java - 用双引号将 CSV 行引起来/创建自定义 main 方法

Question

我必须采用 IBM 创建的 CSVReader 并进行更改以满足我的要求。我是java新手，不知道如何做除了#1之外的任何事情，我的要求是:

1. 通过命令行获取 CSV
2. 添加主方法
3. 每行用双引号引起来
4. 输出新的 CSV

例如。输入乔丹，迈克尔，J，”，23
前任。输出“乔丹，迈克尔，J，”，23“

背景信息:该程序将被添加到 shell 脚本中，正在添加该功能，因为如果输入单个双引号，则 csv 会损坏

这是代码:

package Scripts;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;
import java.util.ArrayList;
import java.util.List;

public class CSVReader 
{
    private BufferedReader br;
    private boolean hasNext = true;
    private static char separator = ' ';
    private static char quotechar = ' '; 

    public static final char DEFAULT_SEPARATOR = ',';
    public static final char DEFAULT_QUOTE_CHARACTER = '"';

    public static void main(final String[] args) throws IOException {
    final String csvFile = args[0];
    final ArrayList<String[]> allElements = new ArrayList<String[]>();
    final CSVReader csvReader = new CSVReader(br, separator, quotechar, csvFile);
    csvTransformer.readAll();
    csvTransformer.close();
}

    public CSVReader(final Reader reader) throws FileNotFoundException {
        this(reader, DEFAULT_SEPARATOR);
    }

    public CSVReader(final Reader reader, final char separator) throws FileNotFoundException {
        this(reader, separator, DEFAULT_QUOTE_CHARACTER, null);
    }
    public CSVReader(final Reader reader, final char separator, final char quotechar, final String csvFile) throws FileNotFoundException {
        CSVTransformer.br = new BufferedReader(new FileReader(csvFile));
        this.separator = separator;
        this.quotechar = quotechar;
    }


/**
 * Reads the entire file into a List with each element being a String[] of tokens.
 * 
 * return a List of String[], with each String[] representing a line of the file.
 */
    public List readAll() throws IOException 
    {
        List allElements = new ArrayList();
        while (hasNext) 
        {
            String[] nextLineAsTokens = readNext();
            if (nextLineAsTokens != null) 
                allElements.add(nextLineAsTokens);
        }
        return allElements;
    }

/**
 * Reads the next line from the buffer and converts to a string array.
 * 
 * return a string array with each comma-separated element as a separate entry.
 */
    public String[] readNext() throws IOException {
        String nextLine = getNextLine();
        return hasNext ? parseLine(nextLine) : null;
    }

/**
 * Reads the next line from the file.
 * 
 * return the next line from the file without trailing newline
 */
    private String getNextLine() throws IOException {
        String nextLine = br.readLine();
        if (nextLine == null) {
            hasNext = false;
        }
        return hasNext ? nextLine : null;
    }

/**
 * Parses an incoming String and returns an array of elements.
 * 
 * @param nextLine
 *            the string to parse
 * @return the comma-tokenized list of elements, or null if nextLine is null
 * @throws IOException if bad things happen during the read
 */
    private String[] parseLine(String nextLine) throws IOException {
        if (nextLine == null) {
            return null;
        }
        List tokensOnThisLine = new ArrayList();
        StringBuffer sb = new StringBuffer();
        boolean inQuotes = false;
        do {
            if (inQuotes) {
            // continuing a quoted section, reappend newline
                sb.append("\n");
                nextLine = getNextLine();
                if (nextLine == null)
                break;
            }
            for (int i = 0; i < nextLine.length(); i++) {
                char c = nextLine.charAt(i);
                if (c == quotechar) {
                // this gets complex... the quote may end a quoted block, or escape another quote.
                // do a 1-char lookahead:
                if(inQuotes)  // we are in quotes, therefore there can be escaped quotes in here.
                        && nextLine.length() > (i+1)  // there is indeed another character to check.
                        && nextLine.charAt(i+1) == quotechar )
                    { // ..and that char. is a quote also.
                    // we have two quote chars in a row == one quote char, so consume them both and
                    // put one on the token. we do *not* exit the quoted text.
                        sb.append(nextLine.charAt(i+1));
                        i++;
                    }
                    else
                    {
                        inQuotes = !inQuotes;
                    }
                }
                else if (c == separator && !inQuotes) {
                    tokensOnThisLine.add(sb.toString());
                    sb = new StringBuffer(); // start work on next token
                }
                else {
                    sb.append(c);
                }
            }
        } while (inQuotes);
        tokensOnThisLine.add(sb.toString());
        return (String[]) tokensOnThisLine.toArray(new String[0]);
    }

    public void close() throws IOException {
        br.close();
    }
}
on

Answer 1

如果您唯一需要的是转义双引号，一个简单的方法就是不将 CSV 文件视为 CSV，而是将其视为简单的文本文件。

首先:Java 中的 main 方法非常简单。使用此声明:

public static void main(String... args){
    //do your stuff
    // args is a String array containing parameters passed to your script, like your file. to get the first param, use args[0] , for the second it's args[1] ...
}

如果在被调用的java类中找到main方法，java将自动使用main方法。

重要的一点:main方法必须是公共(public)静态的并且不返回任何内容正如您在这里看到的:Java spec, chapter 12

根据您的需要，读取文件中的每一行并将其替换为新文件中此函数的结果:

/**
 * 
 * replace quotes in a line and append/prepend quotes to the line and return it
 * 
 */
private static String correctQuotesInLine(String nextLine) {
    if (nextLine == null) {
        return null;
    }

    //replace any single " in line
    String result = nextLine.replaceAll("\"", "\"\"");
    //prepend and append line with quotes
     result = "\"" + result + "\"";


    return result;
}

要写入结果文件，您可以使用这些信息:

how to write files line by line using java