## System Properties

### Table of Contents

- Introduction
- Property replacements
- Expression Language
- Specifications
- Logging
- JAR Scanning
- Websockets
- Other

### Introduction

The following sections list the system properties that may be set to modify the default Tomcat behaviour.

### Property replacements

Property | Description
--- | ---

`org.apache.tomcat.util.digester. PROPERTY_SOURCE`

Set this to a comma separated list of fully qualified name of classes that implement `org.apache.tomcat.util.IntrospectionUtils.PropertySource`. Required to have a public constructor with no arguments.

Use this to add a property source, that will be invoked when `${parameter:-default-value}` denoted parameters (with optional default values) are found in the XML files that Tomcat parses.

Property replacement from the specified property source on the JVM system properties can also be done using the `REPLACE_SYSTEM_PROPERTIES` system property.

`org.apache.tomcat.util.digester.ServiceBindingPropertySource` can be used to replace parameters from any Kubernetes service bindings that follows the servicebinding.io spec

`org.apache.tomcat.util.digester.EnvironmentPropertySource` can be used to replace parameters from the process' environment variables, e.g. injected ConfigMaps or Secret objects in container based systems like OpenShift or Kubernetes.

`org.apache.tomcat.util.digester.SystemPropertySource` does replacement with system properties. It is always enabled, but can also be specified as part of the property value.

`org.apache.tomcat.util.digester. REPLACE_SYSTEM_PROPERTIES` | Set this boolean system property to `true` to cause property replacement from the digester property source on the JVM system properties.

### Expression Language

Property | Description
--- | ---

`org.apache.el. GET_CLASSLOADER_USE_PRIVILEGED`

Controls whether the EL API classes make use of a privileged block to obtain the thread context class loader. When using the EL API within Apache Tomcat this does not need to be set as all calls are already wrapped in a privileged block further up the stack. It may be required if using the EL API under a SecurityManager outside of Apache Tomcat.

If not specified, the default of `false` will be used.

`org.apache.el.BeanELResolver. CACHE_SIZE` | The number of jakarta.el.BeanELResolver.BeanProperties objects that will be cached by the EL Parser. If not specified, the default of `1000` will be used.
`org.apache.el.ExpressionBuilder. CACHE_SIZE` | The number of parsed EL expressions that will be cached by the EL Parser. If not specified, the default of `5000` will be used.

`org.apache.el.parser. COERCE_TO_ZERO`

If `true`, when coercing `null`s to objects of type Number, Character or Boolean the result will be `0` for Number and Character types and `false` for Boolean as required by the EL 2.2 and earlier specifications. If this property is `false` the result of the coercion will be `null` as required by the EL 3.0 specification.

If not specified, the default value of `false` will be used.

`org.apache.el.parser. SKIP_IDENTIFIER_CHECK` | If `true`, when parsing expressions, identifiers will not be checked to ensure that they conform to the Java Language Specification for Java identifiers. If not specified, the default value of `false` will be used.

### Specifications

Property | Description
--- | ---

`org.apache.catalina. STRICT_SERVLET_COMPLIANCE`

The default value of this system property is `false`.

If this is `true` the default values will be changed to `true` instead of `false` for:

- The `alwaysAccessSession` attribute of any Context element.
- The `contextGetResourceRequiresSlash` attribute of any Context element.
- The `dispatcherWrapsSameObject` attribute of any Context element.
- The `resourceOnlyServlets` attribute of any Context element.
- The `tldValidation` attribute of any Context element.
- The `useRelativeRedirects` attribute of any Context element.
- The `xmlNamespaceAware` attribute of any Context element.
- The `xmlValidation` attribute of any Context element.
- The `sessionActivityCheck` attribute of any Manager element.
- The `sessionLastAccessAtStart` attribute of any Manager element.

### Logging

Property | Description
--- | ---

`org.apache.juli.formatter`

If no logging configuration file is specified and no logging configuration class is specified using the `java.util.logging.config.class` and `java.util.logging.config.file` properties the default logging framework `org.apache.juli` will use the default `java.util.logging.SimpleFormatter` for all console output. To simply override the console output formatter, one can use the described property. Example: `-Dorg.apache.juli.formatter=org.apache.juli.OneLineFormatter`

`org.apache.juli. AsyncMaxRecordCount`

The maximum number of log records that the JULI AsyncFileHandler will queue in memory. New records are added to the queue and get asynchronously removed from the queue and written to the files by a single writer thread. When the queue is full and a new record is being logged the log record will be handled based on the `org.apache.juli.AsyncOverflowDropType` setting.

The default value is `10000` records. This number represents the global number of records, not on a per handler basis.

`org.apache.juli. AsyncOverflowDropType`

When the queue of log records of the JULI AsyncFileHandler is full, new log records are handled according to the following setting:

- `1` - the newest record in the queue will be dropped and not logged
- `2` - the oldest record in the queue will be dropped and not logged
- `3` - suspend the logging thread until older records got written to the log file and the queue is no longer full. This is the only setting that ensures that no messages get lost.
- `4` - drop the current log record

The default value is `1` (drop the newest record in the queue).

`org.apache.juli.logging. UserDataHelper.CONFIG`

The type of logging to use for errors generated by invalid input data. The options are: `DEBUG_ALL`, `INFO_THEN_DEBUG`, `INFO_ALL` and `NONE`. When `INFO_THEN_DEBUG` is used, the period for which errors are logged at DEBUG rather than INFO is controlled by the system property `org.apache.juli.logging.UserDataHelper.SUPPRESSION_TIME`.

The default value is `INFO_THEN_DEBUG`.

The errors currently logged using this system are:

- invalid cookies;
- invalid parameters;
- too many headers, too many parameters (hitting `maxHeaderCount` or `maxParameterCount` limits of a connector).
- invalid host names
- HTTP/2 stream closures

Other errors triggered by invalid input data may be added to this system in later versions.

`org.apache.juli.logging. UserDataHelper.SUPPRESSION_TIME`

When using `INFO_THEN_DEBUG` for `org.apache.juli.logging.UserDataHelper.CONFIG` this system property controls how long messages are logged at DEBUG after a message has been logged at INFO. Once this period has elapsed, the next message will be logged at INFO followed by a new suppression period where messages are logged at DEBUG and so on. The value is measured in seconds.

A value of `0` is equivalent to using `INFO_ALL` for `org.apache.juli.logging.UserDataHelper.CONFIG`.

A negative value means an infinite suppression period.

The default value is `86400` (24 hours).

### JAR Scanning

Property | Description
--- | ---
`tomcat.util.scan. StandardJarScanFilter.jarsToSkip` | A list of comma-separated file name patterns that is used as the default value for `pluggabilitySkip` and `tldSkip` attributes of the standard JarScanFilter implementation. The coded default is empty, however the system property is set in a default Tomcat installation via the `$CATALINA_BASE/conf/catalina.properties` file.
`tomcat.util.scan. StandardJarScanFilter.jarsToScan` | A list of comma-separated file name patterns that is used as the default value for `pluggabilityScan` and `tldScan` attributes of the standard JarScanFilter implementation. The coded default is empty, however the system property is set in a default Tomcat installation via the `$CATALINA_BASE/conf/catalina.properties` file.

### Websockets

Property | Description
--- | ---
`org.apache.tomcat. websocket.DEFAULT_BUFFER_SIZE` | The default size for buffers used in the Websockets container. The default value is `8192` which corresponds to 8KB.
`org.apache.tomcat. websocket.DEFAULT_ORIGIN_HEADER_VALUE` | Default value of the origin header that will be sent by the client during the upgrade handshake. The default is null so that no origin header is sent.
`org.apache.tomcat. websocket.DEFAULT_PROCESS_PERIOD` | The number of periodic ticks between periodic processing which involves in particular session expiration checks. The default value is `10` which corresponds to 10 seconds.

### Other

Property | Description
--- | ---
`catalina.useNaming` | If this is `false` it will override the `useNaming` attribute for all Context elements.
`javax.sql.DataSource.Factory` | The class name of the factory to use to create resources of type `javax.sql.DataSource`. If not specified the default of `org.apache.tomcat.dbcp.dbcp2.BasicDataSourceFactory` is used which is a package renamed (to avoid conflicts) copy of Apache Commons DBCP 2.
`jakarta.mail.Session.Factory` | The class name of the factory to use to create resources of type `jakarta.mail.Session`. If not specified the default of `org.apache.naming.factory.MailSessionFactory` is used.
`catalina.config` | The location from which to load the catalina.properties configuration file. This may be an absolute URL, a relative (to the current working directory) URL or an alternative file name in which case Tomcat will attempt to load the file from the default location of `$CATALINA_BASE/conf/`.
`tomcat.util.buf.StringCache.byte.enabled` | If `true`, the String cache is enabled for `ByteChunk`. If not specified, the default value of `false` will be used.
`tomcat.util.buf.StringCache.char.enabled` | If `true`, the String cache is enabled for `CharChunk`. If not specified, the default value of `false` will be used.
`tomcat.util.buf.StringCache.trainThreshold` | The number of times `toString()` must be called before the cache is activated. If not specified, the default value of `20000` will be used.
`tomcat.util.buf.StringCache.cacheSize` | The size of the String cache. If not specified, the default value of `200` will be used.
`org.apache.tomcat.util.buf.UriUtil. WAR_SEPARATOR` | The character to use to separate the WAR file and WAR content parts of a WAR URL using the custom WAR scheme provided by Tomcat. This is equivalent to how `!` is used in JAR URLs. If not specified, the default value of `*` will be used.
`tomcat.util.buf.StringCache.maxStringSize` | The maximum length of String that will be cached. If not specified, the default value of `128` will be used.
`org.apache.tomcat.util. http.FastHttpDateFormat.CACHE_SIZE` | The size of the cache to use parsed and formatted date value. If not specified, the default value of `1000` will be used.
`org.apache.catalina.startup. EXIT_ON_INIT_FAILURE` | If `true`, the server will exit if an exception happens during the server initialization phase. To support this feature, this system property is used as the default for the throwOnFailure attribute of a Connector. If not specified, the default value of `false` will be used.
`org.apache.catalina.startup. RealmRuleSet.MAX_NESTED_REALM_LEVELS` | The CombinedRealm allows nested Realms. This property controls the maximum permitted number of levels of nesting. If not specified, the default value of `3` will be used.
`org.apache.catalina.startup. CredentialHandlerRuleSet.MAX_NESTED_LEVELS` | The NestedCredentialHandler allows nested CredentialHandlers. This property controls the maximum permitted number of levels of nesting. If not specified, the default value of `3` will be used.
`org.apache.catalina.tribes.io. BufferPool.DEFAULT_POOL_SIZE` | The size of the buffer pool which is used by Tribes in bytes. If not specified, the default value of `100*1024*1024` (100MB) will be used.