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https://issues.apache.org/jira/browse/KAFKA-7326?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16599673#comment-16599673
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ASF GitHub Bot commented on KAFKA-7326:
---------------------------------------
guozhangwang closed pull request #5579: KAFKA-7326: KStream.print() should
flush on each line for PrintStream
URL: https://github.com/apache/kafka/pull/5579
This is a PR merged from a forked repository.
As GitHub hides the original diff on merge, it is displayed below for
the sake of provenance:
As this is a foreign pull request (from a fork), the diff is supplied
below (as it won't show otherwise due to GitHub magic):
diff --git a/docs/streams/developer-guide/dsl-api.html
b/docs/streams/developer-guide/dsl-api.html
index beb83a3970a..da1b78dafcb 100644
--- a/docs/streams/developer-guide/dsl-api.html
+++ b/docs/streams/developer-guide/dsl-api.html
@@ -631,6 +631,7 @@ <h2><a class="toc-backref" href="#id7">Overview</a><a
class="headerlink" href="#
caveats.
(<a class="reference external"
href="../../../javadoc/org/apache/kafka/streams/kstream/KStream.html#print--">details</a>)</p>
<p>Calling <code class="docutils literal"><span
class="pre">print()</span></code> is the same as calling <code class="docutils
literal"><span class="pre">foreach((key,</span> <span class="pre">value)</span>
<span class="pre">-></span> <span class="pre">System.out.println(key</span>
<span class="pre">+</span> <span class="pre">",</span> <span
class="pre">"</span> <span class="pre">+</span> <span
class="pre">value))</span></code></p>
+ <p><code class="docutils literal"><span
class="pre">print</span></code> is mainly for debugging/testing purposes, and
it will try to flush on each record print. Hence it <strong>should not</strong>
be used for production usage if performance requirements are concerned.</p>
<div class="last highlight-java"><div
class="highlight"><pre><span></span><span class="n">KStream</span><span
class="o"><</span><span class="kt">byte</span><span class="o">[],</span>
<span class="n">String</span><span class="o">></span> <span
class="n">stream</span> <span class="o">=</span> <span class="o">...;</span>
<span class="c1">// print to sysout</span>
<span class="n">stream</span><span class="o">.</span><span
class="na">print</span><span class="o">();</span>
diff --git
a/streams/src/main/java/org/apache/kafka/streams/kstream/KStream.java
b/streams/src/main/java/org/apache/kafka/streams/kstream/KStream.java
index ae3b28a35ce..cf2ce75450e 100644
--- a/streams/src/main/java/org/apache/kafka/streams/kstream/KStream.java
+++ b/streams/src/main/java/org/apache/kafka/streams/kstream/KStream.java
@@ -359,6 +359,9 @@
/**
* Print the records of this KStream using the options provided by {@link
Printed}
+ * Note that this is mainly for debugging/testing purposes, and it will
try to flush on each record print.
+ * It <em>SHOULD NOT</em> be used for production usage if performance
requirements are concerned.
+ *
* @param printed options for printing
*/
void print(final Printed<K, V> printed);
diff --git
a/streams/src/main/java/org/apache/kafka/streams/kstream/internals/PrintForeachAction.java
b/streams/src/main/java/org/apache/kafka/streams/kstream/internals/PrintForeachAction.java
index 174319fec4b..861dfd3b84e 100644
---
a/streams/src/main/java/org/apache/kafka/streams/kstream/internals/PrintForeachAction.java
+++
b/streams/src/main/java/org/apache/kafka/streams/kstream/internals/PrintForeachAction.java
@@ -51,6 +51,9 @@
public void apply(final K key, final V value) {
final String data = String.format("[%s]: %s", label, mapper.apply(key,
value));
printWriter.println(data);
+ if (!closable) {
+ printWriter.flush();
+ }
}
public void close() {
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> Let KStream.print() to flush on each printed line
> -------------------------------------------------
>
> Key: KAFKA-7326
> URL: https://issues.apache.org/jira/browse/KAFKA-7326
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Affects Versions: 2.0.0
> Reporter: Guozhang Wang
> Assignee: huxihx
> Priority: Major
> Labels: newbie++
>
> Today, {{KStream.print()}} is implemented as a special "foreach" function as
> below:
> {code}
> @Override
> public void apply(final K key, final V value) {
> final String data = String.format("[%s]: %s", label,
> mapper.apply(key, value));
> printWriter.println(data);
> }
> {code}
> Note that since {{this.printWriter = new PrintWriter(new
> OutputStreamWriter(outputStream, StandardCharsets.UTF_8));}}, without
> flushing the writer we do not guarantee that printed lines are written to the
> underlying `outputStream` in time.
> Since {{KStream.print()}} is mainly for debugging / testing / demoing
> purposes, not for performance, I think it is okay to enforce auto flushing.
> This would include:
> 1. set {{autoFlush}} in the constructor of printWriter.
> 2. document in java-docs of {{KStream.print}} that this is for debug /
> testing purposes only, and it will try to flush on each record print, and
> hence should not be used for production usage if performance requirement is
> key.
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