Cache Chilkat2 Java Reference Documentation

Cache

Current Version: 11.7.0

Markdown version of this page for AI tools (v 11.7.0) · all AI docs

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Chilkat.Cache

Store, retrieve, expire, and clean up cached text or binary data on disk.

Chilkat.Cache is a disk-based cache class for storing and retrieving text or binary items by unique key. It provides configurable cache roots, optional multi-level directory layout, expiration metadata, ETag metadata, cache lookup, fetch-status properties, expiration updates, and cleanup methods for deleting individual items, expired items, older items, or the entire cache.

Key-based storage

Store and retrieve cached items by unique key, without the application needing to manage the underlying cache filenames directly.

Text and binary data

Cache strings, byte data, files, or Chilkat buffer objects depending on the data form used by the application.

Expiration control

Associate cached items with expiration times, update expiration metadata, and check whether cached content is still usable.

ETag metadata

Store and retrieve ETag values for workflows that need HTTP-style cache validation or conditional re-fetch logic.

Configurable layout

Choose the cache root directory and use an optional multi-level directory structure to avoid too many files in a single folder.

Cleanup operations

Delete a single cached item, remove expired items, remove older items, or clear the entire cache when needed.

Common pattern: Configure the cache root, choose the key used to identify each item, check whether a valid cached copy exists, fetch or regenerate the content when needed, store it with expiration and optional ETag metadata, and periodically clean up expired or old cached items.

For an extended overview, see Cache Class Overview.

Object Creation

import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.Cache;

try (Cache cache = new Cache()) {
    // ... use cache ...
} catch (ChilkatException e) {
    System.out.println(e.getMessage());          // "Cache.someMethod failed: <reason>"
    System.out.println(e.getLastErrorText());    // the full log of the failed call
}
public Cache()

Creates the underlying native Chilkat object. The native library (chilkat2java) is loaded the first time any Chilkat2 object is created; see the README in the download for where it is looked for (-Dchilkat2.library.path, a classpath resource, or java.library.path).

public void close()

Releases the native object (Cache is AutoCloseable, so try-with-resources calls it). Calling it again does nothing; any other method or property accessor called afterwards throws IllegalStateException. An object that is never closed is freed by a background cleaner once it becomes unreachable, but the garbage collector does not see native memory, so closing is the normal path. Objects returned by methods are owned by the caller too.

public boolean isClosed()

Returns true once close() has been called.

Errors

A method that fails throws ChilkatException, an unchecked exception carrying getClassName(), getMethodName(), getReason() (one line, also in the message) and getLastErrorText() (the full log, captured at the moment of the failure). The object remains usable. Methods that look something up and find nothing return null instead of throwing (each such method says so), and methods that answer a question (hasMember, isUnlocked, ...) return a plain boolean. Property accessors do not throw for Chilkat reasons.

A null string or object argument throws NullPointerException naming the parameter (except where a method documents that null is accepted), and a string containing U+0000 throws IllegalArgumentException.

Use an object from one thread at a time; it may be handed from one thread to another. The one cross-thread operation is setting setAbortCurrent(true) on an object that is busy in another thread (on the classes that have AbortCurrent). Unlocking: call new Global().unlockBundle("...") once at startup.

Properties

DebugLogFilePath
// read/write
String getDebugLogFilePath()
void setDebugLogFilePath(String value)

If set to a file path, this property logs the LastErrorText of each Chilkat method or property call to the specified file. This logging helps identify the context and history of Chilkat calls leading up to any crash or hang, aiding in debugging.

Enabling the VerboseLogging property provides more detailed information. This property is mainly used for debugging rare instances where a Chilkat method call causes a hang or crash, which should generally not happen.

Possible causes of hangs include:

  • A timeout property set to 0, indicating an infinite timeout.
  • A hang occurring within an event callback in the application code.
  • An internal bug in the Chilkat code causing the hang.

More Information and Examples
Example showing how to use DebugLogFilePath.
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LastErrorHtml
// read-only
String getLastErrorHtml()

Provides HTML-formatted information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.

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LastErrorText
// read-only
String getLastErrorText()

Provides plain text information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.

More Information and Examples
Concept of LastErrorTextLastErrorText Standard Information
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LastErrorXml
// read-only
String getLastErrorXml()

Provides XML-formatted information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.

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LastEtagFetched
// read-only
String getLastEtagFetched()

Returns the ETag metadata associated with the most recently fetched cache item. An empty string means that the fetched item has no stored ETag.

Read after a fetch: This property describes the item returned by the most recent successful fetch operation, such as FetchBd, FetchSb, or FetchText.
ETags are opaque metadata: The cache stores and returns the string but does not interpret it. Applications commonly use an HTTP ETag with conditional requests such as If-None-Match.

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LastExpirationFetchedStr
// read-only
String getLastExpirationFetchedStr()

Returns the expiration date and time stored for the most recently fetched cache item, formatted as an RFC 822-style Internet date. An empty string represents an item with no expiration date.

Expiration is metadata: Fetching an expired item is still possible. Read LastHitExpired after the fetch to determine whether the returned entry is stale.

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LastHitExpired
// read-only
boolean getLastHitExpired()

Returns true when the expiration time of the most recently fetched item is earlier than the current system date and time; otherwise returns false.

Expired does not mean deleted: Expiration marks an entry as stale. The file remains in the cache until it is replaced or removed by methods such as DeleteAllExpired or DeleteFromCache.

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LastKeyFetched
// read-only
String getLastKeyFetched()

Returns the application-defined key associated with the most recently fetched cache item.

Keys are not limited to URLs: A canonicalized URL is a common key for cached web content, but any unique string may be used. Reusing a key causes a save operation to replace the existing item for that key.

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LastMethodSuccess
// read/write
boolean getLastMethodSuccess()
void setLastMethodSuccess(boolean value)

Indicates the success or failure of the most recent method call: true means success, false means failure. This property remains unchanged by property setters or getters. This method is present to address challenges in checking for null or Nothing returns in certain programming languages. Note: This property does not apply to methods that return integer values or to boolean-returning methods where the boolean does not indicate success or failure.

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Level
// read/write
int getLevel()
void setLevel(int value)

Gets or sets the number of directory levels used beneath each cache root. Valid values are 0, 1, and 2.

ValueDirectory layout
0All cache files are stored directly in the cache root.
1Files are distributed among 256 first-level directories named 0 through 255.
2Files are distributed through two levels of 256 directories, allowing as many as 65,536 leaf directories per root.
Configure before use: Use the same level when reopening an existing cache. Changing the layout does not reorganize previously stored files and can prevent the object from locating them through their keys.

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NumRoots
// read-only
int getNumRoots()

Returns the number of cache-root directories that have been registered by calling AddRoot.

Multiple roots: A cache may span more than one directory or storage device. Configure the same root set when reopening a persistent cache so previously stored items remain discoverable.

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VerboseLogging
// read/write
boolean getVerboseLogging()
void setVerboseLogging(boolean value)

If set to true, then the contents of LastErrorText (or LastErrorXml, or LastErrorHtml) may contain more verbose information. The default value is false. Verbose logging should only be used for debugging. The potentially large quantity of logged information may adversely affect peformance.

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Version
// read-only
String getVersion()

Version of the component/library, such as "10.1.0"

More Information and Examples
How to get the Chilkat version at runtime.
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Methods

AddRoot
void addRoot(String path)

Adds path as a root directory for the disk cache. Call this method once for each root that should participate in the cache.

For example, a cache distributed across D:\cacheRoot, E:\cacheRoot, and F:\cacheRoot is configured by calling this method three times.

Use dedicated writable directories: Cache cleanup methods can delete cache files beneath every configured root. Do not mix unrelated application files into a cache root.
Persistent configuration: Recreate the same roots and Level setting before accessing a cache created by an earlier process or application run.
More Information and Examples
Large Persistent Hash Table Stored on Filesystem
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DeleteAll
int deleteAll()

Deletes every cache item from all configured roots and returns the number of cache files removed. Multi-level subdirectories are retained.

Destructive operation: This cannot be limited to a key prefix or reversed. Use cache roots dedicated to Chilkat cache data.
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DeleteAllExpired
int deleteAllExpired()

Deletes all cache items whose stored expiration time is earlier than the current system time and returns the number of files removed.

Non-expiring entries remain: Items saved without an expiration date are not removed by this method.
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DeleteFromCache
void deleteFromCache(String key)

Deletes the cache item identified by key.

Return valueMeaning
trueThe item was deleted, or no item existed for the key.
falseThe item exists but could not be deleted, for example because of a filesystem permission or sharing error.
Idempotent deletion: A missing key is not treated as an error, which makes it safe to call this method when the application merely wants to ensure that an item is absent.

Throws ChilkatException on failure; e.getLastErrorText() (or the object's getLastErrorText()) explains why, and the object remains usable.

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DeleteOlderDt
int deleteOlderDt(DateTime dt)

Deletes cache items older than the cutoff date and time supplied in dt.

Returns the number of cache files deleted, or -1 if an error occurs.

Different from expiration cleanup: Use DeleteAllExpired when the decision should be based specifically on each item's expiration metadata.
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DeleteOlderStr
int deleteOlderStr(String dateTimeStr)

Deletes cache items older than the cutoff date and time supplied in dateTimeStr as an RFC 822-style Internet date string.

Returns the number of cache files deleted, or -1 if an error occurs.

Date format: A typical value is Mon, 03 Aug 2026 12:00:00 GMT. Use DeleteOlderDt when the cutoff is already available as a CkDateTime.
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FetchBd
void fetchBd(String key, BinData bd)
Introduced in version 9.5.0.91

Retrieves the binary item identified by key and loads its bytes into the BinData object supplied in bd.

The key is application-defined, may contain any characters, and must uniquely identify the intended item.

Check the return value: Use the destination only when this method returns true. A failed lookup or filesystem error returns false.
Freshness: A successful fetch may return an expired item. Read LastHitExpired immediately afterward when stale data must not be used.

Throws ChilkatException on failure; e.getLastErrorText() (or the object's getLastErrorText()) explains why, and the object remains usable.

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FetchSb
void fetchSb(String key, StringBuilder sb)
Introduced in version 9.5.0.91

Retrieves the text item identified by key and loads its content into the StringBuilder supplied in sb.

The key is application-defined, may contain any characters, and must uniquely identify the intended item.

Check the return value: Use the destination only when this method returns true. A failed lookup or filesystem error returns false.
Freshness: A successful fetch may return an expired item. Read LastHitExpired immediately afterward when stale data must not be used.

Throws ChilkatException on failure; e.getLastErrorText() (or the object's getLastErrorText()) explains why, and the object remains usable.

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FetchText
String fetchText(String key)

Retrieves the text item identified by key and returns its string content.

The key is application-defined, may contain any characters, and must uniquely identify the intended item.

Freshness is separate: A successful fetch can return an expired entry. Read LastHitExpired immediately afterward when the application requires only fresh data.

Throws ChilkatException on failure; e.getLastErrorText() (or the object's getLastErrorText()) explains why, and the object remains usable.

More Information and Examples
Large Persistent Hash Table Stored on Filesystem
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GetEtag
String getEtag(String key)

Returns the ETag metadata stored with the cache item identified by key.

Opaque value: Chilkat does not parse or validate the ETag. An application may store any auxiliary string here, although HTTP entity tags are the common use case.

Throws ChilkatException on failure; e.getLastErrorText() (or the object's getLastErrorText()) explains why, and the object remains usable.

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GetExpirationStr
String getExpirationStr(String url)

Returns the expiration date and time stored for the item identified by url, formatted as an RFC 822-style Internet date string.

Argument name: Some language bindings name url url for historical reasons. It is the cache key and does not need to be a URL.
No-expiration entries: An empty stored expiration represents an item that does not expire automatically.

Throws ChilkatException on failure; e.getLastErrorText() (or the object's getLastErrorText()) explains why, and the object remains usable.

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GetFilename
String getFilename(String key)

Returns the absolute filesystem path of the cache file associated with key.

Implementation detail: Treat the returned path as diagnostic information. Applications should normally read, update, and delete entries through the Cache API rather than modifying cache files directly.

Throws ChilkatException on failure; e.getLastErrorText() (or the object's getLastErrorText()) explains why, and the object remains usable.

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GetRoot
String getRoot(int index)

Returns the directory path of the cache root at zero-based index. Valid indexes range from 0 through NumRoots - 1.

Throws ChilkatException on failure; e.getLastErrorText() (or the object's getLastErrorText()) explains why, and the object remains usable.

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IsCached
boolean isCached(String key)

Returns true if an item exists for key, or false if the key is not present.

Presence is not freshness: This method does not imply that the entry is unexpired. Fetch the item and examine LastHitExpired, or read its expiration metadata, when freshness matters.

Never throws: false is an answer, not a failure.

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SaveBd
void saveBd(String key, String expiration, String etag, BinData bd)
Introduced in version 11.0.0

Stores the contents of bd as binary cache data under key. If the key already exists, its data and metadata are replaced.

ArgumentPurpose
keyThe unique application-defined cache key.
expirationExpiration as an RFC 822-style Internet date string. Pass an empty string for no expiration.
etagOptional ETag or application metadata. Pass an empty string when unused.
bdThe BinData containing the bytes to save.
Expiration is not automatic deletion: An expired item remains present until it is replaced or explicitly removed. This permits stale-while-revalidate workflows but requires the application to check freshness.

Throws ChilkatException on failure; e.getLastErrorText() (or the object's getLastErrorText()) explains why, and the object remains usable.

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SaveTextDt
void saveTextDt(String key, DateTime expireDateTime, String eTag, String itemTextData)

Stores itemTextData as a text cache item under key, with the expiration date and time supplied in expireDateTime. If the key already exists, its data and metadata are replaced.

eTag is optional ETag or application metadata and may be an empty string. The key may contain any characters and may be any length, but it must uniquely identify the item.

Expiration does not delete: After the expiration time passes, the entry remains on disk and can still be fetched. Use LastHitExpired to detect staleness and a deletion method to remove it.

Throws ChilkatException on failure; e.getLastErrorText() (or the object's getLastErrorText()) explains why, and the object remains usable.

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SaveTextNoExpire
void saveTextNoExpire(String key, String eTag, String itemTextData)

Stores itemTextData as a non-expiring text cache item under key. If the key already exists, its data and metadata are replaced.

eTag is optional ETag or application metadata and may be an empty string.

Throws ChilkatException on failure; e.getLastErrorText() (or the object's getLastErrorText()) explains why, and the object remains usable.

More Information and Examples
Large Persistent Hash Table Stored on Filesystem
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SaveTextStr
void saveTextStr(String key, String expireDateTime, String eTag, String itemTextData)

Stores itemTextData as a text cache item under key, with expireDateTime providing the expiration time as an RFC 822-style Internet date string. If the key already exists, its data and metadata are replaced.

eTag is optional ETag or application metadata and may be empty.

Date alternatives: Use SaveTextDt when the expiration is available as a CkDateTime, or SaveTextNoExpire for an entry without expiration.

Throws ChilkatException on failure; e.getLastErrorText() (or the object's getLastErrorText()) explains why, and the object remains usable.

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UpdateExpirationDt
void updateExpirationDt(String key, DateTime expireDateTime)

Replaces the expiration date and time of the cache item identified by key with the CkDateTime value supplied in expireDateTime. The cached data and ETag are unchanged.

Existing item required: This method updates metadata; it does not create a new cache entry when the key is absent.

Throws ChilkatException on failure; e.getLastErrorText() (or the object's getLastErrorText()) explains why, and the object remains usable.

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UpdateExpirationStr
void updateExpirationStr(String key, String expireDateTime)

Replaces the expiration date and time of the cache item identified by key with the RFC 822-style Internet date string supplied in expireDateTime. The cached data and ETag are unchanged.

Argument name: Some language bindings name key url; it is the cache key and does not need to be a URL. Use UpdateExpirationDt for a CkDateTime value.

Throws ChilkatException on failure; e.getLastErrorText() (or the object's getLastErrorText()) explains why, and the object remains usable.

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