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8031650: Update bulk operation demo 

Reviewed-by: psandoz, mduigou
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src/share/sample/lambda/BulkDataOperations/index.html 0 → 100644
浏览文件 @ 303aa45f
<!DOCTYPE html>
<html>
<head>
<title>Bulk Data Operations Demo</title>
</head>
<body>
<h2>Bulk Data Operations Demo</h2>
<p>
This demo shows how to use bulk data operations with the new JDK8
Collections API.
The demo also demonstrates new features of JDK8 such as lambda expressions
and method/constructor references.
</p>
<ul>
<li><h3>CSV Processor</h3>
<p>
Analyzes a CSV file, finds and collects useful information, computes
different statistics. For more information, see the source file.
</p>
Source: <a href="src/CSVProcessor.java">src/CSVProcessor.java</a>
<li><h3>Grep</h3>
<p>
Behaves like the standard Linux tool Grep. For more information, see
the source file.
</p>
Source: <a href="src/Grep.java">src/Grep.java</a>
<li><h3>PasswordGenerator</h3>
<p>
Produces a password of desired length. For more information see
source file.
</p>
Source: <a
href="src/PasswordGenerator.java">src/PasswordGenerator.java</a>
<li><h3>WC</h3>
<p>
Counts newlines, words, characters, and the maximum line length of a
text file. For more information, see the source
file.
</p>
Source: <a href="src/WC.java">src/WC.java</a>
</ul>
</body>
</html>
\ No newline at end of file
src/share/sample/lambda/BulkDataOperations/src/CSVProcessor.java 0 → 100644
浏览文件 @ 303aa45f
/*
* Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* - Neither the name of Oracle nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/*
* This source code is provided to illustrate the usage of a given feature
* or technique and has been deliberately simplified. Additional steps
* required for a production-quality application, such as security checks,
* input validation, and proper error handling, might not be present in
* this sample code.
*/
import java.io.BufferedReader;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.*;
import java.util.function.*;
import java.util.regex.Pattern;
import java.util.stream.Collector;
import java.util.stream.Collectors;
import static java.lang.Double.parseDouble;
import static java.util.stream.Collectors.*;
/**
* CSVProcessor is a tool for processing CSV files. There are several
* command-line options. Consult the {@link #printUsageAndExit} method for
* instructions and command line parameters. This sample shows examples of the
* following features:
* <ul>
* <li>Lambda and bulk operations. Working with streams: map(...), filter(...),
* sorted(...) methods. The collect(...) method with different collectors:
* Collectors.maxBy(...), Collectors.minBy(...), Collectors.toList(),
* Collectors.toCollection(...), Collectors.groupingBy(...),
* Collectors.toDoubleSummaryStatistics(...), and a custom Collector.</li>
* <li>Static method reference for printing values.</li>
* <li>Try-with-resources feature for closing files.</li>
* <li>Switch by String feature.</li>
* <li>Other new APIs: Pattern.asPredicate(), BinaryOperator
* BufferedReader.lines(), Collection.forEach(...), Comparator.comparing(...),
* Comparator.reversed(), Arrays.stream(...).</li>
* </ul>
*
*/
public class CSVProcessor {
//Number of characters that may be read
private static final int READ_AHEAD_LIMIT = 100_000_000;
/**
* The main method for the CSVProcessor program. Run the program with an
* empty argument list to see possible arguments.
*
* @param args the argument list for CSVProcessor.
*/
public static void main(String[] args) {
if (args.length < 2) {
printUsageAndExit();
}
try (BufferedReader br = new BufferedReader(
Files.newBufferedReader(Paths.get(args[args.length - 1])))) {
//Assume that the first line contains column names.
List<String> header = Arrays.stream(br.readLine().split(","))
.map(String::trim).collect(toList());
//Calculate an index of the column in question.
int column = getColumnNumber(header, args[1]);
switch (args[0]) {
case "sort":
verifyArgumentNumber(args, 4);
//Define the sort order.
boolean isAsc;
switch (args[2].toUpperCase()) {
case "ASC":
isAsc = true;
break;
case "DESC":
isAsc = false;
break;
default:
printUsageAndExit("Illegal argument" + args[2]);
return;//Should not be reached.
}
/*
* Create a comparator that compares lines by comparing
* values in the specified column.
*/
Comparator<String> cmp
= Comparator.comparing(str -> getCell(str, column),
String.CASE_INSENSITIVE_ORDER);
/*
* sorted(...) is used to sort records.
* forEach(...) is used to output sorted records.
*/
br.lines().sorted(isAsc ? cmp : cmp.reversed())
.forEach(System.out::println);
break;
case "search":
verifyArgumentNumber(args, 4);
/*
* Records are filtered by a regex.
* forEach(...) is used to output filtered records.
*/
Predicate<String> pattern
= Pattern.compile(args[2]).asPredicate();
br.lines().filter(str -> pattern.test(getCell(str, column)))
.forEach(System.out::println);
break;
case "groupby":
verifyArgumentNumber(args, 3);
/*
* Group lines by values in the column with collect(...), and
* print with forEach(...) for every distinct value within
* the column.
*/
br.lines().collect(
Collectors.groupingBy(str -> getCell(str, column),
toCollection(TreeSet::new)))
.forEach((str, set) -> {
System.out.println(str + ":");
set.forEach(System.out::println);
});
break;
case "stat":
verifyArgumentNumber(args, 3);
/*
* BufferedReader will be read several times.
* Mark this point to return here after each pass.
* BufferedReader will be read right after the headers line
* because it is already read.
*/
br.mark(READ_AHEAD_LIMIT);
/*
* Statistics can be collected by a custom collector in one
* pass. One pass is preferable.
*/
System.out.println(
br.lines().collect(new Statistics(column)));
/*
* Alternatively, statistics can be collected
* by a built-in API in several passes.
* This method demonstrates how separate operations can be
* implemented using a built-in API.
*/
br.reset();
statInSeveralPasses(br, column);
break;
default:
printUsageAndExit("Illegal argument" + args[0]);
}
} catch (IOException e) {
printUsageAndExit(e.toString());
}
}
private static void statInSeveralPasses(BufferedReader br, int column)
throws IOException {
System.out.println("#-----Statistics in several passes-------#");
//Create a comparator to compare records by the column.
Comparator<String> comparator
= Comparator.comparing(
(String str) -> parseDouble(getCell(str, column)));
//Find max record by using Collectors.maxBy(...)
System.out.println(
"Max: " + br.lines().collect(maxBy(comparator)).get());
br.reset();
//Find min record by using Collectors.minBy(...)
System.out.println(
"Min: " + br.lines().collect(minBy(comparator)).get());
br.reset();
//Compute the average value and sum with
//Collectors.toDoubleSummaryStatistics(...)
DoubleSummaryStatistics doubleSummaryStatistics
= br.lines().collect(summarizingDouble(
str -> parseDouble(getCell(str, column))));
System.out.println("Average: " + doubleSummaryStatistics.getAverage());
System.out.println("Sum: " + doubleSummaryStatistics.getSum());
}
private static void verifyArgumentNumber(String[] args, int n) {
if (args.length != n) {
printUsageAndExit("Expected " + n + " arguments but was "
+ args.length);
}
}
private static int getColumnNumber(List<String> header, String name) {
int column = header.indexOf(name);
if (column == -1) {
printUsageAndExit("There is no column with name " + name);
}
return column;
}
private static String getCell(String record, int column) {
return record.split(",")[column].trim();
}
private static void printUsageAndExit(String... str) {
System.out.println("Usages:");
System.out.println("CSVProcessor sort COLUMN_NAME ASC|DESC FILE");
System.out.println("Sort lines by column COLUMN_NAME in CSV FILE\n");
System.out.println("CSVProcessor search COLUMN_NAME REGEX FILE");
System.out.println("Search for REGEX in column COLUMN_NAME in CSV FILE\n");
System.out.println("CSVProcessor groupby COLUMN_NAME FILE");
System.out.println("Split lines into different groups according to column "
+ "COLUMN_NAME value\n");
System.out.println("CSVProcessor stat COLUMN_NAME FILE");
System.out.println("Compute max/min/average/sum statistics by column "
+ "COLUMN_NAME\n");
Arrays.asList(str).forEach(System.err::println);
System.exit(1);
}
/*
* This is a custom implementation of the Collector interface.
* Statistics are objects gather max,min,sum,average statistics.
*/
private static class Statistics
implements Collector<String, Statistics, Statistics> {
/*
* This implementation does not need to be thread safe because
* the parallel implementation of
* {@link java.util.stream.Stream#collect Stream.collect()}
* provides the necessary partitioning and isolation for safe parallel
* execution.
*/
private String maxRecord;
private String minRecord;
private double sum;
private int lineCount;
private final BinaryOperator<String> maxOperator;
private final BinaryOperator<String> minOperator;
private final int column;
public Statistics(int column) {
this.column = column;
Comparator<String> cmp = Comparator.comparing(
(String str) -> parseDouble(getCell(str, column)));
maxOperator = BinaryOperator.maxBy(cmp);
minOperator = BinaryOperator.minBy(cmp);
}
/*
* Process line.
*/
public Statistics accept(String line) {
maxRecord = maxRecord == null
? line : maxOperator.apply(maxRecord, line);
minRecord = minRecord == null
? line : minOperator.apply(minRecord, line);
sum += parseDouble(getCell(line, column));
lineCount++;
return this;
}
/*
* Merge two Statistics.
*/
public Statistics combine(Statistics stat) {
maxRecord = maxOperator.apply(maxRecord, stat.getMaxRecord());
minRecord = minOperator.apply(minRecord, stat.getMinRecord());
sum += stat.getSum();
lineCount += stat.getLineCount();
return this;
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append("#------Statistics------#\n");
sb.append("Max: ").append(getMaxRecord()).append("\n");
sb.append("Min: ").append(getMinRecord()).append("\n");
sb.append("Sum = ").append(getSum()).append("\n");
sb.append("Average = ").append(average()).append("\n");
sb.append("#------Statistics------#\n");
return sb.toString();
}
@Override
public Supplier<Statistics> supplier() {
return () -> new Statistics(column);
}
@Override
public BiConsumer<Statistics, String> accumulator() {
return Statistics::accept;
}
@Override
public BinaryOperator<Statistics> combiner() {
return Statistics::combine;
}
@Override
public Function<Statistics, Statistics> finisher() {
return stat -> stat;
}
@Override
public Set<Characteristics> characteristics() {
return EnumSet.of(Characteristics.IDENTITY_FINISH);
}
private String getMaxRecord() {
return maxRecord;
}
private String getMinRecord() {
return minRecord;
}
private double getSum() {
return sum;
}
private double average() {
return sum / lineCount;
}
private int getLineCount() {
return lineCount;
}
}
}
src/share/sample/lambda/BulkDataOperations/src/Grep.java 0 → 100644
浏览文件 @ 303aa45f
/*
* Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* - Neither the name of Oracle nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/*
* This source code is provided to illustrate the usage of a given feature
* or technique and has been deliberately simplified. Additional steps
* required for a production-quality application, such as security checks,
* input validation, and proper error handling, might not be present in
* this sample code.
*/
import java.io.IOException;
import java.io.UncheckedIOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.Arrays;
import java.util.List;
import java.util.regex.Pattern;
import java.util.stream.Stream;
import static java.util.stream.Collectors.toList;
/**
* Grep prints lines matching a regex. See {@link #printUsageAndExit(String...)}
* method for instructions and command line parameters. This sample shows
* examples of using next features:
* <ul>
* <li>Lambda and bulk operations. Working with streams:
* map(...),filter(...),flatMap(...),limit(...) methods.</li>
* <li>Static method reference for printing values.</li>
* <li>New Collections API forEach(...) method.</li>
* <li>Try-with-resources feature.</li>
* <li>new Files.walk(...), Files.lines(...) API.</li>
* <li>Streams that need to be closed.</li>
* </ul>
*
*/
public class Grep {
private static void printUsageAndExit(String... str) {
System.out.println("Usage: " + Grep.class.getSimpleName()
+ " [OPTION]... PATTERN FILE...");
System.out.println("Search for PATTERN in each FILE. "
+ "If FILE is a directory then whole file tree of the directory"
+ " will be processed.");
System.out.println("Example: grep -m 100 'hello world' menu.h main.c");
System.out.println("Options:");
System.out.println(" -m NUM: stop analysis after NUM matches");
Arrays.asList(str).forEach(System.err::println);
System.exit(1);
}
/**
* The main method for the Grep program. Run program with empty argument
* list to see possible arguments.
*
* @param args the argument list for Grep.
* @throws java.io.IOException If an I/O error occurs.
*/
public static void main(String[] args) throws IOException {
long maxCount = Long.MAX_VALUE;
if (args.length < 2) {
printUsageAndExit();
}
int i = 0;
//parse OPTIONS
while (args[i].startsWith("-")) {
switch (args[i]) {
case "-m":
try {
maxCount = Long.parseLong(args[++i]);
} catch (NumberFormatException ex) {
printUsageAndExit(ex.toString());
}
break;
default:
printUsageAndExit("Unexpected option " + args[i]);
}
i++;
}
//parse PATTERN
Pattern pattern = Pattern.compile(args[i++]);
if (i == args.length) {
printUsageAndExit("There are no files for input");
}
try {
/*
* First obtain the list of all paths.
* For a small number of arguments there is little to be gained
* by producing this list in parallel. For one argument
* there will be no parallelism.
*
* File names are converted to paths. If a path is a directory then
* Stream is populated with whole file tree of the directory by
* flatMap() method. Files are filtered from directories.
*/
List<Path> files = Arrays.stream(args, i, args.length)
.map(Paths::get)
// flatMap will ensure each I/O-based stream will be closed
.flatMap(Grep::getPathStream)
.filter(Files::isRegularFile)
.collect(toList());
/*
* Then operate on that list in parallel.
* This is likely to give a more even distribution of work for
* parallel execution.
*
* Lines are extracted from files. Lines are filtered by pattern.
* Stream is limited by number of matches. Each remaining string is
* displayed in std output by method reference System.out::println.
*/
files.parallelStream()
// flatMap will ensure each I/O-based stream will be closed
.flatMap(Grep::path2Lines)
.filter(pattern.asPredicate())
.limit(maxCount)
.forEachOrdered(System.out::println);
} catch (UncheckedIOException ioe) {
printUsageAndExit(ioe.toString());
}
}
/**
* Flattens file system hierarchy into a stream. This code is not inlined
* for the reason of Files.walk() throwing a checked IOException that must
* be caught.
*
* @param path - the file or directory
* @return Whole file tree starting from path, a stream with one element -
* the path itself - if it is a file.
*/
private static Stream<Path> getPathStream(Path path) {
try {
return Files.walk(path);
} catch (IOException e) {
throw new UncheckedIOException(e);
}
}
/**
* Produces a stream of lines from a file. The result is a stream in order
* to close it later. This code is not inlined for the reason of
* Files.lines() throwing a checked IOException that must be caught.
*
* @param path - the file to read
* @return stream of lines from the file
*/
private static Stream<String> path2Lines(Path path) {
try {
return Files.lines(path);
} catch (IOException e) {
throw new UncheckedIOException(e);
}
}
}
src/share/sample/lambda/BulkDataOperations/src/PasswordGenerator.java 0 → 100644
浏览文件 @ 303aa45f
/*
* Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* - Neither the name of Oracle nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/*
* This source code is provided to illustrate the usage of a given feature
* or technique and has been deliberately simplified. Additional steps
* required for a production-quality application, such as security checks,
* input validation, and proper error handling, might not be present in
* this sample code.
*/
import java.security.SecureRandom;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.IntStream;
/**
* Generates password of desired length. See {@link #usage} method
* for instructions and command line parameters. This sample shows usages of:
* <ul>
* <li>Method references.</li>
* <li>Lambda and bulk operations. A stream of random integers is mapped to
* chars, limited by desired length and printed in standard output as password
* string.</li>
* </ul>
*
*/
public class PasswordGenerator {
private static void usage() {
System.out.println("Usage: PasswordGenerator LENGTH");
System.out.println(
"Password Generator produces password of desired LENGTH.");
}
private static final List<Integer> PASSWORD_CHARS = new ArrayList<>();
//Valid symbols.
static {
IntStream.rangeClosed('0', '9').forEach(PASSWORD_CHARS::add); // 0-9
IntStream.rangeClosed('A', 'Z').forEach(PASSWORD_CHARS::add); // A-Z
IntStream.rangeClosed('a', 'z').forEach(PASSWORD_CHARS::add); // a-z
}
/**
* The main method for the PasswordGenerator program. Run program with empty
* argument list to see possible arguments.
*
* @param args the argument list for PasswordGenerator.
*/
public static void main(String[] args) {
if (args.length != 1) {
usage();
return;
}
long passwordLength;
try {
passwordLength = Long.parseLong(args[0]);
if (passwordLength < 1) {
printMessageAndUsage("Length has to be positive");
return;
}
} catch (NumberFormatException ex) {
printMessageAndUsage("Unexpected number format" + args[0]);
return;
}
/*
* Stream of random integers is created containing Integer values
* in range from 0 to PASSWORD_CHARS.size().
* The stream is limited by passwordLength.
* Valid chars are selected by generated index.
*/
new SecureRandom().ints(passwordLength, 0, PASSWORD_CHARS.size())
.map(PASSWORD_CHARS::get)
.forEach(i -> System.out.print((char) i));
}
private static void printMessageAndUsage(String message) {
System.err.println(message);
usage();
}
}
src/share/sample/lambda/BulkDataOperations/src/WC.java 0 → 100644
浏览文件 @ 303aa45f
/*
* Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* - Neither the name of Oracle nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/*
* This source code is provided to illustrate the usage of a given feature
* or technique and has been deliberately simplified. Additional steps
* required for a production-quality application, such as security checks,
* input validation, and proper error handling, might not be present in
* this sample code.
*/
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.function.Consumer;
import java.util.regex.Pattern;
/**
* WC - Prints newline, word, and character counts for each file. See
* the {@link #usage} method for instructions and command line parameters. This
* sample shows usages of:
* <ul>
* <li>Lambda and bulk operations. Shows how to create a custom collector to
* gather custom statistics. Implements the collection of statistics using a
* built-in API.</li>
* <li>Constructor reference.</li>
* <li>Try-with-resources feature.</li>
* </ul>
*
*/
public class WC {
//The number of characters that may be read.
private static final int READ_AHEAD_LIMIT = 100_000_000;
//The pattern for splitting strings by non word characters to get words.
private static final Pattern nonWordPattern = Pattern.compile("\\W");
/**
* The main method for the WC program. Run the program with an empty
* argument list to see possible arguments.
*
* @param args the argument list for WC
* @throws java.io.IOException If an input exception occurred.
*/
public static void main(String[] args) throws IOException {
if (args.length != 1) {
usage();
return;
}
try (BufferedReader reader = new BufferedReader(
new FileReader(args[0]))) {
reader.mark(READ_AHEAD_LIMIT);
/*
* Statistics can be gathered in four passes using a built-in API.
* The method demonstrates how separate operations can be
* implemented using a built-in API.
*/
collectInFourPasses(reader);
/*
* Usage of several passes to collect data is not the best way.
* Statistics can be gathered by a custom collector in one pass.
*/
reader.reset();
collectInOnePass(reader);
} catch (FileNotFoundException e) {
usage();
System.err.println(e);
}
}
private static void collectInFourPasses(BufferedReader reader)
throws IOException {
/*
* Input is read as a stream of lines by lines().
* Every line is turned into a stream of chars by the flatMapToInt(...)
* method.
* Length of the stream is counted by count().
*/
System.out.println("Character count = "
+ reader.lines().flatMapToInt(String::chars).count());
/*
* Input is read as a stream of lines by lines().
* Every line is split by nonWordPattern into words by flatMap(...)
* method.
* Empty lines are removed by the filter(...) method.
* Length of the stream is counted by count().
*/
reader.reset();
System.out.println("Word count = "
+ reader.lines()
.flatMap(nonWordPattern::splitAsStream)
.filter(str -> !str.isEmpty()).count());
reader.reset();
System.out.println("Newline count = " + reader.lines().count());
/*
* Input is read as a stream of lines by lines().
* Every line is mapped to its length.
* Maximum of the lengths is calculated.
*/
reader.reset();
System.out.println("Max line length = "
+ reader.lines().mapToInt(String::length).max().getAsInt());
}
private static void collectInOnePass(BufferedReader reader) {
/*
* The collect() method has three parameters:
* The first parameter is the {@code WCStatistic} constructor reference.
* collect() will create {@code WCStatistics} instances, where
* statistics will be aggregated.
* The second parameter shows how {@code WCStatistics} will process
* String.
* The third parameter shows how to merge two {@code WCStatistic}
* instances.
*
* Also {@code Collector} can be used, which would be more reusable
* solution. See {@code CSVProcessor} example for how {@code Collector}
* can be implemented.
*
* Note that the any performance increase when going parallel will
* depend on the size of the input (lines) and the cost per-element.
*/
WCStatistics wc = reader.lines().parallel()
.collect(WCStatistics::new,
WCStatistics::accept,
WCStatistics::combine);
System.out.println(wc);
}
private static void usage() {
System.out.println("Usage: " + WC.class.getSimpleName() + " FILE");
System.out.println("Print newline, word,"
+ " character counts and max line length for FILE.");
}
private static class WCStatistics implements Consumer<String> {
/*
* @implNote This implementation does not need to be thread safe because
* the parallel implementation of
* {@link java.util.stream.Stream#collect Stream.collect()}
* provides the necessary partitioning and isolation for safe parallel
* execution.
*/
private long characterCount;
private long lineCount;
private long wordCount;
private long maxLineLength;
/*
* Processes line.
*/
@Override
public void accept(String line) {
characterCount += line.length();
lineCount++;
wordCount += nonWordPattern.splitAsStream(line)
.filter(str -> !str.isEmpty()).count();
maxLineLength = Math.max(maxLineLength, line.length());
}
/*
* Merges two WCStatistics.
*/
public void combine(WCStatistics stat) {
wordCount += stat.wordCount;
lineCount += stat.lineCount;
characterCount += stat.characterCount;
maxLineLength = Math.max(maxLineLength, stat.maxLineLength);
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append("#------WCStatistic------#\n");
sb.append("Character count = ").append(characterCount).append('\n');
sb.append("Word count = ").append(wordCount).append('\n');
sb.append("Newline count = ").append(lineCount).append('\n');
sb.append("Max line length = ").append(maxLineLength).append('\n');
return sb.toString();
}
}
}
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