如何阅读Chronicle队列中的最后N个记录？

我有以下代码从Chronicle队列中读取（它是用Kotlin编写的，但没关系）：

val queue = ChronicleQueueBuilder.single(path).build() val tailer = queue.createTailer() tailer.toEnd() // // This code is wrong // val lastIndex = tailer.index() // // val shift = lastIndex - 10 // if (shift > 0) { // tailer.moveToIndex(lastIndex) // } while (true) { val text = await(tailer) if (prefix == null) { println(text) } else { if (text.startsWith(prefix)) { // Would be nice without additional allocation ... println(text.substring(prefix.length + 1)) } } } 

如何修改注释的代码以从队列中读取前10条记录并继续？

基本原理：在队列用于显示日志的情况下，这很有用。 您希望看到一些以前的日志记录语句，并看到新的日志语句。

Answer 1

我为你写了一个测试。 请运行相同的应该工作。

 public class ChronicleTest { private String chroniclePath = "/tmp/chronicle-test"; private int msgCount = 10; private int i = 0; @Test public void writeToQ() { ChronicleQueue queue = ChronicleQueueBuilder.single(chroniclePath).build(); ExcerptAppender appender = queue.acquireAppender(); for (i = 1; i <= msgCount; i++) { appender.writeBytes(b -> { b.writeInt(i); }); } ExcerptTailer tailer = queue.createTailer(); tailer.toEnd(); long lastIndex = tailer.index(); tailer.moveToIndex(lastIndex - 5); while (tailer.readBytes(b -> { int value = b.readInt(); System.out.println("Received:" + value); })) System.out.println("Completed"); } } 

Answer 2

除了直接使用索引外，还可以使用ExcerptTailer的direction属性：

  final SingleChronicleQueue queue = createQueue(); final int totalRecords = 20; final int tailRecords = 10; final ExcerptAppender appender = queue.acquireAppender(); for (int i = 0; i < totalRecords; i++) { try(final DocumentContext ctx = appender.writingDocument()) { ctx.wire().writeText(Integer.toString(i)); } } final ExcerptTailer tailer = queue.createTailer(); tailer.direction(TailerDirection.BACKWARD).toEnd(); int rewind = tailRecords; final int endCycle = tailer.cycle(); while(--rewind != 0) { try(final DocumentContext ctx = tailer.readingDocument()) { if (!ctx.isPresent()) { break; } if (endCycle != tailer.cycle()) { System.out.println("Rewound past beginning of cycle"); } } } tailer.direction(TailerDirection.FORWARD); for (int i = 0; i < tailRecords; i++) { try(final DocumentContext ctx = tailer.readingDocument()) { if (!ctx.isPresent()) { break; } System.out.println(ctx.wire().readText()); } }