# expiringmap

**Repository Path**: chenfei66/expiringmap

## Basic Information

- **Project Name**: expiringmap
- **Description**: No description available
- **Primary Language**: Unknown
- **License**: Apache-2.0
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2025-09-02
- **Last Updated**: 2025-09-02

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

# ExpiringMap

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A high performance, low-overhead, zero dependency, thread-safe [ConcurrentMap](https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentMap.html) implementation that expires entries. Features include:

* [Expiration policies](#expiration-policies)
* [Variable expiration](#variable-expiration)
* [Maximum size](#maximum-size)
* [Expiration listeners](#expiration-listeners)
* [Lazy entry loading](#lazy-entry-loading)
* [Expiration Introspection](#expiration-introspection)

Supports Java 6+ though the documentation uses lambdas for simplicity.

## Usage

ExpiringMap allows you to create a map that expires entries after a certain time period or when a maximum map size has been exceeded:

```java
Map<String, Connection> map = ExpiringMap.builder()
  .maxSize(123)
  .expiration(30, TimeUnit.SECONDS)
  .build();
  
// Expires after 30 seconds or as soon as a 124th element is added and this is the next one to expire based on the expiration policy
map.put("connection", connection);
```

#### Expiration Policies

Expiration can occur based on an entry's creation time or last access time:

```java
Map<String, Connection> map = ExpiringMap.builder()
  .expirationPolicy(ExpirationPolicy.ACCESSED)
  .build(); 
```

We can also specify an expiration policy for individual entries:

```java
map.put("connection", connection, ExpirationPolicy.CREATED);
```

And we can change policies on the fly:

```java
map.setExpirationPolicy("connection", ExpirationPolicy.ACCESSED);
```

#### Variable Expiration
        
Entries can have individually variable expiration times and policies:

```java
ExpiringMap<String, Connection> map = ExpiringMap.builder()
  .variableExpiration()
  .build();

map.put("connection", connection, ExpirationPolicy.ACCESSED, 5, TimeUnit.MINUTES);
```

Expiration times and policies can also be changed on the fly:

```java
map.setExpiration(connection, 5, TimeUnit.MINUTES);
map.setExpirationPolicy(connection, ExpirationPolicy.ACCESSED);
```

#### Maximum size

Expiration can also occur based on the number of entries in the map exceeding the allowed maximum size. Once this size
has been reached, adding an additional entry will expire the first entry in line for expiration based on the expiration policy.

```java
Map<String, Connection> map = ExpiringMap.builder()
  .maxSize(123)
  .build(); 
```

#### Expiration Listeners

Expiration listeners can be notified when an entry expires:

```java
Map<String, Connection> map = ExpiringMap.builder()
  .expirationListener((key, connection) -> connection.close())
  .build();
```

Expiration listeners are called synchronously as entries expire, and write operations to the map are blocked until the listeners complete. Asynchronous expiration listeners can also be configured and are called in a separate thread pool without blocking map operations:

```java
Map<String, Connection> map = ExpiringMap.builder()
  .asyncExpirationListener((key, connection) -> connection.close())
  .build();
```

Expiration listeners can also be added and removed on the fly:

```java
ExpirationListener<String, Connection> connectionCloser = (key, connection) -> connection.close();
map.addExpirationListener(connectionCloser);
map.removeExpirationListener(connectionCloser);
```

#### Lazy Entry Loading

Entries can be lazily loaded via an `EntryLoader` when `ExpiringMap.get` is called:

```java
Map<String, Connection> connections = ExpiringMap.builder()
  .expiration(10, TimeUnit.MINUTES)
  .entryLoader(address -> new Connection(address))
  .build();
  
// Loads a new connection into the map via the EntryLoader
connections.get("jodah.net");
```

Lazily loaded entries can also be made to expire at varying times:

```java
Map<String, Connection> connections = ExpiringMap.builder()
  .expiringEntry(address -> new ExpiringValue(new Connection(address), 5, TimeUnit.MINUTES))
  .build();
```

#### Expiration Introspection

ExpiringMap allows you to learn when an entry is expected to expire:

```java
long expiration = map.getExpectedExpiration("jodah.net");
```

We can also reset the internal expiration timer for an entry:

```java
map.resetExpiration("jodah.net");
```

And we can learn the configured expiration for individual entries:

```java
map.getExpiration("jodah.net");
```

## Additional Notes

#### On Variable Expiration

When variable expiration is disabled (default), `put` and `remove` operations have a constant *O(1)* time complexity. When variable expiration is enabled, `put` and `remove` operations have a time complexity of *O(log n)*.

#### On Google App Engine Integration

Google App Engine users must specify a `ThreadFactory` prior to constructing an `ExpiringMap` instance in order to avoid runtime permission errors:

```java

ExpiringMap.setThreadFactory(com.google.appengine.api.ThreadManager.currentRequestThreadFactory());
ExpiringMap.create();
```

See the [GAE docs on threads](https://cloud.google.com/appengine/docs/java/runtime#threads) for more info.

## Additional Resources

* [Javadocs](https://jodah.net/expiringmap/javadoc)
* [Who's Using ExpiringMap](https://github.com/jhalterman/expiringmap/wiki/Who's-Using-ExpiringMap)

## License

Copyright Jonathan Halterman and friends. Released under the [Apache 2.0 license](http://www.apache.org/licenses/LICENSE-2.0.html).