为什么 Postgres 复制流在单独的函数中使用时不起作用？

我正在研究 postgres 复制流 API。在处理它的过程中遇到了异常行为。

当我使用复制槽在主块内编写整个代码时，一切正常。

public class Server implements Config {

public static void main(String[] args) {
    Properties prop = new Properties();
    prop.load(new FileInputStream(System.getProperty("prop")));

    String user = prop.getProperty("user");
    String password = prop.getProperty("password");
    String url = prop.getProperty("url");

    Properties props = new Properties();
    PGProperty.USER.set(props, user);
    PGProperty.PASSWORD.set(props, password);
    PGProperty.ASSUME_MIN_SERVER_VERSION.set(props, "9.4");
    PGProperty.REPLICATION.set(props, "database");
    PGProperty.PREFER_QUERY_MODE.set(props, "simple");

    Connection conn= null;
    PGConnection replicationConnection= null;
    PGReplicationStream stream = null;

        conn = DriverManager.getConnection(url, props);
        replicationConnection = conn.unwrap(PGConnection.class);
        stream = replicationConnection.getReplicationAPI().replicationStream().logical()
                .withSlotName("replication_slot")
                .withSlotOption("include-xids", true)
                .withSlotOption("include-timestamp", "on")
                .withSlotOption("skip-empty-xacts", true)
                .withStatusInterval(20, TimeUnit.SECONDS).start();

    while (true) {
            ByteBuffer msg;
            try {
                msg = stream.readPending();         

            if (msg == null) {
                TimeUnit.MILLISECONDS.sleep(10L);
                continue;
            }

            int offset = msg.arrayOffset();
            byte[] source = msg.array();
            int length = source.length - offset;
            // convert byte buffer into string
            String data = new String(source, offset, length);

            // then convert it into bufferedreader
            BufferedReader reader = new BufferedReader(new StringReader(data));
            String line = reader.readLine();

            while (line != null) {
                System.out.println(line);
                line = reader.readLine();
            }
            stream.setAppliedLSN(stream.getLastReceiveLSN());
            stream.setFlushedLSN(stream.getLastReceiveLSN());
        } catch (SQLException | IOException | InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        }
}

但是当我尝试使用这样的单独方法分离流逻辑时

public class Server implements Config {

public static void main(String[] args) {
    PGReplicationStream stream = getReplicationStream();
        while (true) {
            ByteBuffer msg;
            try {
                msg = stream.readPending();
    if (msg == null) {
                TimeUnit.MILLISECONDS.sleep(10L);
                continue;
            }

            int offset = msg.arrayOffset();
            byte[] source = msg.array();
            int length = source.length - offset;
            String data = new String(source, offset, length);

            BufferedReader reader = new BufferedReader(new StringReader(data));
            String line = reader.readLine();

            while (line != null) {
                System.out.println(line);
                line = reader.readLine();
            }
            stream.setAppliedLSN(stream.getLastReceiveLSN());
            stream.setFlushedLSN(stream.getLastReceiveLSN());
        } catch (SQLException | IOException | InterruptedException e) {
            e.printStackTrace();
        }
        }

}
public static PGReplicationStream getReplicationStream() {
    Properties prop = new Properties();
    try {
        prop.load(new FileInputStream(System.getProperty("prop")));
    } catch (IOException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    }

    String user = prop.getProperty("user");
    String password = prop.getProperty("password");
    String url = prop.getProperty("url");

    Properties props = new Properties();
    PGProperty.USER.set(props, user);
    PGProperty.PASSWORD.set(props, password);
    PGProperty.ASSUME_MIN_SERVER_VERSION.set(props, "9.4");
    PGProperty.REPLICATION.set(props, "database");
    PGProperty.PREFER_QUERY_MODE.set(props, "simple");

    Connection conn= null;
    PGConnection replicationConnection= null;
    PGReplicationStream stream = null;
    try {
        conn = DriverManager.getConnection(url, props);
        replicationConnection = conn.unwrap(PGConnection.class);
        stream = replicationConnection.getReplicationAPI().replicationStream().logical()
                .withSlotName("replication_slot")
                .withSlotOption("include-xids", true)
                .withSlotOption("include-timestamp", "on")
                .withSlotOption("skip-empty-xacts", true)
                .withStatusInterval(20, TimeUnit.SECONDS).start();
    } catch (SQLException e) {
        e.printStackTrace();
    }
    return stream;
}

}

读取一些数据后，程序报错

org.postgresql.util.PSQLException: Database connection failed when reading from copy
at org.postgresql.core.v3.QueryExecutorImpl.readFromCopy(QueryExecutorImpl.java:1028)
at org.postgresql.core.v3.CopyDualImpl.readFromCopy(CopyDualImpl.java:41)
at org.postgresql.core.v3.replication.V3PGReplicationStream.receiveNextData(V3PGReplicationStream.java:155)
at org.postgresql.core.v3.replication.V3PGReplicationStream.readInternal(V3PGReplicationStream.java:124)
at org.postgresql.core.v3.replication.V3PGReplicationStream.readPending(V3PGReplicationStream.java:78)
at Server.main(Server.java:47)
Caused by: java.net.SocketException: Socket closed
at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
at java.net.SocketInputStream.read(SocketInputStream.java:171)
at java.net.SocketInputStream.read(SocketInputStream.java:141)
at org.postgresql.core.VisibleBufferedInputStream.readMore(VisibleBufferedInputStream.java:140)
at org.postgresql.core.VisibleBufferedInputStream.ensureBytes(VisibleBufferedInputStream.java:109)
at org.postgresql.core.VisibleBufferedInputStream.read(VisibleBufferedInputStream.java:191)
at org.postgresql.core.PGStream.receive(PGStream.java:495)
at org.postgresql.core.PGStream.receive(PGStream.java:479)
at org.postgresql.core.v3.QueryExecutorImpl.processCopyResults(QueryExecutorImpl.java:1161)
at org.postgresql.core.v3.QueryExecutorImpl.readFromCopy(QueryExecutorImpl.java:1026)
... 5 more

我认为这两种方法没有任何区别。但该程序的行为有所不同。有人可以解释一下第二种方法有什么问题吗？

我相信你的问题是Connection。一旦你的函数返回，它就会超出范围，并且由垃圾收集器来收集它并完成。在完成时，连接被关闭，然后你的程序可能会失败。尝试在主方法中可用的范围内移动连接和其他所需的中间变量，然后重试。