Question

我想从多列csv文件中读取特定列，并使用Java在其他csv文件中打印这些列。有什么帮助吗？以下是我的代码逐行打印每个标记..但我打算只打印多列csv中的几列。

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.util.StringTokenizer;

public class ParseCSV {

    public static void main(String[] args) {

        try
        {

            //csv file containing data
            String strFile = "C:\\Users\\rsaluja\\CMS_Evaluation\\Drupal_12_08_27.csv";

            //create BufferedReader to read csv file
            BufferedReader br = new BufferedReader( new FileReader(strFile));
            String strLine = "";
            StringTokenizer st = null;
            int lineNumber = 0, tokenNumber = 0;

            //read comma separated file line by line
            while( (strLine = br.readLine()) != null)
            {
                lineNumber++;

                //break comma separated line using ","
                st = new StringTokenizer(strLine, ",");

                while(st.hasMoreTokens())
                {
                //display csv values
                tokenNumber++;
                System.out.println("Line # " + lineNumber +
                                ", Token # " + tokenNumber
                                + ", Token : "+ st.nextToken());


                            System.out.println(cols[4]);

Answer 1

您应该使用优秀的OpenCSV来读取和写入CSV文件。为了使您的示例适应使用库，它将如下所示：

public class ParseCSV {
  public static void main(String[] args) {
    try {
      //csv file containing data
      String strFile = "C:/Users/rsaluja/CMS_Evaluation/Drupal_12_08_27.csv";
      CSVReader reader = new CSVReader(new FileReader(strFile));
      String [] nextLine;
      int lineNumber = 0;
      while ((nextLine = reader.readNext()) != null) {
        lineNumber++;
        System.out.println("Line # " + lineNumber);

        // nextLine[] is an array of values from the line
        System.out.println(nextLine[4] + "etc...");
      }
    }
  }
}

Answer 2

以非常简单读取CSV文件，并在Java中使用。您实际上不要求加载任何额外第三方库来为您执行此操作。 CSV（逗号分隔值）文件只是普通的纯文本文件，逐列存储数据，并用分隔符（例如逗号＆＃34;，＆＃34;）拆分。

为了从CSV文件中读取特定列，有几种方法。最简单的如下：

在没有任何第三方库的情况下读取CSV的代码

BufferedReader br = new BufferedReader(new FileReader(csvFile));
while ((line = br.readLine()) != null) {
    // use comma as separator
    String[] cols = line.split(cvsSplitBy);
    System.out.println("Coulmn 4= " + cols[4] + " , Column 5=" + cols[5]);
}

如果您注意到，此处不执行任何特殊。它只是读取文本文件，并通过分隔符吐出 - ＆＃34;，＆＃34;。

考虑GeoLite Free Downloadable Databases

中遗留国家/地区CSV数据的摘录

"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"

以上代码将输出如下：

Column 4= "AU" , Column 5="Australia"
Column 4= "CN" , Column 5="China"
Column 4= "AU" , Column 5="Australia"
Column 4= "CN" , Column 5="China"
Column 4= "JP" , Column 5="Japan"
Column 4= "CN" , Column 5="China"
Column 4= "JP" , Column 5="Japan"
Column 4= "TH" , Column 5="Thailand"

事实上，您可以put Map中的列，然后只需使用key即可获取值。

Shishir

Answer 3

对不起，但这些答案都没有提供最佳解决方案。如果您使用OpenCSV等库，则必须编写大量代码来处理特殊情况以从特定列中提取信息。

例如，如果列的列数少于您所使用的行数，则必须编写大量代码来处理它。使用OpenCSV示例：

  CSVReader reader = new CSVReader(new FileReader(strFile));
  String [] nextLine;
  while ((nextLine = reader.readNext()) != null) {
       //let's say you are interested in getting columns 20, 30, and 40
       String[] outputRow = new String[3];
       if(parsedRow.length < 40){
            outputRow[2] = null;
       } else {
            outputRow[2] = parsedRow[40]
       }
       if(parsedRow.length < 30){
            outputRow[1] = null;
       } else {
            outputRow[1] = parsedRow[30]
       }
       if(parsedRow.length < 20){
            outputRow[0] = null;
       } else {
            outputRow[0] = parsedRow[20]
       }

  }

这是一个简单要求的代码。如果您尝试按名称获取列的值，情况会变得更糟。您应该使用更现代的解析器，例如uniVocity-parsers提供的解析器。

要可靠，轻松地获取所需的列，只需写下：

CsvParserSettings settings = new CsvParserSettings();
parserSettings.selectIndexes(20, 30, 40);
CsvParser parser = new CsvParser(settings);
List<String[]> allRows = parser.parseAll(new FileReader(yourFile));

披露：我是这个图书馆的作者。它是开源和免费的（Apache V2.0许可证）。

Answer 4

我建议使用Apache Commons CSV https://commons.apache.org/proper/commons-csv/

以下是一个例子：

    Path currentRelativePath = Paths.get("");
    String currentPath = currentRelativePath.toAbsolutePath().toString();
    String csvFile = currentPath + "/pathInYourProject/test.csv";

    Reader in;
    Iterable<CSVRecord> records = null;
    try
    {
        in = new FileReader(csvFile);
        records = CSVFormat.EXCEL.withHeader().parse(in); // header will be ignored
    }
    catch (IOException e)
    {
        e.printStackTrace();
    }

    for (CSVRecord record : records) {
        String line = "";
        for ( int i=0; i < record.size(); i++)
        {
            if ( line == "" )
                line = line.concat(record.get(i));
            else
                line = line.concat("," + record.get(i));
        }
        System.out.println("read line: " + line);
    }

它会自动识别，和＆＃34; ，但不能; （也许可以配置......）。

我的示例文件是：

col1,col2,col3
val1,"val2",val3
"val4",val5
val6;val7;"val8"

输出是：

read line: val1,val2,val3
read line: val4,val5
read line: val6;val7;"val8"

最后一行被视为一个值。

Answer 5

阅读一些特定的专栏我做了这样的事情：

dpkcs.csv content:
FN,LN,EMAIL,CC
Name1,Lname1,email1@gmail.com,CC1
Nmae2,Lname2,email2r@gmail.com,CC2

阅读它的功能：

private void getEMailRecepientList() {
                List<EmailRecepientData> emailList = null;// Blank list of POJO class
                Scanner scanner = null;
                BufferedReader reader = null;
                try {
                    reader = new BufferedReader(new FileReader("dpkcs.csv"));
                    Map<String, Integer> mailHeader = new HashMap<String, Integer>();
                    // read file line by line
                    String line = null;
                    int index = 0;
                    line = reader.readLine();
                    // Get header from 1st row of csv
                    if (line != null) {
                        StringTokenizer str = new StringTokenizer(line, ",");
                        int headerCount = str.countTokens();
                        for (int i = 0; i < headerCount; i++) {
                            String headerKey = str.nextToken();
                            mailHeader.put(headerKey.toUpperCase(), new Integer(i));

                        }
                    }
                    emailList = new ArrayList<EmailRecepientData>();

                    while ((line = reader.readLine()) != null) {
                    // POJO class for getter and setters
                        EmailRecepientData email = new EmailRecepientData();
                        scanner = new Scanner(line);
                        scanner.useDelimiter(",");
                    //Use Specific key to get value what u want
                        while (scanner.hasNext()) {
                            String data = scanner.next();
                            if (index == mailHeader.get("EMAIL"))
                                email.setEmailId(data);
                            else if (index == mailHeader.get("FN"))
                                email.setFirstName(data);
                            else if (index == mailHeader.get("LN"))
                                email.setLastName(data);
                            else if (index == mailHeader.get("CC"))
                                email.setCouponCode(data);

                            index++;
                        }
                        index = 0;
                        emailList.add(email);
                    }
                    reader.close();
                } catch (Exception e) {
                    StringWriter stack = new StringWriter();
                    e.printStackTrace(new PrintWriter(stack));

                } finally {
                    scanner.close();
                }

                System.out.println("list--" + emailList);

            }

POJO班级：

public class EmailRecepientData {
    private String emailId;
    private String firstName;
    private String lastName;
    private String couponCode;

    public String getEmailId() {
        return emailId;
    }

    public void setEmailId(String emailId) {
        this.emailId = emailId;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getCouponCode() {
        return couponCode;
    }

    public void setCouponCode(String couponCode) {
        this.couponCode = couponCode;
    }

    @Override
    public String toString() {
        return "Email Id=" + emailId + ", First Name=" + firstName + " ,"
                + " Last Name=" + lastName + ", Coupon Code=" + couponCode + "";
    }

}

Answer 6

我们可以单独使用核心java东西来逐列读取CVS文件。这是我为我的要求编写的示例代码。我相信这会对某些人有所帮助。

 BufferedReader br = new BufferedReader(new FileReader(csvFile));
    String line = EMPTY;
    int lineNumber = 0;

    int productURIIndex = -1;
    int marketURIIndex = -1;
    int ingredientURIIndex = -1;
    int companyURIIndex = -1;

    // read comma separated file line by line
    while ((line = br.readLine()) != null) {
        lineNumber++;
        // use comma as line separator
        String[] splitStr = line.split(COMMA);
        int splittedStringLen = splitStr.length;

        // get the product title and uri column index by reading csv header
        // line
        if (lineNumber == 1) {
            for (int i = 0; i < splittedStringLen; i++) {
                if (splitStr[i].equals(PRODUCTURI_TITLE)) {
                    productURIIndex = i;
                    System.out.println("product_uri index:" + productURIIndex);
                }

                if (splitStr[i].equals(MARKETURI_TITLE)) {
                    marketURIIndex = i;
                    System.out.println("marketURIIndex:" + marketURIIndex);
                }

                if (splitStr[i].equals(COMPANYURI_TITLE)) {
                    companyURIIndex = i;
                    System.out.println("companyURIIndex:" + companyURIIndex);
                }

                if (splitStr[i].equals(INGREDIENTURI_TITLE)) {
                    ingredientURIIndex = i;
                    System.out.println("ingredientURIIndex:" + ingredientURIIndex);
                }
            }
        } else {
            if (splitStr != null) {
                String conditionString = EMPTY;
                // avoiding arrayindexoutboundexception when the line
                // contains only ,,,,,,,,,,,,,
                for (String s : splitStr) {
                    conditionString = s;
                }
                if (!conditionString.equals(EMPTY)) {
                    if (productURIIndex != -1) {
                        productCVSUriList.add(splitStr[productURIIndex]);
                    }
                    if (companyURIIndex != -1) {
                        companyCVSUriList.add(splitStr[companyURIIndex]);
                    }
                    if (marketURIIndex != -1) {
                        marketCVSUriList.add(splitStr[marketURIIndex]);
                    }
                    if (ingredientURIIndex != -1) {
                        ingredientCVSUriList.add(splitStr[ingredientURIIndex]);
                    }
                }
            }
        }

Answer 7

嗯，这个怎么样!!

此代码计算csv文件中的行数和列数。试试吧!!

    static int[] getRowsColsNo() {
    Scanner scanIn = null;
    int rows = 0;
    int cols = 0;
    String InputLine = "";
    try {
        scanIn = new Scanner(new BufferedReader(
                new FileReader("filename.csv")));
        scanIn.useDelimiter(",");
        while (scanIn.hasNextLine()) {
            InputLine = scanIn.nextLine();
            String[] InArray = InputLine.split(",");
            rows++;
            cols = InArray.length;
        }

    } catch (Exception e) {
        System.out.println(e);
    }
    return new int[] { rows, cols };
}

逐列读取CSV文件

7 个答案: