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KAFKA-7326: KStream.print() should flush on each line for PrintStream (#5579) 

Reviewers: Matthias J. Sax <matthias@confluent.io>, Guozhang Wang <guozhang@confluent.io>, Bill Bejeck <bill@confluent.io>, Kamal Chandraprakash <kamal.chandraprakash@gmail.com>
This commit is contained in:
huxi 2018-09-02 00:48:50 +08:00 committed by Guozhang Wang
parent 4f38c8cd60
commit aa7358e8cc
3 changed files with 7 additions and 0 deletions
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1
docs/streams/developer-guide/dsl-api.html
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@ -654,6 +654,7 @@
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">-&gt;</span> <span class="pre">System.out.println(key</span> <span class="pre">+</span> <span class="pre">&quot;,</span> <span class="pre">&quot;</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">&lt;</span><span class="kt">byte</span><span class="o">[],</span> <span class="n">String</span><span class="o">&gt;</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>

3
streams/src/main/java/org/apache/kafka/streams/kstream/KStream.java
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@ -359,6 +359,9 @@ public interface KStream<K, V> {
/**
* 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);

3
streams/src/main/java/org/apache/kafka/streams/kstream/internals/PrintForeachAction.java
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@ -51,6 +51,9 @@ public class PrintForeachAction<K, V> implements ForeachAction<K, V> {
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() {