Recently I wanted to extract certain data from an output log. Here’s part of the log file:
2015-01-06 11:33:03 b.s.d.task [INFO] Emitting: eVentToRequestsBolt __ack_ack [-6722594615019711369 -1335723027906100557]
2015-01-06 11:33:03 c.s.p.d.PackagesProvider [INFO] ===---> Loaded package com.foo.bar
2015-01-06 11:33:04 b.s.d.executor [INFO] Processing received message source: eventToManageBolt:2, stream: __ack_ack, id: {}, [-6722594615019711369 -1335723027906100557]
2015-01-06 11:33:04 c.s.p.d.PackagesProvider [INFO] ===---> Loaded package co.il.boo
2015-01-06 11:33:04 c.s.p.d.PackagesProvider [INFO] ===---> Loaded package dot.org.bizI decided to do it using the Java8 Stream and Lambda Expression features.
Read the file
First, I needed to read the log file and put the lines in a Stream:
Stream<String> lines = Files.lines(Paths.get(args[1]));
Filter relevant lines
I needed to get the packages names and write them into another file. Not all lines contained the data I need, hence filter only relevant ones.
lines.filter(line -> line.contains("===---> Loaded package"))Parsing the relevant lines
Then, I needed to parse the relevant lines. I did it by first splitting each line to an array of Strings and then taking the last element in that array. In other words, I did a double mapping. First a line to an array and then an array to a String.
.map(line -> line.split(" "))
.map(arr -> arr[arr.length - 1])Writing to output file
The last part was taking each string and write it to a file. That was the terminal operation.
.forEach(package -> writeToFile(fw, package));
writeToFile is a method I created. The reason is that Java File System throws IOException. You can’t use checked exceptions in lambda expressions.
Here’s a full example (note, I don’t check input)
import java.io.FileWriter;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Stream;
public class App {
public static void main(String[] args) throws IOException {
Stream<String> lines = null;
if (args.length == 2) {
lines = Files.lines(Paths.get(args[1]));
} else {
String s1 = "2015-01-06 11:33:03 b.s.d.task [INFO] Emitting: adEventToRequestsBolt __ack_ack [-6722594615019711369 -1335723027906100557]";
String s2 = "2015-01-06 11:33:03 b.s.d.executor [INFO] Processing received message source: eventToManageBolt:2, stream: __ack_ack, id: {}, [-6722594615019711369 -1335723027906100557]";
String s3 = "2015-01-06 11:33:04 c.s.p.d.PackagesProvider [INFO] ===---> Loaded package com.foo.bar";
String s4 = "2015-01-06 11:33:04 c.s.p.d.PackagesProvider [INFO] ===---> Loaded package co.il.boo";
String s5 = "2015-01-06 11:33:04 c.s.p.d.PackagesProvider [INFO] ===---> Loaded package dot.org.biz";
List<String> rows = Arrays.asList(s1, s2, s3, s4, s5);
lines = rows.stream();
}
new App().parse(lines, args[0]);
}
private void parse(Stream<String> lines, String output) throws IOException {
final FileWriter fw = new FileWriter(output);
//@formatter:off
lines.filter(line -> line.contains("===---> Loaded package"))
.map(line -> line.split(" "))
.map(arr -> arr[arr.length - 1])
.forEach(package -> writeToFile(fw, package));
//@formatter:on
fw.close();
lines.close();
}
private void writeToFile(FileWriter fw, String package) {
try {
fw.write(String.format("%s%n", package));
} catch (IOException e) {
throw new RuntimeException(e);
}
}
}| Reference: | Java 8 Stream and Lambda Expressions – Parsing File Example from our JCG partner Eyal Golan at the Learning and Improving as a Craftsman Developer blog. |
