Question

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

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))
        }
    }
}

如何修改注释代码以从队列中读取前10条记录并继续？

原理：在队列用于显示日志的情况下，它非常有用。您希望查看一些以前的日志记录语句，并查看新的日志记录语句。

Answer 1

我为你写了一个测试。请运行它应该工作。

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，您还可以使用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());
        }
    }

如何阅读Chronicle Queue的最后N条记录？

2 个答案: