream
Superclass: java.io.OutputStream
Immediate Subclasses: None
Interfaces Implemented: None
Availability: Servlet API 1.0 and later

Description

Provides an output stream for sending binary data back to a client. A servlet obtains a ServletOutputStream object from the getOutputStream() method of ServletResponse. Although it includes a range of print() and println() methods for sending text or HTML, the ServletOutputStream has been superseded by PrintWriter. It should be used only for sending binary data or with early servlet implementations built on the Servlet API 1.0.

If you subclass ServletOutputStream, you must provide an implementation of the write(int) method.

Class Summary

public abstract class ServletOutputStream extends java.io.OutputStream {
  // Constructors
  protected ServletOutputStream();

  // Instance Methods
  public void print(boolean b) throws IOException;
  public void print(char c) throws IOException;
  public void print(double d) throws IOException;
  public void print(float f) throws IOException;
  public void print(int i) throws IOException;
  public void print(long l) throws IOException;
  public void print(String s) throws IOException;
  public void println() throws IOException;
  public void println(boolean b) throws IOException;
  public void println(char c) throws IOException;
  public void println(double d) throws IOException;
  public void println(float f) throws IOException;
  public void println(int i) throws IOException;
  public void println(long l) throws IOException;
  public void println(String s) throws IOException;
}

Constructors

ServletOutputStream()

protected ServletOutputStream()
Description
The default constructor does nothing.

Instance Methods

print()

public void print(boolean b) throws IOException
public void print(char c) throws IOException
public void print(double d) throws IOException
public void print(float f) throws IOException
public void print(int i) throws IOException
public void print(long l) throws IOException
public void print(String s) throws IOException
Description
Writes the given data to the client, without a trailing carriage return/line feed (CRLF).

println()

public void println() throws IOException
public void println(boolean b) throws IOException
public void println(char c) throws IOException
public void println(double d) throws IOException
public void println(float f) throws IOException
public void println(int i) throws IOException
public void println(long l) throws IOException
public void println(String s) throws IOException
Description
Writes the given data to the client, with a trailing CRLF. The method with no parameters simply writes a CRLF.
ServletRequest

Synopsis

Interface Name: javax.servlet.ServletRequest
Superinterface: None
Immediate Subinterfaces: javax.servlet.http.HttpServletRequest
Implemented By: None
Availability: Servlet API 1.0 and later

Description

A ServletRequest object encapsulates information about a single client request, including request parameters, implementation-specific attributes, and an input stream for reading binary data from the request body. ServletRequest can be subclassed to provide additional protocol-specific information. HttpServletRequest, for instance, includes methods to manipulate HTTP headers.

Interface Declaration

public interface ServletRequest {
  // Methods
  public abstract Object getAttribute(String name);
  public abstract String getCharacterEncoding();                // New in 2.0
  public abstract int getContentLength();
  public abstract String getContentType();
  public abstract ServletInputStream getInputStream() throws IOException;
  public abstract String getParameter(String name);
  public abstract Enumeration getParameterNames();
  public abstract String[] getParameterValues(String name);
  public abstract String getProtocol();
  public abstract BufferedReader getReader() throws IOException;// New in 2.0
  public abstract String getRealPath(String path);
  public abstract String getRemoteAddr();
  public abstract String getRemoteHost();
  public abstract String getScheme();
  public abstract String getServerName();
  public abstract int getServerPort();
}

Methods

getAttribute()
public abstract Object getAttribute(String name)
Description
Returns the value of the named server-specific attribute as an Object, or null if the server does not support the named request attribute. Servers may use this method to provide servlets with custom information about a request. Attributes should follow the same conventions as package names, with the package names java.* and javax.* reserved for use by the Java Software division of Sun Microsystems (formerly known as JavaSoft), and com.sun.* reserved for use by Sun Microsystems. Remember that servlets that rely on server-specific request attributes are non-portable.

getCharacterEncoding()

public abstract String getCharacterEncoding()
Description
Returns the charset encoding for the servlet's input stream, or null if not known. This method was introduced in the Servlet API 2.0. It does not exist in the Java Web Server 1.1.x.

getContentLength()

public abstract int getContentLength()
Description
Returns the length, in bytes, of the content being sent via the input stream, or -1 if the length is not known (such as when there is no data). Equivalent to the CGI variable CONTENT_LENGTH.

getContentType()

public abstract String getContentType()
Description
Returns the media type of the content being sent via the input stream or null if the type is not known or there is no data. The same as the CGI variable CONTENT_TYPE.

getInputStream()

public abstract ServletInputStream getInputStream() throws IOException
Description
Retrieves the input stream as a ServletInputStream object. Servlet-InputStream is a direct subclass of InputStream and can be treated identically to a normal InputStream, with the added ability to efficiently read input a line at a time into an array of bytes. This method should be used for reading binary input. It throws an IllegalStateException if getReader() has been called before on the request. The IllegalState-Exception does not need to be explicitly caught.

getParameter()

public abstract String getParameter(String name)
Description
Returns the value of the named parameter as a String. Returns null if the parameter does not exist, or an empty string if the parameter exists but without a value. The value is guaranteed to be in its normal, decoded form. If the parameter has multiple values, the value returned is server dependent. If there is any chance that a parameter has more than one value, you should use the getParameterValues() method instead. If the parameter information came in as encoded POST data, it may not be available if the POST data has already been manually read using the getReader() or getInputStream() methods. This method was deprecated momentarily in favor of getParameterValues(), but thanks to an overwhelming flood of support from the developer community, it has been restored in the Servlet API 2.0.

getParameterNames()

public abstract Enumeration getParameterNames()
Description
Returns all the parameter names as an Enumeration of String objects. It returns an empty Enumeration if the servlet has no parameters.

getParameterValues()

public abstract String[] getParameterValues(String name)
Description
Returns all the values of the named parameter as an array of String objects, or null if the parameter does not exist. A single value is returned in an array of length 1.

getProtocol()

public abstract String getProtocol()
Description
Returns the name and version of the protocol used by the request as a string of the form protocol/major-version.minor-version. Equivalent to the CGI variable SERVER_PROTOCOL.

getReader()

public abstract BufferedReader getReader() throws IOException
Description
This method retrieves the input stream as a BufferedReader object, which should be used for reading character-based input, since the reader translates charsets as appropriate. This method throws an IllegalStateException if getInputStream() has been called before on this same request. It throws an UnsupportedEncodingException if the character encoding of the input is unsupported or unknown. This method was introduced in the Servlet API 2.0.

getRealPath()

public abstract String getRealPath(String path)
Description
Returns the real file system path of any given "virtual path" or null if the translation cannot be performed. If the given path is "/" it returns the document root for the server. If the given path is the same as the one returned by getPathInfo(), it returns the same real path as would be returned by getPathTranslated(). There is no CGI counterpart.

getRemoteAddr()

public abstract String getRemoteAddr()
Description
Returns the IP address of the client machine as a String. This information comes from the socket connecting the server to the client, so the remote address may be that of a proxy server. It is the same as the CGI variable REMOTE_ADDR.

getRemoteHost()

public abstract String getRemoteHost()
Description
Returns the name of the client host. This comes from the socket connecting the server to the client and may be the name of a proxy server. It is the same as the CGI variable REMOTE_HOST.

getScheme()

public abstract String getScheme()
Description
This method returns the scheme used to make this request. Examples include "http", "https", and "ftp", as well as the newer Java-specific schemes "jdbc" and "rmi".

getServerName()

public abstract String getServerName()
Description
Returns the name of the server that received the request. It is an attribute of the ServletRequest because it can change for different requests if the server has more than one name (a situation that might arise if one server is hosting more than one web site). Equivalent to the CGI variable SERVER_NAME.

getServerPort()

public abstract int getServerPort()
Description
Returns the port number on which this request was received. The same as the CGI variable SERVER_PORT.
ServletResponse

Synopsis

Interface Name: javax.servlet.ServletResponse
Superinterface: None
Immediate Subinterfaces: javax.servlet.http.HttpServletResponse
Interfaces Implemented: None
Availability: Servlet API 1.0 and later

Description

Servlets use ServletResponse objects to send MIME encoded data back to the client. The servlet engine creates this object and passes it to the servlet's service() method. To send binary data, use the ServletOutputStream returned by getOutputStream(). To send character data, use the PrintWriter returned by getWriter(). You can explicitly set the output's MIME type using the setContentType() method. If you elect to set this manually, do so before calling getWriter(), as getWriter() consults the content type to determine which charset to use. Consult RFC 2045 at http:/www.ietf.org/rfc/rfc2045.txt for more information on MIME.

Interface Declaration

public interface ServletResponse {
  // Methods
  public abstract String getCharacterEncoding();               // New in 2.0
  public abstract ServletOutputStream getOutputStream() throws IOException;
  public abstract PrintWriter getWriter() throws IOException;  // New in 2.0
  public abstract void setContentLength(int len);
  public abstract void setContentType(String type);
}

Methods

getCharacterEncoding()

public abstract String getCharacterEncoding()
Description
Returns the charset encoding used for this MIME body. This is the charset specified by the assigned content type or "ISO-8859-1" if no charset has been specified. This method was introduced in the Servlet API 2.0.

getOutputStream()

public abstract ServletOutputStream getOutputStream() throws IOException
Description
Returns a ServletOutputStream for writing binary (byte-at-a-time) response data. No encoding is performed. Throws an IllegalStateException if getWriter() has already been called on this response.

getWriter()

public abstract PrintWriter getWriter() throws IOException
Description
Returns a PrintWriter for writing character-based response data. The writer encodes the characters according to whatever charset is given in the content type. If no charset is specified in the content type, as is generally the case, the writer uses the ISO-8859-1 (Latin-1) encoding appropriate for Western European languages. Throws an IllegalStateException if getOutputStream() has already been called on this response, and an UnsupportedEncodingException if the encoding of the output stream is unsupported or unknown. This method was introduced in the Servlet API 2.0.

setContentLength()

public abstract void setContentLength(int len)
Description
Sets the length of the content being returned by the server. In HTTP servlets, it sets the HTTP Content-Length header. HTTP servlets use this method to enable persistent connections and help client progress monitors, so its use is optional.

setContentType()

public abstract void setContentType(String type)
Description
This method sets the content type of the response to be the specified type. In HTTP servlets, it sets the Content-Type HTTP header.
SingleThreadModel

Synopsis

Interface Name: javax.servlet.SingleThreadModel
Superinterface: None
Immediate Subinterfaces: None
Implemented By: None
Availability: New as of Servlet API 2.0; found in JSDK 2.0, JWS 1.1

Description

SingleThreadModel is a tag interface with no methods. If a servlet implements this interface, the server ensures that each instance of the servlet handles only one service request at a time. Servers implement this functionality by maintaining a pool of servlet instances and dispatching incoming requests to free servlets within the pool. SingleThreadModel provides easy thread safety, but at the cost of increased resource requirements as more servlet instances are loaded at any given time.

public interface SingleThreadModel { 
}
UnavailableException

Synopsis

Class Name: javax.servlet.UnavailableException
Superclass: javax.servlet.ServletException
Immediate Subclasses: None
Interfaces Implemented: None
Availability: Servlet API 1.0 and later

Description

A servlet can throw an UnavailableException at any time to indicate that it is not available to service client requests. There are two types of unavailability: permanent (where some corrective action must be taken on the server) and temporary. A servlet is temporarily unavailable if some system-wide problem momentarily prevents it from servicing requests. This may include network troubles or a crashed or overloaded database server. To mark a servlet as temporarily unavailable, specify a duration (in seconds) when constructing the exception. Well-written servers check back after this time. Servlet implementations are not required to treat temporary and permanent unavailability differently.

Servers generally provide clients with polite error messages when handling requests for unavailable servlets. For example, the Java Web Server returns a 404 (Unavailable) message.

Class Summary

public class UnavailableException extends ServletException {
  // Constructors
  public UnavailableException(int seconds, Servlet servlet, String msg);
  public UnavailableException(Servlet servlet, String msg);

  // Instance Methods
  public Servlet getServlet();
  public int getUnavailableSeconds();
  public boolean isPermanent();
}

Constructors

UnavailableException()

public UnavailableException(int seconds, Servlet servlet, String msg)
public UnavailableException(Servlet servlet, String msg)
Description
Constructs an UnavailableException with a given explanatory message. You can optionally specify a period of unavailability, given in seconds. If no time estimate can be made, a nonpositive value can be passed to the constructor, indicating permanent unavailability. Notice the nonstandard placement of the optional seconds parameter as the first parameter instead of the last. This may be changed in an upcoming release.

getServlet()

public Servlet getServlet()
Description
Returns the servlet that threw this exception.

getUnavailableSeconds()

public int getUnavailableSeconds()
Description
Returns the number of seconds for which this servlet will be unavailable. A negative number indicates permanent unavailability. No attempt is made to compensate for the time elapsed since the exception was thrown.

isPermanent()

public boolean isPermanent()
Description
Returns true if the servlet is unavailable indefinitely, false otherwise.


Library Navigation Links

Copyright © 2001 O'Reilly & Associates. All rights reserved.







??????????????@Mail.ru