## The LifeCycle Listener Component

### Table of Contents

- Introduction
- Attributes
  1. Common Attributes
- Nested Components
- Standard Implementations
  1. APR Lifecycle Listener - org.apache.catalina.core.AprLifecycleListener
  2. Global Resources Lifecycle Listener - org.apache.catalina.mbeans.GlobalResourcesLifecycleListener
  3. JNI Library Loading Listener - org.apache.catalina.core.JniLifecycleListener
  4. JRE Memory Leak Prevention Listener - org.apache.catalina.core.JreMemoryLeakPreventionListener
     1. JreMemoryLeakPreventionListener Examples
  5. Security Lifecycle Listener - org.apache.catalina.security.SecurityListener
  6. StoreConfig Lifecycle Listener - org.apache.catalina.storeconfig.StoreConfigLifecycleListener
  7. ThreadLocal Leak Prevention Listener - org.apache.catalina.core.ThreadLocalLeakPreventionListener
  8. UserConfig - org.apache.catalina.startup.UserConfig
  9. Version Logging Lifecycle Listener - org.apache.catalina.startup.VersionLoggerListener
- Additional Implementations
  1. System property replacement - org.apache.catalina.util.SystemPropertyReplacerListener

### Introduction

A Listener element defines a component that performs actions when specific events occur, usually Tomcat starting or Tomcat stopping.

Listeners may be nested inside a Server, Engine, Host or Context. Some Listeners are only intended to be nested inside specific elements. These constraints are noted in the documentation below.

### Attributes

#### Common Attributes

All implementations of Listener support the following attributes:

Attribute | Description
--- | ---
`className` | Java class name of the implementation to use. This class must implement the `org.apache.catalina.LifecycleListener` interface.

### Nested Components

No element may be nested inside a Listener.

### Standard Implementations

Unlike most Catalina components, there are several standard Listener implementations available. As a result, the `className` attribute MUST be used to select the implementation you wish to use.

#### APR Lifecycle Listener - org.apache.catalina.core.AprLifecycleListener

The APR Lifecycle Listener checks for the presence of the APR/native library and loads the library if it is present. For more information see the APR/native guide.

This listener must only be nested within Server elements.

The following additional attributes are supported by the APR Lifecycle Listener:

Attribute | Description
--- | ---
`SSLEngine` | Name of the SSLEngine to use. `off`: do not use SSL, `on`: use SSL but no specific ENGINE. The default value is on. This initializes the native SSL engine, which must be enabled in the APR/native connector by the use of the `SSLEnabled` attribute. See the Official OpenSSL website for more details on supported SSL hardware engines and manufacturers. Tomcat Native 2.x onwards requires SSL so if SSLEngine is set to `off` when using Tomcat Native 2.x onwards, the APR/native library will be disabled.
`SSLRandomSeed` | Entropy source used to seed the SSLEngine's PRNG. The default value is `builtin`. On development systems, you may want to set this to `/dev/urandom` to allow quicker start times.
`FIPSMode` | The behaviour of this attribute depends on whether Tomcat Native has been compiled against OpenSSL 1.x or OpenSSL 3.x. For OpenSSL 1.x: Set to `on` to request that OpenSSL be in FIPS mode (if OpenSSL is already in FIPS mode, it will remain in FIPS mode). Set to `enter` to force OpenSSL to enter FIPS mode (an error will occur if OpenSSL is already in FIPS mode). Set to `require` to require that OpenSSL already be in FIPS mode (an error will occur if OpenSSL is not already in FIPS mode). For OpenSSL 3.x: `on`, `enter` and `require` all behave the same way. If the FIPS provider is the default provider, it will be used. If the FIPS provider is not the default provider, an error will occur. FIPS mode requires you to have a FIPS-capable OpenSSL library. If this attribute is set to anything other than `off`, the SSLEngine must be enabled as well. The default value is `off`.
`useAprConnector` | This attribute controls the auto-selection of the connector implementation. When the protocol is specified as `HTTP/1.1` or `AJP/1.3` then if this attribute is `true` the APR/native connector will be used but if this attribute is false the NIO connector will be used.
`useOpenSSL` | This attribute controls the auto-selection of the OpenSSL JSSE implementation. The default is `true` which will use OpenSSL if the native library is available and a NIO or NIO2 connector is used.

#### Global Resources Lifecycle Listener - org.apache.catalina.mbeans.GlobalResourcesLifecycleListener

The Global Resources Lifecycle Listener initializes the Global JNDI resources defined in server.xml as part of the Global Resources element. Without this listener, none of the Global Resources will be available.

This listener must only be nested within Server elements.

No additional attributes are supported by the Global Resources Lifecycle Listener.

#### JNI Library Loading Listener - org.apache.catalina.core.JniLifecycleListener

The JNI Library Loading Listener makes it possible for multiple Webapps to use a native library, by loading the native library using a shared class loader (typically the Common class loader but may vary in some configurations)

The listener supports two mutually exclusive attributes, so one of them must be used, but you can not use both together:

Attribute | Description
--- | ---
`libraryName` | The name of the native library, as defined in `java.lang.System.loadLibrary()`
`libraryPath` | The absolute path of the native library, as defined in `java.lang.System.load()`

#### JRE Memory Leak Prevention Listener - org.apache.catalina.core.JreMemoryLeakPreventionListener

The JRE Memory Leak Prevention Listener provides work-arounds for known places where the Java Runtime environment uses the context class loader to load a singleton as this will cause a memory leak if a web application class loader happens to be the context class loader at the time. The work-around is to initialise these singletons when this listener starts as Tomcat's common class loader is the context class loader at that time. It also provides work-arounds for known issues that can result in locked JAR files.

This listener must only be nested within Server elements.

The following additional attributes are supported by the JRE Memory Leak Prevention Listener:

Attribute | Description
--- | ---
`appContextProtection` | Enables protection so that calls to `sun.awt.AppContext.getAppContext()` triggered by a web application do not result in a memory leak. Note that enabling this protection will trigger a requirement for a graphical environment unless Java is started in head-less mode. The default is `false`. This protection is disabled if running on Java 8 onwards since the leak has been fixed for Java 8 onwards.
`AWTThreadProtection` | Enables protection so that calls to `java.awt.Toolkit.getDefaultToolkit()` triggered by a web application do not result in a memory leak. Defaults to `false` because an AWT thread is launched. This protection is disabled if running on Java 9 onwards since the leak has been fixed for Java 9 onwards.
`classesToInitialize` | List of comma-separated fully qualified class names to load and initialize during the startup of this Listener. This allows to pre-load classes that are known to provoke classloader leaks if they are loaded during a request processing. Non-JRE classes may be referenced, like `oracle.jdbc.driver.OracleTimeoutThreadPerVM`. The default value is empty, but specific JRE classes are loaded by other leak protection features managed by other attributes of this Listener.
`driverManagerProtection` | The first use of `java.sql.DriverManager` will trigger the loading of JDBC Drivers visible to the current class loader and its parents. The web application level memory leak protection can take care of this in most cases but triggering the loading here has fewer side-effects. The default is `true`.
`forkJoinCommonPoolProtection` | Enables protection so the threads created for `ForkJoinPool.commonPool()` do not result in a memory leak. The protection is enabled by setting the `java.util.concurrent.ForkJoinPool.common.threadFactory` system property. If this property is set when Tomcat starts, Tomcat will not over-ride it even if this protection is explicitly enabled. The default is `true`. This protection is only used when running on Java 8. The common pool does not exist in earlier versions and the leak has been fixed for Java 9 onwards.
`gcDaemonProtection` | Enables protection so that calls to `sun.misc.GC.requestLatency(long)` triggered by a web application do not result in a memory leak. Use of RMI is likely to trigger a call to this method. A side effect of enabling this protection is the creation of a thread named "GC Daemon". The protection uses reflection to access internal Sun classes and may generate errors on startup on non-Sun JVMs. The default is `true`. This protection is disabled if running on Java 9 onwards since the leak has been fixed for Java 9 onwards.
`ldapPoolProtection` | Enables protection so that the PoolCleaner thread started by `com.sun.jndi.ldap.LdapPoolManager` does not result in a memory leak. The thread is started the first time the `LdapPoolManager` class is used if the system property `com.sun.jndi.ldap.connect.pool.timeout` is set to a value greater than 0. Without this protection, if a web application uses this class the PoolCleaner thread will be configured with the thread's context class loader set to the web application class loader which in turn will trigger a memory leak on reload. Defaults to `true`. This protection is disabled if running on Java 9 onwards since the leak has been fixed for Java 9 onwards.
`securityLoginConfigurationProtection` | Enables protection so that usage of the `javax.security.auth.login.Configuration` class by a web application does not provoke a memory leak. The first access of this class will trigger the initializer that will retain a static reference to the context class loader. The protection loads the class with the system class loader to ensure that the static initializer is not triggered by a web application. Defaults to `true`. This protection is disabled if running on Java 8 onwards since the leak has been fixed for Java 8 onwards.
`securityPolicyProtection` | Enables protection so that usage of the deprecated `javax.security.auth.Policy` class by a web application does not result in a memory leak. The first access of this class will trigger the static initializer that will retain a static reference to the context class loader. The protection calls the `getPolicy()` method of this class to ensure that the static initializer is not triggered by a web application. Defaults to `true`. Note: The underlying leak has been fixed in Java 7 update 51 onwards and Java 8 onwards. This protection is therefore disabled if running on Java 8 onwards.
`tokenPollerProtection` | Enables protection so that any token poller thread initialized by `sun.security.pkcs11.SunPKCS11.initToken()` does not result in a memory leak. The thread is started depending on various conditions as part of the initialization of the Java Cryptography Architecture. Without the protection this can happen during Webapp deployment when the MessageDigest for generating session IDs is initialized. As a result the thread has the Webapp class loader as its thread context class loader. Enabling the protection initializes JCA early during Tomcat startup. Defaults to `true`. This protection is disabled if running on Java 9 onwards since the leak has been fixed for Java 9 onwards.
`urlCacheProtection` | Enables protection so that reading resources from JAR files using `java.net.URLConnection`s does not result in the JAR file being locked. Note that enabling this protection disables caching by default for all resources obtained via `java.net.URLConnection`s. Caching may be re-enabled on a case by case basis as required. Defaults to `true`.
`xmlParsingProtection` | Enables protection so that parsing XML files within a web application does not result in a memory leak. Note that memory profilers may not display the GC root associated with this leak making it particularly hard to diagnose. Defaults to `true`. This protection is disabled if running on Java 9 onwards since the leak has been fixed for Java 9 onwards.

#### JreMemoryLeakPreventionListener Examples

The following is an example of how to configure the `classesToInitialize` attribute of this listener.

If this listener was configured in server.xml as:

      <Listener className="org.apache.catalina.core.JreMemoryLeakPreventionListener"
                classesToInitialize="oracle.jdbc.driver.OracleTimeoutThreadPerVM" />

then the `OracleTimeoutThreadPerVM` class would be loaded and initialized during listener startup instead of during request processing.

#### Security Lifecycle Listener - org.apache.catalina.security.SecurityListener

The Security Lifecycle Listener performs a number of security checks when Tomcat starts and prevents Tomcat from starting if they fail. The listener is not enabled by default. To enabled it uncomment the listener in $CATALINA_BASE/conf/server.xml. For Tomcat versions before 8.5.30, if the operating system supports umask then the line in $CATALINA_HOME/bin/catalina.sh that obtains the umask also needs to be uncommented. For Tomcat 8.5.30 and later, the umask is automatically passed-into Tomcat.

This listener must only be nested within Server elements.

The following additional attributes are supported by the Security Lifecycle Listener:

Attribute | Description
--- | ---
`checkedOsUsers` | A comma separated list of OS users that must not be used to start Tomcat. If not specified, the default value of root is used. To disable this check, set the attribute to the empty string. Usernames are checked in a case-insensitive manner.
`minimumUmask` | The least restrictive umask that must be configured before Tomcat will start. If not specified, the default value of 0007 is used. To disable this check, set the attribute to the empty string. The check is not performed on Windows platforms.

#### StoreConfig Lifecycle Listener - org.apache.catalina.storeconfig.StoreConfigLifecycleListener

The StoreConfig Lifecycle Listener configures a StoreConfig MBean that may be used to save the current server configuration in server.xml or the current configuration for a web application in a context.xml file.

This listener must only be nested within Server elements.

The following additional attributes are supported by the StoreConfig Lifecycle Listener:

Attribute | Description
--- | ---
`storeConfigClass` | The name of the `IStoreConfig` implementation to use. If not specified the default of `org.apache.catalina.storeconfig.StoreConfig` will be used.
`storeRegistry` | The URL of the configuration file that configures how the `IStoreConfig` is to save the configuration. If not specified the built in resource `/org/apache/catalina/storeconfig/server-registry.xml` will be used.

#### ThreadLocal Leak Prevention Listener - org.apache.catalina.core.ThreadLocalLeakPreventionListener

The ThreadLocal Leak Prevention Listener triggers the renewal of threads in Executor pools when a Context is being stopped to avoid thread-local related memory leaks. Active threads will be renewed one by one when they come back to the pool after executing their task. The renewal happens only for contexts that have their `renewThreadsWhenStoppingContext` attribute set to `true`.

This listener must only be nested within Server elements.

No additional attributes are supported by the ThreadLocal Leak Prevention Listener.

#### UserConfig - org.apache.catalina.startup.UserConfig

The UserConfig provides feature of User Web Applications. User Web Applications map a request URI starting with a tilde character ("~") and a username to a directory (commonly named public_html) in that user's home directory on the server.

See the User Web Applications special feature on the Host element for more information.

The following additional attributes are supported by the UserConfig:

Attribute | Description
--- | ---
`directoryName` | The directory name to be searched for within each user home directory. The default is `public_html`.
`userClass` | The class name of the user database class. There are currently two user database, the `org.apache.catalina.startup.PasswdUserDatabase` is used on a Unix system that uses the /etc/passwd file to identify valid users. The `org.apache.catalina.startup.HomesUserDatabase` is used on a server where /etc/passwd is not in use. HomesUserDatabase deploy all directories found in a specified base directory.
`homeBase` | The base directory containing user home directories. This is effective only when `org.apache.catalina.startup.HomesUserDatabase` is used.
`allow` | A regular expression defining user who deployment is allowed. If this attribute is specified, the user to deploy must match for this pattern. If this attribute is not specified, all users will be deployed unless the user matches a deny pattern.
`deny` | A regular expression defining user who deployment is denied. If this attribute is specified, the user to deploy must not match for this pattern. If this attribute is not specified, deployment of user will be governed by a allow attribute.

#### Version Logging Lifecycle Listener - org.apache.catalina.startup.VersionLoggerListener

The Version Logging Lifecycle Listener logs Tomcat, Java and operating system information when Tomcat starts.

This listener must only be nested within Server elements and should be the first listener defined.

The following additional attributes are supported by the Version Logging Lifecycle Listener:

Attribute | Description
--- | ---
`logArgs` | If `true`, the command line arguments passed to Java when Tomcat started will be logged. If not specified, the default value of `true` will be used.
`logEnv` | If `true`, the current environment variables when Tomcat starts will be logged. If not specified, the default value of `false` will be used.
`logProps` | If `true`, the current Java system properties will be logged. If not specified, the default value of `false` will be used.

### Additional Implementations

#### System property replacement - org.apache.catalina.util.SystemPropertyReplacerListener

This listener performs system property replacement using the property source configured on the digester. When `${parameter}` denoted parameters are found in the values of system properties, the property source will be invoked to attempt to replace it.