JavaでCSVファイルを読み込んで解析する方法

JavaでCSVファイルを読み取って解析する方法

country-csv-example

コンマ区切り値（CSV）ファイルは、通常のプレーンテキストファイルであり、列ごとにデータを格納し、区切り記号で分割します（通常はコンマ「、」です）。

例えば：

1,US,United States
2,MY,Malaysia
3,AU,Australia

"1","US","United States"
"2","MY","Malaysia"
"3","AU","Australia"

Note
コンマ区切り値（CSV）形式については、このRFC4180ドキュメントをお読みください。

CSVファイルには、通常2つの問題があります。

1. セパレータを含むフィールド、たとえばセパレータはコンマであり、コンマを含むフィールドは次のとおりです。

"aaa","b,bb","ccc"

2. 二重引用符はフィールドを囲むために使用され、フィールドは二重引用符を含みます。これを解決するには、フィールド内に表示される二重引用符を、その前に別の二重引用符（RFC4180）を付けてエスケープする必要があります。

"aaa","b""bb","ccc"

このチュートリアルでは、CSVファイルから値を読み取り、解析し、印刷する3つの例を示します。

シンプルなフォーマットのCSVファイルを解析するシンプルなソリューション。
奇妙な形式のCSVファイル（区切り文字または二重引用符を含むフィールド）を解析するための高度なソリューション
サードパーティのソリューション、OpenCSVの例。

1. 簡単な解決策

CSVファイルに「区切り文字または二重引用符」が含まれていないことが確実な場合は、標準のsplit()を使用してCSVファイルを解析します。

1.1 Review a simple CSV file

/Users/example/csv/country.csv

"1.0.0.0","1.0.0.255","16777216","16777471","AU","Australia"
"1.0.1.0","1.0.3.255","16777472","16778239","CN","China"
"1.0.4.0","1.0.7.255","16778240","16779263","AU","Australia"
"1.0.8.0","1.0.15.255","16779264","16781311","CN","China"
"1.0.16.0","1.0.31.255","16781312","16785407","JP","Japan"
"1.0.32.0","1.0.63.255","16785408","16793599","CN","China"
"1.0.64.0","1.0.127.255","16793600","16809983","JP","Japan"
"1.0.128.0","1.0.255.255","16809984","16842751","TH","Thailand"

1.2 No magic, just read above text file, and splits it by a comma separator.

CSVReader.csv

package com.example.csv;

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

public class CSVReader {

    public static void main(String[] args) {

        String csvFile = "/Users/example/csv/country.csv";
        BufferedReader br = null;
        String line = "";
        String cvsSplitBy = ",";

        try {

            br = new BufferedReader(new FileReader(csvFile));
            while ((line = br.readLine()) != null) {

                // use comma as separator
                String[] country = line.split(cvsSplitBy);

                System.out.println("Country [code= " + country[4] + " , name=" + country[5] + "]");

            }

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (br != null) {
                try {
                    br.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }

}

1.3 For JDK 7 and above, uses try-resources.

CSVReader.csv

package com.example.csv;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class CSVReader {

    public static void main(String[] args) {

        String csvFile = "/Users/example/csv/country.csv";
        String line = "";
        String cvsSplitBy = ",";

        try (BufferedReader br = new BufferedReader(new FileReader(csvFile))) {

            while ((line = br.readLine()) != null) {

                // use comma as separator
                String[] country = line.split(cvsSplitBy);

                System.out.println("Country [code= " + country[4] + " , name=" + country[5] + "]");

            }

        } catch (IOException e) {
            e.printStackTrace();
        }

    }

}

出力

Country [code= "AU" , name="Australia"]
Country [code= "CN" , name="China"]
Country [code= "AU" , name="Australia"]
Country [code= "CN" , name="China"]
Country [code= "JP" , name="Japan"]
Country [code= "CN" , name="China"]
Country [code= "JP" , name="Japan"]
Country [code= "TH" , name="Thailand"]

2. アドバンスソリューション

このソリューションは、「セパレーターまたは二重引用符」の問題を含むフィールドを解決し、カスタムセパレーターとカスタム囲まれたフィールドもサポートします。次のCSV解析の例とJUnitテストケースを確認して、その仕組みを理解してください。

Note
繰り返しますが、フィールド内に表示される二重引用符をエスケープする必要がある場合は、たとえば、フィールドの前に別の二重引用符を付けます。

"aaa","b""bb","ccc"

2.1 Review another CSV file

/Users/example/csv/country2.csv

10,AU,Australia
11,AU,Aus""tralia
"12","AU","Australia"
"13","AU","Aus""tralia"
"14","AU","Aus,tralia"

2.2 The below example is inspired by this article – “https://agiletribe.wordpress.com/2012/11/23/the-only-class-you-need-for-csv-files/[Only Class You Need for CSV Files]” (with some fixed to support other features, read “fixed comments”) and also this third party OpenCSV library.

CSVUtils.java

package com.example.utils;

import java.io.File;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class CSVUtils {

    private static final char DEFAULT_SEPARATOR = ',';
    private static final char DEFAULT_QUOTE = '"';

    public static void main(String[] args) throws Exception {

        String csvFile = "/Users/example/csv/country2.csv";

        Scanner scanner = new Scanner(new File(csvFile));
        while (scanner.hasNext()) {
            List line = parseLine(scanner.nextLine());
            System.out.println("Country [id= " + line.get(0) + ", code= " + line.get(1) + " , name=" + line.get(2) + "]");
        }
        scanner.close();

    }

    public static List parseLine(String cvsLine) {
        return parseLine(cvsLine, DEFAULT_SEPARATOR, DEFAULT_QUOTE);
    }

    public static List parseLine(String cvsLine, char separators) {
        return parseLine(cvsLine, separators, DEFAULT_QUOTE);
    }

    public static List parseLine(String cvsLine, char separators, char customQuote) {

        List result = new ArrayList<>();

        //if empty, return!
        if (cvsLine == null && cvsLine.isEmpty()) {
            return result;
        }

        if (customQuote == ' ') {
            customQuote = DEFAULT_QUOTE;
        }

        if (separators == ' ') {
            separators = DEFAULT_SEPARATOR;
        }

        StringBuffer curVal = new StringBuffer();
        boolean inQuotes = false;
        boolean startCollectChar = false;
        boolean doubleQuotesInColumn = false;

        char[] chars = cvsLine.toCharArray();

        for (char ch : chars) {

            if (inQuotes) {
                startCollectChar = true;
                if (ch == customQuote) {
                    inQuotes = false;
                    doubleQuotesInColumn = false;
                } else {

                    //Fixed : allow "" in custom quote enclosed
                    if (ch == '\"') {
                        if (!doubleQuotesInColumn) {
                            curVal.append(ch);
                            doubleQuotesInColumn = true;
                        }
                    } else {
                        curVal.append(ch);
                    }

                }
            } else {
                if (ch == customQuote) {

                    inQuotes = true;

                    //Fixed : allow "" in empty quote enclosed
                    if (chars[0] != '"' && customQuote == '\"') {
                        curVal.append('"');
                    }

                    //double quotes in column will hit this!
                    if (startCollectChar) {
                        curVal.append('"');
                    }

                } else if (ch == separators) {

                    result.add(curVal.toString());

                    curVal = new StringBuffer();
                    startCollectChar = false;

                } else if (ch == '\r') {
                    //ignore LF characters
                    continue;
                } else if (ch == '\n') {
                    //the end, break!
                    break;
                } else {
                    curVal.append(ch);
                }
            }

        }

        result.add(curVal.toString());

        return result;
    }

}

出力

Country [id= 10, code= AU , name=Australia]
Country [id= 11, code= AU , name=Aus"tralia]
Country [id= 12, code= AU , name=Australia]
Country [id= 13, code= AU , name=Aus"tralia]
Country [id= 14, code= AU , name=Aus,tralia]

3.3 Review the following unit test, it test the “commas and double quotes” issue.

CSVUtilsTest.java

package com.example.csv;

import com.example.utils.CSVUtils;
import org.hamcrest.core.IsNull;
import org.junit.Test;

import java.util.List;

import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.core.Is.is;

public class CSVUtilsTest {

    @Test
    public void test_no_quote() {

        String line = "10,AU,Australia";
        List result = CSVUtils.parseLine(line);

        assertThat(result, IsNull.notNullValue());
        assertThat(result.size(), is(3));
        assertThat(result.get(0), is("10"));
        assertThat(result.get(1), is("AU"));
        assertThat(result.get(2), is("Australia"));

    }

    @Test
    public void test_no_quote_but_double_quotes_in_column() throws Exception {

        String line = "10,AU,Aus\"\"tralia";

        List result = CSVUtils.parseLine(line);
        assertThat(result, IsNull.notNullValue());
        assertThat(result.size(), is(3));
        assertThat(result.get(0), is("10"));
        assertThat(result.get(1), is("AU"));
        assertThat(result.get(2), is("Aus\"tralia"));

    }

    @Test
    public void test_double_quotes() {

        String line = "\"10\",\"AU\",\"Australia\"";
        List result = CSVUtils.parseLine(line);

        assertThat(result, IsNull.notNullValue());
        assertThat(result.size(), is(3));
        assertThat(result.get(0), is("10"));
        assertThat(result.get(1), is("AU"));
        assertThat(result.get(2), is("Australia"));

    }

    @Test
    public void test_double_quotes_but_double_quotes_in_column() {

        String line = "\"10\",\"AU\",\"Aus\"\"tralia\"";
        List result = CSVUtils.parseLine(line);

        assertThat(result, IsNull.notNullValue());
        assertThat(result.size(), is(3));
        assertThat(result.get(0), is("10"));
        assertThat(result.get(1), is("AU"));
        assertThat(result.get(2), is("Aus\"tralia"));

    }

    @Test
    public void test_double_quotes_but_comma_in_column() {

        String line = "\"10\",\"AU\",\"Aus,tralia\"";
        List result = CSVUtils.parseLine(line);

        assertThat(result, IsNull.notNullValue());
        assertThat(result.size(), is(3));
        assertThat(result.get(0), is("10"));
        assertThat(result.get(1), is("AU"));
        assertThat(result.get(2), is("Aus,tralia"));

    }

}

3.4 Review another unit test, it test the custom separator and custom enclosed field.

CSVUtilsTestCustom.java

package com.example.csv;

import com.example.utils.CSVUtils;
import org.hamcrest.core.IsNull;
import org.junit.Test;

import java.util.List;

import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.core.Is.is;

public class CSVUtilsTestCustom {

    @Test
    public void test_custom_separator() {

        String line = "10|AU|Australia";
        List result = CSVUtils.parseLine(line, '|');

        assertThat(result, IsNull.notNullValue());
        assertThat(result.size(), is(3));
        assertThat(result.get(0), is("10"));
        assertThat(result.get(1), is("AU"));
        assertThat(result.get(2), is("Australia"));

    }

    @Test
    public void test_custom_separator_and_quote() {

        String line = "'10'|'AU'|'Australia'";
        List result = CSVUtils.parseLine(line, '|', '\'');

        assertThat(result, IsNull.notNullValue());
        assertThat(result.size(), is(3));
        assertThat(result.get(0), is("10"));
        assertThat(result.get(1), is("AU"));
        assertThat(result.get(2), is("Australia"));

    }

    @Test
    public void test_custom_separator_and_quote_but_custom_quote_in_column() {

        String line = "'10'|'AU'|'Aus|tralia'";
        List result = CSVUtils.parseLine(line, '|', '\'');

        assertThat(result, IsNull.notNullValue());
        assertThat(result.size(), is(3));
        assertThat(result.get(0), is("10"));
        assertThat(result.get(1), is("AU"));
        assertThat(result.get(2), is("Aus|tralia"));

    }

    @Test
    public void test_custom_separator_and_quote_but_double_quotes_in_column() {

        String line = "'10'|'AU'|'Aus\"\"tralia'";
        List result = CSVUtils.parseLine(line, '|', '\'');

        assertThat(result, IsNull.notNullValue());
        assertThat(result.size(), is(3));
        assertThat(result.get(0), is("10"));
        assertThat(result.get(1), is("AU"));
        assertThat(result.get(2), is("Aus\"tralia"));

    }

}

3. OpenCSVの例

上記の単純で高度なソリューションに慣れていない場合は、サードパーティのCSVライブラリ–OpenCSVを使用してみてください。

3.1 Maven.

pom.xml

    
        com.opencsv
        opencsv
        3.8

3.2 Review a CSV file.

/Users/example/csv/country3.csv

10,AU,Australia
11,AU,Aus""tralia
"12","AU","Australia"
"13","AU","Aus""tralia"
"14","AU","Aus,tralia"

3.2 OpenCSV example to parse above CSV file.

CSVReaderExample.java

package com.example.csv;

import com.opencsv.CSVReader;

import java.io.FileReader;
import java.io.IOException;

public class CSVReaderExample {

    public static void main(String[] args) {

        String csvFile = "/Users/example/csv/country3.csv";

        CSVReader reader = null;
        try {
            reader = new CSVReader(new FileReader(csvFile));
            String[] line;
            while ((line = reader.readNext()) != null) {
                System.out.println("Country [id= " + line[0] + ", code= " + line[1] + " , name=" + line[2] + "]");
            }
        } catch (IOException e) {
            e.printStackTrace();
        }


    }

}

出力

Country [id= 10, code= AU , name=Australia]
Country [id= 11, code= AU , name=Aus"tralia]
Country [id= 12, code= AU , name=Australia]
Country [id= 13, code= AU , name=Aus"tralia]
Country [id= 14, code= AU , name=Aus,tralia]

Note
その他の例については、このOpenCSV official documentationを参照してください。

完了しました。

TOC

JavaでCSVファイルを読み込んで解析する方法

JavaでCSVファイルを読み取って解析する方法

1. 簡単な解決策

2. アドバンスソリューション

3. OpenCSVの例

参考文献

Related