An example of parsing a file with Java8 stream and lambda expressions

Recently I want to extract the specified data from a log file, which is part of the log:

2015-01-06 11:33:03 b.s.d.task [INFO] Emitting:eventtorequestsbolt __ack_ack [-6722594615019711369- 1335723027906100557]22015-01-06 11:33:03 c.s.p.d.packagesprovider [INFO] = = =---> Loaded package com.foo.bar32015-01-06 11:33:04 b.s.d.executor [INFO] processing received message Source:eventtomanagebolt:2, stream: _ _ack_ack, ID: {}, [ -6722594615019711369-1335723027906100557]42015-01-06 11:33:04 C.s.p.d.packagesprovider [INFO] ===- --Loaded Package co.il.boo52015-01-06 11:33:04 c.s.p.d.packagesprovider [INFO] = = =---> Loaded package Dot.org.biz

I'm going to use stream and lambda expressions in Java8 to do this.

Read file

First I want the reading log file and then put each line of the log into a stream.

Stream<string> lines = Files.lines (Paths.get (args[1]));

Filter the related rows

I need to get the package name and write it to another file, not all the rows contain the data I want, so I only filter the related rows.

Lines.filter (Line-line.contains ("= = =---> Loaded package")

Parse related rows

Next, I want to parse the related rows. I split each row of data into a string array and get the last element of the array. In other words, I've been mapping two times. First from a row of data to an array and then from an array to a string.

. Map (line-Line.split ("")). Map (arr. arr[arr.length-1])

Write to output file

The final step is to write each string to the output file. This is the last operation.

. ForEach (Package-WriteToFile (FW, package));

Write ToFile is a way of customizing me. The reason for this is that the Java file system throws IOException, but you cannot use a checked exception in a lambda expression.

The following is the complete code:

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 (out put);//@formatter: Offlines.filter (line-line.contains ("= = =---> Loaded package"). Map, line-Line.split (" "). (arr[arr.length-1). ForEach (Package-WriteToFile (FW, package));//@formatter: Onfw.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);}}}

Original address: http://www.javacodegeeks.com/2015/01/java-8-stream-and-lambda-expressions-parsing-file-example.html

An example of parsing a file with Java8 stream and lambda expressions