数据解析、文本处理与正则表达式的应用

# 数据解析、文本处理与正则表达式的应用 ## 1. 逗号分隔数据的解析 ### 1.1 问题描述 在处理数据时，我们常常会遇到包含逗号分隔值（CSV）的字符串或文件。许多基于 Windows 的电子表格和一些数据库会使用 CSV 格式来导出数据。我们的任务就是读取这些 CSV 数据。 ### 1.2 解决方案 可以使用自定义的 CSV 类或正则表达式来完成这个任务。 ### 1.3 Java 程序实现 #### 1.3.1 CSVSimple 类示例 ```java import java.util.*; /* Simple demo of CSV parser class. */ public class CSVSimple { public static void main(String[] args) { CSV parser = new CSV( ); List list = parser.parse( "\"LU\",86.25,\"11/4/1998\",\"2:19PM\",+4.0625"); Iterator it = list.iterator( ); while (it.hasNext( )) { System.out.println(it.next( )); } } } ``` 运行这个程序，输出结果如下： ```plaintext > java CSVSimple LU 86.25 11/4/1998 2:19PM +4.0625 > ``` #### 1.3.2 CSV 类实现 ```java import java.util.*; import com.darwinsys.util.Debug; /** Parse comma-separated values (CSV), a common Windows file format. * Sample input: "LU",86.25,"11/4/1998","2:19PM",+4.0625 * <p> * Inner logic adapted from a C++ original that was * Copyright (C) 1999 Lucent Technologies * Excerpted from 'The Practice of Programming' * by Brian W. Kernighan and Rob Pike. * <p> * Included by permission of the http://tpop.awl.com/ web site, * which says: * "You may use this code for any purpose, as long as you leave * the copyright notice and book citation attached." I have done so. * @author Brian W. Kernighan and Rob Pike (C++ original) * @author Ian F. Darwin (translation into Java and removal of I/O) * @author Ben Ballard (rewrote advQuoted to handle '""' and for readability) */ public class CSV { public static final char DEFAULT_SEP = ','; /** Construct a CSV parser, with the default separator (','). */ public CSV( ) { this(DEFAULT_SEP); } /** Construct a CSV parser with a given separator. * @param sep The single char for the separator (not a list of * separator characters) */ public CSV(char sep) { fieldSep = sep; } /** The fields in the current String */ protected List list = new ArrayList( ); /** the separator char for this parser */ protected char fieldSep; /** parse: break the input String into fields * @return java.util.Iterator containing each field * from the original as a String, in order. */ public List parse(String line) { StringBuffer sb = new StringBuffer( ); list.clear( ); // recycle to initial state int i = 0; if (line.length( ) == 0) { list.add(line); return list; } do { sb.setLength(0); if (i < line.length( ) && line.charAt(i) == '"') i = advQuoted(line, sb, ++i); // skip quote else i = advPlain(line, sb, i); list.add(sb.toString( )); Debug.println("csv", sb.toString( )); i++; } while (i < line.length( )); return list; } /** advQuoted: quoted field; return index of next separator */ protected int advQuoted(String s, StringBuffer sb, int i) { int j; int len= s.length( ); for (j=i; j<len; j++) { if (s.charAt(j) == '"' && j+1 < len) { if (s.charAt(j+1) == '"') { j++; // skip escape char } else if (s.charAt(j+1) == fieldSep) { //next delimiter j++; // skip end quotes break; } } else if (s.charAt(j) == '"' && j+1 == len) { // end quotes at end of line break; //done } sb.append(s.charAt(j)); // regular character. } return j; } /** advPlain: unquoted field; return index of next separator */ protected int advPlain(String s, StringBuffer sb, int i) { int j; j = s.indexOf(fieldSep, i); // look for separator Debug.println("csv", "i = " + i + ", j = " + j); if (j == -1) { // none found sb.append(s.substring(i)); return s.length( ); } else { sb.append(s.substring(i, j)); return j; } } } ``` ### 1.4 正则表达式实现 ```java import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.util.ArrayList; import java.util.List; import java.util.regex.Matcher; import java.util.regex.Pattern; /* Simple demo of CSV matching using Regular Expressions. * Does NOT use the "CSV" class defined in the Java CookBook, but uses * a regex pattern simplified from Chapter 7 of <em>Mastering Regular * Expressions</em> (p. 205, first edn.) * @version $Id: ch03,v 1.3 2004/05/04 18:03:14 ian Exp $ */ public class CSVRE { /** The rather involved pattern used to match CSV's consists of three * alternations: the first matches aquoted field, the second unquoted, * the third a null field. */ public static final String CSV_PATTERN = "\"([^\"]+?)\",?|([^,]+),?|,"; private static Pattern csvRE; public static void main(String[] argv) throws IOException { System.out.println(CSV_PATTERN); new CSVRE().process(new BufferedReader(new InputStreamReader(System.in))); } /** Construct a regex-based CSV parser. */ public CSVRE() { csvRE = Pattern.compile(CSV_PATTERN); } /** Process one file. Delegates to parse() a line at a time */ public void process(BufferedReader in) throws IOException { String line; // For each line... while ((line = in.readLine()) != null) { System.out.println("line = `" ```