使用String.split()将带引号的csv文件拆分为文本分隔符

Question

我有一个逗号分隔文件,其中许多行类似于下面的一行.

Sachin,,M,"Maths,Science,English",Need to improve in these subjects.

引号用于转义用于表示多个值的分隔符逗号.

现在如何使用String.split()if来分割逗号分隔符上的上述值？

Answer 1

public static void main(String[] args) {
    String s = "Sachin,,M,\"Maths,Science,English\",Need to improve in these subjects.";
    String[] splitted = s.split(",(?=([^\"]*\"[^\"]*\")*[^\"]*$)");
    System.out.println(Arrays.toString(splitted));
}

输出:

[Sachin, , M, "Maths,Science,English", Need to improve in these subjects.]

Answer 2

由于您的问题/要求并不是那么复杂,因此可以使用自定义方法,其执行速度提高20倍以上并产生相同的结果.这是基于数据大小和解析行数的变量,对于使用正则表达式的更复杂问题是必须的.

import java.util.Arrays;
import java.util.ArrayList;
public class SplitTest {

public static void main(String[] args) {

    String s = "Sachin,,M,\"Maths,Science,English\",Need to improve in these subjects.";
    String[] splitted = null;

 //Measure Regular Expression
    long startTime = System.nanoTime();
    for(int i=0; i<10; i++)
    splitted = s.split(",(?=([^\"]*\"[^\"]*\")*[^\"]*$)");
    long endTime =   System.nanoTime();

    System.out.println("Took: " + (endTime-startTime));
    System.out.println(Arrays.toString(splitted));
    System.out.println("");


    ArrayList<String> sw = null;        
 //Measure Custom Method
            startTime = System.nanoTime();
    for(int i=0; i<10; i++)
    sw = customSplitSpecific(s);
    endTime =   System.nanoTime();

    System.out.println("Took: " + (endTime-startTime));
    System.out.println(sw);         
}

public static ArrayList<String> customSplitSpecific(String s)
{
    ArrayList<String> words = new ArrayList<String>();
    boolean notInsideComma = true;
    int start =0, end=0;
    for(int i=0; i<s.length()-1; i++)
    {
        if(s.charAt(i)==',' && notInsideComma)
        {
            words.add(s.substring(start,i));
            start = i+1;                
        }   
        else if(s.charAt(i)=='"')
        notInsideComma=!notInsideComma;
    }
    words.add(s.substring(start));
    return words;
}   

}

在我自己的电脑上,这会产生:

Took: 6651100
[Sachin, , M, "Maths,Science,English", Need to improve in these subjects.]

Took: 224179
[Sachin, , M, "Maths,Science,English", Need to improve in these subjects.]

Answer 3

如果您的字符串都是格式良好的,则可以使用以下正则表达式:

String[] res = str.split(",(?=([^\"]|\"[^\"]*\")*$)");

该表达式确保仅在逗号处发生拆分,该逗号后跟偶数(或零)引号(因此不在此类引号内).

然而,使用简单的非正则表达式解析器可能更容易.