抛出不可能的 NullPointerException

Question

在几年前写的一个网络服务器项目中，我偶尔会得到一个非常奇怪的 - 在我看来 - 不可能的NullPointerException. 它发生在用于在控制台上记录输出的实用方法中。这是该方法的错误摘录：try {    Encoder encoder = Base64.getEncoder();    if(logWriter != null) {        logWriter.write(String.valueOf(System.currentTimeMillis()));        logWriter.write(" ");        logWriter.write(String.valueOf(level));        logWriter.write(" ");        logWriter.write(encoder.encodeToString(Thread.currentThread().getName().getBytes()).replaceAll("(?:\\r\\n|\\n\\r|\\n|\\r)", ""));        logWriter.write(" ");        logWriter.write(encoder.encodeToString(log.getBytes()).replaceAll("(?:\\r\\n|\\n\\r|\\n|\\r)", ""));        logWriter.write("\r\n");        logWriter.flush();    }    lastWriterActivity = System.currentTimeMillis();} catch (IOException e) {    println("Failed to write log to file: " + e, Color.RED);    try {        logWriter.close();    } catch (IOException e1) {        println("### Possible resource leak; unable to close log writer", Color.RED);    }    logWriter = null;}哪里logWriter是BufferedWriter. NPE 在第一个catch块调用中抛出logWriter.close()。但是：当我的 logWriter 是 时IOException，我的try块中怎么会被抛出!= null？Base64.getEncoder()不能抛出 anIOException并且没有其他代码要执行。这是我的堆栈跟踪：Exception in thread "connection_0:0:0:0:0:0:0:1@1544725509" java.lang.NullPointerExceptionat org.jpuzzle.main.Logger.write(Logger.java:347)at org.jpuzzle.main.Logger.verbose(Logger.java:187)at org.jpuzzle.protocol.http.HttpRequest.onRequest(HttpRequest.java:1090)at org.jpuzzle.network.ConnectionListener$Connection.proceed(ConnectionListener.java:438)at org.jpuzzle.network.ConnectionListener$Connection.run(ConnectionListener.java:408)我的方法是synchronized，所以互斥应该没有困难，我不知道为什么会发生这种情况。