Server (Apache Hadoop HttpFS 3.0.2 API)

java.lang.Object
- org.apache.hadoop.lib.server.Server

Direct Known Subclasses:

ServerWebApp
```
@InterfaceAudience.Private
public class Server
extends Object
```
A Server class provides standard configuration, logging and Service lifecyle management.
A Server normally has a home directory, a configuration directory, a temp directory and logs directory.
The Server configuration is loaded from 2 overlapped files, #SERVER#-default.xml and #SERVER#-site.xml. The default file is loaded from the classpath, the site file is laoded from the configuration directory.
The Server collects all configuration properties prefixed with #SERVER#. The property names are then trimmed from the #SERVER# prefix.
The Server log configuration is loaded from the #SERVICE#-log4j.properties file in the configuration directory.
The lifecycle of server is defined in by Server.Status enum. When a server is create, its status is UNDEF, when being initialized it is BOOTING, once initialization is complete by default transitions to NORMAL. The #SERVER#.startup.status configuration property can be used to specify a different startup status (NORMAL, ADMIN or HALTED).
Services classes are defined in the #SERVER#.services and #SERVER#.services.ext properties. They are loaded in order (services first, then services.ext).
Before initializing the services, they are traversed and duplicate service interface are removed from the service list. The last service using a given interface wins (this enables a simple override mechanism).
After the services have been resoloved by interface de-duplication they are initialized in order. Once all services are initialized they are post-initialized (this enables late/conditional service bindings).

Nested Class Summary

Nested Classes
Modifier and Type Class and Description

static class Server.Status
Enumeration that defines the server status.

Nested Classes
Modifier and Type	Class and Description
`static class`	`Server.Status` Enumeration that defines the server status.

Field Summary

Fields
Modifier and Type	Field and Description
`static String`	`CONF_SERVICES` Server property name that defines the service classes.
`static String`	`CONF_SERVICES_EXT` Server property name that defines the service extension classes.
`static String`	`CONF_STARTUP_STATUS` Server property name that defines server startup status.
`static String`	`DEFAULT_LOG4J_PROPERTIES` Name of the log4j configuration file the Server will load from the classpath if the `#SERVER#-log4j.properties` is not defined in the server configuration directory.

Constructor Summary

Constructors
Constructor and Description
`Server(String name, String homeDir)` Creates a server instance.
`Server(String name, String homeDir, org.apache.hadoop.conf.Configuration config)` Creates a server instance.
`Server(String name, String homeDir, String configDir, String logDir, String tempDir)` Creates a server instance.
`Server(String name, String homeDir, String configDir, String logDir, String tempDir, org.apache.hadoop.conf.Configuration config)` Creates a server instance.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`protected void`	`checkServiceDependencies(Service service)` Checks if all service dependencies of a service are available.
`void`	`destroy()` Destroys the server.
`protected void`	`destroyServices()` Destroys the server services.
`protected void`	`ensureOperational()` Verifies the server is operational.
`<T> T`	`get(Class<T> serviceKlass)` Returns the `Service` associated to the specified interface.
`org.apache.hadoop.conf.Configuration`	`getConfig()` Returns the server configuration.
`String`	`getConfigDir()` Returns the server config dir.
`String`	`getHomeDir()` Returns the server home dir.
`String`	`getLogDir()` Returns the server log dir.
`String`	`getName()` Returns the name of the server.
`String`	`getPrefix()` Returns the server prefix for server configuration properties.
`String`	`getPrefixedName(String name)` Returns the prefixed name of a server property.
`Server.Status`	`getStatus()` Returns the current server status.
`String`	`getTempDir()` Returns the server temp dir.
`void`	`init()` Initializes the Server.
`protected void`	`initConfig()` Loads and inializes the server configuration.
`protected void`	`initLog()` Initializes Log4j logging.
`protected void`	`initServices(List<Service> services)` Initializes the list of services.
`protected List<Service>`	`loadServices()` Loads services defined in `services` and `services.ext` and de-dups them.
`void`	`setService(Class<? extends Service> klass)` Adds a service programmatically.
`void`	`setStatus(Server.Status status)` Sets a new server status.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - CONF_SERVICES
```
public static final String CONF_SERVICES
```
    Server property name that defines the service classes.
    
    See Also:
    
    Constant Field Values
  - CONF_SERVICES_EXT
```
public static final String CONF_SERVICES_EXT
```
    Server property name that defines the service extension classes.
    
    See Also:
    
    Constant Field Values
  - CONF_STARTUP_STATUS
```
public static final String CONF_STARTUP_STATUS
```
    Server property name that defines server startup status.
    
    See Also:
    
    Constant Field Values
  - DEFAULT_LOG4J_PROPERTIES
```
public static final String DEFAULT_LOG4J_PROPERTIES
```
    Name of the log4j configuration file the Server will load from the classpath if the #SERVER#-log4j.properties is not defined in the server configuration directory.
    
    See Also:
    
    Constant Field Values
- Constructor Detail
  - Server
```
public Server(String name,
              String homeDir)
```
    Creates a server instance.
    The config, log and temp directories are all under the specified home directory.
    
    Parameters:
    
    name - server name.
    
    homeDir - server home directory.
  - Server
```
public Server(String name,
              String homeDir,
              String configDir,
              String logDir,
              String tempDir)
```
    Creates a server instance.
    
    Parameters:
    
    name - server name.
    
    homeDir - server home directory.
    
    configDir - config directory.
    
    logDir - log directory.
    
    tempDir - temp directory.
  - Server
```
public Server(String name,
              String homeDir,
              org.apache.hadoop.conf.Configuration config)
```
    Creates a server instance.
    The config, log and temp directories are all under the specified home directory.
    It uses the provided configuration instead loading it from the config dir.
    
    Parameters:
    
    name - server name.
    
    homeDir - server home directory.
    
    config - server configuration.
  - Server
```
public Server(String name,
              String homeDir,
              String configDir,
              String logDir,
              String tempDir,
              org.apache.hadoop.conf.Configuration config)
```
    Creates a server instance.
    It uses the provided configuration instead loading it from the config dir.
    
    Parameters:
    
    name - server name.
    
    homeDir - server home directory.
    
    configDir - config directory.
    
    logDir - log directory.
    
    tempDir - temp directory.
    
    config - server configuration.
- Method Detail
  - getStatus
```
public Server.Status getStatus()
```
    Returns the current server status.
    
    Returns:
    
    the current server status.
  - setStatus
```
public void setStatus(Server.Status status)
               throws ServerException
```
    Sets a new server status.
    The status must be settable.
    All services will be notified o the status change via the Service.serverStatusChange(Server.Status, Server.Status) method. If a service throws an exception during the notification, the server will be destroyed.
    
    Parameters:
    
    status - status to set.
    
    Throws:
    
    ServerException - thrown if the service has been destroy because of a failed notification to a service.
  - ensureOperational
```
protected void ensureOperational()
```
    Verifies the server is operational.
    
    Throws:
    
    IllegalStateException - thrown if the server is not operational.
  - init
```
public void init()
          throws ServerException
```
    Initializes the Server.
    The initialization steps are:
    - It verifies the service home and temp directories exist
    - Loads the Server #SERVER#-default.xml configuration file from the classpath
    - Initializes log4j logging. If the #SERVER#-log4j.properties file does not exist in the config directory it load default-log4j.properties from the classpath
    - Loads the #SERVER#-site.xml file from the server config directory and merges it with the default configuration.
    - Loads the services
    - Initializes the services
    - Post-initializes the services
    - Sets the server startup status
    Throws:
    
    ServerException - thrown if the server could not be initialized.
  - initLog
```
protected void initLog()
                throws ServerException
```
    Initializes Log4j logging.
    
    Throws:
    
    ServerException - thrown if Log4j could not be initialized.
  - initConfig
```
protected void initConfig()
                   throws ServerException
```
    Loads and inializes the server configuration.
    
    Throws:
    
    ServerException - thrown if the configuration could not be loaded/initialized.
  - loadServices
```
protected List<Service> loadServices()
                              throws ServerException
```
    Loads services defined in services and services.ext and de-dups them.
    
    Returns:
    
    List of final services to initialize.
    
    Throws:
    
    ServerException - throw if the services could not be loaded.
  - initServices
```
protected void initServices(List<Service> services)
                     throws ServerException
```
    Initializes the list of services.
    
    Parameters:
    
    services - services to initialized, it must be a de-dupped list of services.
    
    Throws:
    
    ServerException - thrown if the services could not be initialized.
  - checkServiceDependencies
```
protected void checkServiceDependencies(Service service)
                                 throws ServerException
```
    Checks if all service dependencies of a service are available.
    
    Parameters:
    
    service - service to check if all its dependencies are available.
    
    Throws:
    
    ServerException - thrown if a service dependency is missing.
  - destroyServices
```
protected void destroyServices()
```
    Destroys the server services.
  - destroy
```
public void destroy()
```
    Destroys the server.
    All services are destroyed in reverse order of initialization, then the Log4j framework is shutdown.
  - getName
```
public String getName()
```
    Returns the name of the server.
    
    Returns:
    
    the server name.
  - getPrefix
```
public String getPrefix()
```
    Returns the server prefix for server configuration properties.
    By default it is the server name.
    
    Returns:
    
    the prefix for server configuration properties.
  - getPrefixedName
```
public String getPrefixedName(String name)
```
    Returns the prefixed name of a server property.
    
    Parameters:
    
    name - of the property.
    
    Returns:
    
    prefixed name of the property.
  - getHomeDir
```
public String getHomeDir()
```
    Returns the server home dir.
    
    Returns:
    
    the server home dir.
  - getConfigDir
```
public String getConfigDir()
```
    Returns the server config dir.
    
    Returns:
    
    the server config dir.
  - getLogDir
```
public String getLogDir()
```
    Returns the server log dir.
    
    Returns:
    
    the server log dir.
  - getTempDir
```
public String getTempDir()
```
    Returns the server temp dir.
    
    Returns:
    
    the server temp dir.
  - getConfig
```
public org.apache.hadoop.conf.Configuration getConfig()
```
    Returns the server configuration.
    
    Returns:
    
    the server configuration.
  - get
```
public <T> T get(Class<T> serviceKlass)
```
    Returns the Service associated to the specified interface.
    
    Parameters:
    
    serviceKlass - service interface.
    
    Returns:
    
    the service implementation.
  - setService
```
public void setService(Class<? extends Service> klass)
                throws ServerException
```
    Adds a service programmatically.
    If a service with the same interface exists, it will be destroyed and removed before the given one is initialized and added.
    If an exception is thrown the server is destroyed.
    
    Parameters:
    
    klass - service class to add.
    
    Throws:
    
    ServerException - throw if the service could not initialized/added to the server.

Class Server

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

CONF_SERVICES

CONF_SERVICES_EXT

CONF_STARTUP_STATUS

DEFAULT_LOG4J_PROPERTIES

Constructor Detail

Server

Server

Server

Server

Method Detail

getStatus

setStatus

ensureOperational

init

initLog

initConfig

loadServices

initServices

checkServiceDependencies

destroyServices

destroy

getName

getPrefix

getPrefixedName

getHomeDir

getConfigDir

getLogDir

getTempDir

getConfig

get

setService