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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8"/>
<title>Simple Use Case</title>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<body>
<table id="doc-title" cellspacing="0" cellpadding="0">
<tr>
<td align="left" valign="top">
<b>Java Platform, Enterprise Edition (Java EE) 8</b><br />
<b>The Java EE Tutorial</b>
<!-- <p class="beta">Beta Draft (Pre-General Availability)</p> -->
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</table>
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<table width="90%" id="top-nav" cellspacing="0" cellpadding="0">
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<a href="batch-processing002.html">
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</table>
<div class="sect1">
<h2 id="simple-use-case">Simple Use Case</h2>
<div class="sectionbody">
<div class="paragraph">
<p>This section demonstrates how to define a simple job using the Job
Specification Language (JSL) and how to implement the corresponding
batch artifacts. Refer to the rest of the sections in this chapter for
detailed descriptions of the elements in the batch framework.</p>
</div>
<div class="paragraph">
<p>The following job definition specifies a chunk step and a task step as
follows:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-oac_no_warn" data-lang="oac_no_warn"><?xml version="1.0" encoding="UTF-8"?>
<job id="simplejob" xmlns="http://xmlns.jcp.org/xml/ns/javaee"
version="1.0">
<properties>
<property name="input_file" value="input.txt"/>
<property name="output_file" value="output.txt"/>
</properties>
<step id="mychunk" next="mytask">
<chunk>
<reader ref="MyReader"></reader>
<processor ref="MyProcessor"></processor>
<writer ref="MyWriter"></writer>
</chunk>
</step>
<step id="mytask">
<batchlet ref="MyBatchlet"></batchlet>
<end on="COMPLETED"/>
</step>
</job></code></pre>
</div>
</div>
<div class="sect2">
<h3 id="chunk-step">Chunk Step</h3>
<div class="paragraph">
<p>In most cases, you have to implement a checkpoint class for
chunk-oriented steps. The following class just keeps track of the line
number in a text file:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-oac_no_warn" data-lang="oac_no_warn">public class MyCheckpoint implements Serializable {
private long lineNum = 0;
public void increase() { lineNum++; }
public long getLineNum() { return lineNum; }
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>The following item reader implementation continues reading the input
file from the provided checkpoint if the job was restarted. The items
consist of each line in the text file (in more complex scenarios, the
items are custom Java types and the input source can be a database):</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-oac_no_warn" data-lang="oac_no_warn">@Dependent
@Named("MyReader")
public class MyReader implements javax.batch.api.chunk.ItemReader {
private MyCheckpoint checkpoint;
private BufferedReader breader;
@Inject
JobContext jobCtx;
public MyReader() {}
@Override
public void open(Serializable ckpt) throws Exception {
if (ckpt == null)
checkpoint = new MyCheckpoint();
else
checkpoint = (MyCheckpoint) ckpt;
String fileName = jobCtx.getProperties()
.getProperty("input_file");
breader = new BufferedReader(new FileReader(fileName));
for (long i = 0; i < checkpoint.getLineNum(); i++)
breader.readLine();
}
@Override
public void close() throws Exception {
breader.close();
}
@Override
public Object readItem() throws Exception {
String line = breader.readLine();
return line;
}
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>In the following case, the item processor only converts the line to
uppercase. More complex examples can process items in different ways or
transform them into custom output Java types:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-oac_no_warn" data-lang="oac_no_warn">@Dependent
@Named("MyProcessor")
public class MyProcessor implements javax.batch.api.chunk.ItemProcessor {
public MyProcessor() {}
@Override
public Object processItem(Object obj) throws Exception {
String line = (String) obj;
return line.toUpperCase();
}
}</code></pre>
</div>
</div>
<table class="tableblock frame-all grid-all spread">
<colgroup>
<col style="width: 100%;">
</colgroup>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><div><div class="paragraph">
<p>Note:</p>
</div>
<div class="paragraph">
<p>The batch processing API does not support generics. In most cases, you
need to cast items to their specific type before processing them.</p>
</div></div></td>
</tr>
</tbody>
</table>
<div class="paragraph">
<p>The item writer writes the processed items to the output file. It
overwrites the output file if no checkpoint is provided; otherwise, it
resumes writing at the end of the file. Items are written in chunks:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-oac_no_warn" data-lang="oac_no_warn">@Dependent
@Named("MyWriter")
public class MyWriter implements javax.batch.api.chunk.ItemWriter {
private BufferedWriter bwriter;
@Inject
private JobContext jobCtx;
@Override
public void open(Serializable ckpt) throws Exception {
String fileName = jobCtx.getProperties()
.getProperty("output_file");
bwriter = new BufferedWriter(new FileWriter(fileName,
(ckpt != null)));
}
@Override
public void writeItems(List<Object> items) throws Exception {
for (int i = 0; i < items.size(); i++) {
String line = (String) items.get(i);
bwriter.write(line);
bwriter.newLine();
}
}
@Override
public Serializable checkpointInfo() throws Exception {
return new MyCheckpoint();
}</code></pre>
</div>
</div>
</div>
<div class="sect2">
<h3 id="task-step">Task Step</h3>
<div class="paragraph">
<p>The task step displays the length of the output file. In more complex
scenarios, task steps perform any task that does not fit the chunk
processing programming model:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-oac_no_warn" data-lang="oac_no_warn">@Dependent
@Named("MyBatchlet")
public class MyBatchlet implements javax.batch.api.chunk.Batchlet {
@Inject
private JobContext jobCtx;
@Override
public String process() throws Exception {
String fileName = jobCtx.getProperties()
.getProperty("output_file");
System.out.println(""+(new File(fileName)).length());
return "COMPLETED";
}
}</code></pre>
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