## The Manager Component

### Table of Contents

- Introduction
- Attributes
  1. Common Attributes
  2. Standard Implementation
- Nested Components
- Special Features
  1. Persistence Across Restarts
  2. Enable Session Persistence

### Introduction

The Manager element represents the session manager that will be used to create and maintain HTTP sessions as requested by the associated web application.

A Manager element MAY be nested inside a Context component. If it is not included, a default Manager configuration will be created automatically, which is sufficient for most requirements, — see Standard Manager Implementation below for the details of this configuration.

### Attributes

#### Common Attributes

All implementations of Manager support the following attributes:

Attribute | Description
--- | ---
`className` | Java class name of the implementation to use. This class must implement the `org.apache.catalina.Manager` interface. If not specified, the standard value (defined below) will be used.
`maxActiveSessions` | The maximum number of active sessions that will be created by this Manager, or `-1` (the default) for no limit. When the limit is reached, any attempt to create a new session (e.g. with `HttpServletRequest.getSession()` call) will fail with an `IllegalStateException`.
`notifyAttributeListenerOnUnchangedValue` | If an attribute is added to the session and that attribute is already present in the session under the same name will any `HttpSessionAttributeListener` be notified that the attribute has been replaced. If not specified, the default value of `true` will be used.
`notifyBindingListenerOnUnchangedValue` | If an attribute is added to the session, that attribute is already present in the session under the same name and the attribute implements `HttpSessionBindingListener`, will the listener be notified that the attribute has been unbound and bound again. If not specified, the default value of `false` will be used.
`sessionActivityCheck` | If this is `true`, Tomcat will track the number of active requests for each session. When determining if a session is valid, any session with at least one active request will always be considered valid. If `org.apache.catalina.STRICT_SERVLET_COMPLIANCE` is set to `true`, the default of this setting will be `true`, else the default value will be `false`.
`sessionLastAccessAtStart` | If this is `true`, the last accessed time for sessions will be calculated from the beginning of the previous request. If `false`, the last accessed time for sessions will be calculated from the end of the previous request. This also affects how the idle time is calculated. If `org.apache.catalina.STRICT_SERVLET_COMPLIANCE` is set to `true`, the default of this setting will be `true`, else the default value will be `false`.

#### Standard Implementation

Tomcat provides two standard implementations of Manager for use — the default one stores active sessions, while the optional one stores active sessions that have been swapped out (in addition to saving sessions across a restart of Tomcat) in a storage location that is selected via the use of an appropriate Store nested element.

### Standard Manager Implementation

The standard implementation of Manager is org.apache.catalina.session.StandardManager. It supports the following additional attributes (in addition to the common attributes listed above):

Attribute | Description
--- | ---
`pathname` | Absolute or relative (to the work directory for this Context) pathname of the file in which session state will be preserved across application restarts, if possible. The default is null. See Persistence Across Restarts for more information. This persistence may be enabled by setting this attribute to a non empty string.
`persistAuthentication` | Should authentication information be included when session state is preserved across application restarts? If `true`, the session's authentication is preserved so that the session remains authenticated after the application has been restarted. If not specified, the default value of `false` will be used. See Persistence Across Restarts for more information. Please note that the session's `Principal` class as well as its descendant classes are all subject to the sessionAttributeValueClassNameFilter. If such a filter is specified or a `SecurityManager` is enabled, the names of the `Principal` class and descendant classes must match that filter pattern in order to be restored.
`processExpiresFrequency` | Frequency of the session expiration, and related manager operations. Manager operations will be done once for the specified amount of backgroundProcess calls (i.e., the lower the amount, the more often the checks will occur). The minimum value is 1, and the default value is 6.
`secureRandomClass` | Name of the Java class that extends `java.security.SecureRandom` to use to generate session IDs. If not specified, the default value is `java.security.SecureRandom`.
`secureRandomProvider` | Name of the provider to use to create the `java.security.SecureRandom` instances that generate session IDs. If an invalid algorithm and/or provider is specified, the Manager will use the platform default provider and the default algorithm. If not specified, the platform default provider will be used.
`secureRandomAlgorithm` | Name of the algorithm to use to create the `java.security.SecureRandom` instances that generate session IDs. If an invalid algorithm and/or provider is specified, the Manager will use the platform default provider and the default algorithm. If not specified, the default algorithm of SHA1PRNG will be used. If the default algorithm is not supported, the platform default will be used. To specify that the platform default should be used, do not set the secureRandomProvider attribute and set this attribute to the empty string.
`sessionAttributeNameFilter` | A regular expression used to filter which session attributes will be distributed. An attribute will only be distributed if its name matches this pattern. If the pattern is zero length or `null`, all attributes are eligible for distribution. The pattern is anchored so the session attribute name must fully match the pattern. As an example, the value `(userName|sessionHistory)` will only distribute the two session attributes named `userName` and `sessionHistory`. If not specified, the default value of `null` will be used.
`sessionAttributeValueClassNameFilter` | A regular expression used to filter which session attributes will be distributed. An attribute will only be distributed if the implementation class name of the value matches this pattern. If the pattern is zero length or `null`, all attributes are eligible for distribution. The pattern is anchored so the fully qualified class name must fully match the pattern. If not specified, the default value of `null` will be used unless a `SecurityManager` is enabled in which case the default will be `java\\.lang\\.(?:Boolean|Integer|Long|Number|String)|org\\.apache\\.catalina\\.realm\\.GenericPrincipal\\$SerializablePrincipal|\\[Ljava.lang.String;`.
`warnOnSessionAttributeFilterFailure` | If sessionAttributeNameFilter or sessionAttributeValueClassNameFilter blocks an attribute, should this be logged at `WARN` level? If `WARN` level logging is disabled then it will be logged at `DEBUG`. The default value of this attribute is `false` unless a `SecurityManager` is enabled in which case the default will be `true`.

### Persistent Manager Implementation

NOTE: You must set either the `org.apache.catalina.session.StandardSession.ACTIVITY_CHECK` or `org.apache.catalina.STRICT_SERVLET_COMPLIANCE` system properties to `true` for the persistent manager to work correctly.

The persistent implementation of Manager is org.apache.catalina.session.PersistentManager. In addition to the usual operations of creating and deleting sessions, a `PersistentManager` has the capability to swap active (but idle) sessions out to a persistent storage mechanism, as well as to save all sessions across a normal restart of Tomcat. The actual persistent storage mechanism used is selected by your choice of a Store element nested inside the Manager element - this is required for use of `PersistentManager`.

This implementation of Manager supports the following attributes in addition to the Common Attributes described earlier.

Attribute | Description
--- | ---
`className` | It has the same meaning as described in the Common Attributes above. You must specify `org.apache.catalina.session.PersistentManager` to use this manager implementation.
`maxIdleBackup` | The time interval (in seconds) since the last access to a session before it is eligible for being persisted to the session store, or `-1` to disable this feature. By default, this feature is disabled.
`maxIdleSwap` | The maximum time a session may be idle before it is eligible to be swapped to disk due to inactivity. Setting this to `-1` means sessions should not be swapped out just because of inactivity. If this feature is enabled, the time interval specified here should be equal to or longer than the value specified for `maxIdleBackup`. By default, this feature is disabled.
`minIdleSwap` | The minimum time in seconds a session must be idle before it is eligible to be swapped to disk to keep the active session count below maxActiveSessions. Setting to `-1` means sessions will not be swapped out to keep the active session count down. If specified, this value should be less than that specified by `maxIdleSwap`. By default, this value is set to `-1`.
`persistAuthentication` | Should authentication information be included when sessions are swapped out to persistent storage? If `true`, the session's authentication is preserved so that the session remains authenticated after being reloaded (swapped in) from persistent storage. If not specified, the default value of `false` will be used. Please note that the session's `Principal` class as well as its descendant classes are all subject to the sessionAttributeValueClassNameFilter. If such a filter is specified or a `SecurityManager` is enabled, the names of the `Principal` class and descendant classes must match that filter pattern in order to be restored.
`processExpiresFrequency` | It is the same as described above for the `org.apache.catalina.session.StandardManager` class.
`saveOnRestart` | Should all sessions be persisted and reloaded when Tomcat is shut down and restarted (or when this application is reloaded)? By default, this attribute is set to `true`.
`secureRandomClass` | It is the same as described above for the `org.apache.catalina.session.StandardManager` class.
`secureRandomProvider` | It is the same as described above for the `org.apache.catalina.session.StandardManager` class.
`secureRandomAlgorithm` | It is the same as described above for the `org.apache.catalina.session.StandardManager` class.
`sessionAttributeNameFilter` | A regular expression used to filter which session attributes will be distributed. An attribute will only be distributed if its name matches this pattern. If the pattern is zero length or `null`, all attributes are eligible for distribution. The pattern is anchored so the session attribute name must fully match the pattern. As an example, the value `(userName|sessionHistory)` will only distribute the two session attributes named `userName` and `sessionHistory`. If not specified, the default value of `null` will be used.
`sessionAttributeValueClassNameFilter` | A regular expression used to filter which session attributes will be distributed. An attribute will only be distributed if the implementation class name of the value matches this pattern. If the pattern is zero length or `null`, all attributes are eligible for distribution. The pattern is anchored so the fully qualified class name must fully match the pattern. If not specified, the default value of `null` will be used unless a `SecurityManager` is enabled in which case the default will be `java\\.lang\\.(?:Boolean|Integer|Long|Number|String)|org\\.apache\\.catalina\\.realm\\.GenericPrincipal\\$SerializablePrincipal|\\[Ljava.lang.String;`.
`warnOnSessionAttributeFilterFailure` | If sessionAttributeNameFilter or sessionAttributeValueClassNameFilter blocks an attribute, should this be logged at `WARN` level? If `WARN` level logging is disabled then it will be logged at `DEBUG`. The default value of this attribute is `false` unless a `SecurityManager` is enabled in which case the default will be `true`.

In order to successfully use a PersistentManager, you must nest inside it a <Store> element, as described below.

### Nested Components

### All Manager Implementations

All Manager implementations allow nesting of a <SessionIdGenerator> element. It defines the behavior of session id generation. All implementations of the SessionIdGenerator allow the following attributes:

Attribute | Description
--- | ---
`sessionIdLength` | The length of the session ID may be changed with the sessionIdLength attribute.

### Persistent Manager Implementation

If you are using the Persistent Manager Implementation as described above, you MUST nest a <Store> element inside, which defines the characteristics of the persistent data storage. Two implementations of the `<Store>` element are currently available, with different characteristics, as described below.

##### File Based Store

The File Based Store implementation saves swapped out sessions in individual files (named based on the session identifier) in a configurable directory. Therefore, you are likely to encounter scalability problems as the number of active sessions increases, and this should primarily be considered a means to easily experiment.

To configure this, add a `<Store>` nested inside your `<Manager>` element with the following attributes:

Attribute | Description
--- | ---
`className` | Java class name of the implementation to use. This class must implement the `org.apache.catalina.Store` interface. You must specify `org.apache.catalina.session.FileStore` to use this implementation.
`directory` | Absolute or relative (to the temporary work directory for this web application) pathname of the directory into which individual session files are written. If not specified, the temporary work directory assigned by the container is utilized.

##### Data source Based Store

The Data source Based Store implementation saves swapped out sessions in individual rows of a preconfigured table in a database that is accessed via a data sourcer. With large numbers of swapped out sessions, this implementation will exhibit improved performance over the File Based Store described above.

To configure this, add a `<Store>` nested inside your `<Manager>` element with the following attributes:

Attribute | Description
--- | ---
`className` | Java class name of the implementation to use. This class must implement the `org.apache.catalina.Store` interface. You must specify `org.apache.catalina.session.DataSourceStore` to use this implementation.
`dataSourceName` | Name of the JNDI resource for a JDBC DataSource-factory. Since this code uses prepared statements, you might want to configure pooled prepared statements as shown in the JNDI resources How-To.
`localDataSource` | This allows the Store to use a DataSource defined for the Context rather than a global DataSource. If not specified, the default is `false`: use a global DataSource.
`sessionAppCol` | Name of the database column, contained in the specified session table, that contains the Engine, Host, and Web Application Context name in the format `/Engine/Host/Context`. If not specified the default value of `app` will be used.
`sessionDataCol` | Name of the database column, contained in the specified session table, that contains the serialized form of all session attributes for a swapped out session. The column type must accept a binary object (typically called a BLOB). If not specified the default value of `data` will be used.
`sessionIdCol` | Name of the database column, contained in the specified session table, that contains the session identifier of the swapped out session. The column type must accept character string data of at least as many characters as are contained in session identifiers created by Tomcat (typically 32). If not specified the default value of `id` will be used.
`sessionLastAccessedCol` | Name of the database column, contained in the specified session table, that contains the `lastAccessedTime` property of this session. The column type must accept a Java `long` (64 bits). If not specified the default value of `maxinactive` will be used.
`sessionMaxInactiveCol` | Name of the database column, contained in the specified session table, that contains the `maxInactiveInterval` property of this session. The column type must accept a Java `integer` (32 bits). If not specified, the default value of `maxinactive` will be used.
`sessionTable` | Name of the database table to be used for storing swapped out sessions. This table must contain (at least) the database columns that are configured by the other attributes of this element. If not specified the default value of `tomcat$sessions` will be used.
`sessionValidCol` | Name of the database column, contained in the specified session table, that contains a flag indicating whether this swapped out session is still valid or not. The column type must accept a single character. If not specified the default value of `valid` will be used.

Before attempting to use the data source Store for the first time, you must create the table that will be used to store swapped out sessions. Detailed SQL commands vary depending on the database you are using, but a script like this will generally be required:

    create table tomcat_sessions (
      session_id     varchar(100) not null primary key,
      valid_session  char(1) not null,
      max_inactive   int not null,
      last_access    bigint not null,
      app_name       varchar(255),
      session_data   mediumblob,
      KEY kapp_name(app_name)
    );

Note: The SQL command above does not use the default names for either the table or the columns so the data source Store would need to be configured to reflect this.

### Special Features

#### Persistence Across Restarts

Whenever Apache Tomcat is shut down normally and restarted, or when an application reload is triggered, the standard Manager implementation will attempt to serialize all currently active sessions to a disk file located via the `pathname` attribute. All such saved sessions will then be deserialized and activated (assuming they have not expired in the mean time) when the application reload is completed.

In order to successfully restore the state of session attributes, all such attributes MUST implement the `java.io.Serializable` interface. You MAY cause the Manager to enforce this restriction by including the `<distributable>` element in your web application deployment descriptor (`/WEB-INF/web.xml`).

Note that, if persistAuthentication is also set to `true`, the `Principal` class present in the session MUST also implement the `java.io.Serializable` interface in order to make authentication persistence work properly. The actual type of that `Principal` class is determined by the Realm implementation used with the application. Tomcat's standard `Principal` class instantiated by most of the Realms (except `JAASRealm`) implements `java.io.Serializable`.

The persistence across restarts provided by the StandardManager is a simpler implementation than that provided by the PersistentManager. If robust, production quality persistence across restarts is required then the PersistentManager should be used with an appropriate configuration.

#### Enable Session Persistence

As documented above, every web application by default has standard manager implementation configured, which can perform session persistence across restarts. To enable this persistence feature, create a Context configuration file for your web application and add the following element there (in this example, it will save sessions to files named `SESSIONS.ser`):

    <Manager pathname="SESSIONS.ser" />