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The wiki pages are not used for documentation any more. Please visit http://bookkeeper.apache.org/docs/latest/api/overview/ for latest API documentation. |
(this page will contain a description of all the Client API of BookKeeper)
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try (BookKeeper bookkeeper = BookKeeper.forConfig(new ClientConfiguration()).build(); LedgerHandle ledger = bookkeeper.createLedger(BookKeeper.DigestType.CRC32, "foo".getBytes())) { ledger.addEntry("bar".getBytes()); } |
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In order to create a BookKeeper client you have to setup a ClientConfiguration object.
The most important parameter is the ZooKeeper connection string, which is needed to access to the BookKeeper ensemble.
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ClientConfiguration config = new ClientConfiguration(); config.setZkServers("localhost:1281"); try (BookKeeper bookKeeper = BookKeeper.forConfig(config).build();) { // ... } |
If you already have a ZooKeeper handle and you want to share it you have to pass it the Builder
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ZooKeeper zookeeper = ....; ClientConfiguration config = new ClientConfiguration(); config.setZkServers("localhost:1281"); try (BookKeeper bookKeeper = BookKeeper .forConfig(config) .setZookeeper(zookeeper) .build();) { // ... } |
Beware that ClientConfiguration will be automatically filled with System.getProperties()
Synch vs Asynch
BookKeeper API methods provide access to BookKeeper features, internally all is asynchronous and in general the asynch API will give you more control about whats going on and result in better performances.
(explanation of the existance of both a synch API and a asynch API)
For instance
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try (LedgerHandle handle = bookkeeper.createLedger(1, 1, 1, BookKeeper.DigestType.CRC32, "test".getBytes())) {
byte[] data = "test".getBytes();
final CountDownLatch la = new CountDownLatch(SIZE);
for (int i = 0; i < SIZE; i++) {
handle.asyncAddEntry(data, new AsyncCallback.AddCallback() {
@Override
public void addComplete(int rc, LedgerHandle lh, long l, Object o) {
if (rc != BKException.Code.OK) {
System.err.println("Error: "+BKException.getMessage(rc));
}
assertEquals("callback_param",o);
la.countDown();
}
}, "callback_param");
}
la.await();
} |
A similar code using the synch API is:
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try (LedgerHandle handle = bookkeeper.createLedger(1, 1, 1, BookKeeper.DigestType.CRC32, "test".getBytes())) {
byte[] data = "test".getBytes();
for (int i = 0; i < SIZE; i++) {
handle.addEntry(data);
}
} |
The async API will be really more efficient from the standpoint of speed but you have to deal with callbacks, remember that:
- callbacks are called in a different thread
- exception will not be thrown in the main (callee) thread but you have to switch over the 'rc' (return code) parameter, using the BKException.Code class or BKException.create(rc) method
- you have no direct control on the pool of threads which executes the callbacks
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Writing to a Ledger
Reading from a Ledger
(brief explanation of fencing)
Closing a Ledger
You always have to call LedgerHandle.close(), this operation will ensure the consistency of all metadata of the ledger and will release resources assigned to the ledger, both locally to the client and on Bookies.
Deleting a Ledger
When a Ledger is no more in use it is better to delete it, in order to let all the Bookies release all the resources retained by the ledger. A ledger will also retain resources on ZooKeeper.
The code is simple:
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bookkeeper.deleteLedger(id);
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List ledgers
If you need to discover all the ledgersyou can use the BookKeeperAdmin tool
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BookKeeperAdmin admin = new BookKeeperAdmin(bookkeeper);
for (long id : admin.listLedgers()) {
LedgerHandle h = admin.openLedgerNoRecovery(id);
LedgerMetadata meta = admin.getLedgerMetadata(h);
} |
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