我原本是C语言背景，虽然已经五年没有使用这种语言了。现在我尝试在Java中从字符串中解析一些值。在C语言中，我会使用sscanf, 但在Java中人们告诉我“使用Scanner或StringTokenizer”，但我不知道如何使用它们来达到我的目的。
我的输入字符串看起来像是 "17-MAR-11 15.52.25.000000000"。在C语言中，我会做这样的事情：
sscanf(thestring, "%d-%s-%d %d.%d.%d.%d", day, month, year, hour, min, sec, fracpart);
但在Java中，我只能做像这样的事情：
scanner.nextInt();
这样做并不允许我检查该模式，而对于“MAR”，我最终不得不执行诸如以下操作：
str.substring(3,6);
很糟糕！肯定有更好的方法吧？
问题在于Java没有像C或C#那样的输出参数（或按引用传递）。
但有一种更好的方法（也更可靠）。使用正则表达式：
Pattern p = Pattern.compile("(\\d+)-(\\p{Alpha}+)-(\\d+) (\\d+)\\.(\\d+)\\.(\\d+)\\.(\\d+)")
Matcher m = p.matcher("17-MAR-11 15.52.25.000000000");
day = m.group(1);
month= m.group(2);
....
当然，C代码更加简洁，但这种技术有一个好处：模式比“%s”和“%d”更精确地指定格式。因此，您可以使用\d{2}来指定日期必须由正好两个数字组成。
m.group() 之前，我认为你需要先调用 m.find()。 - xuhdevm.find()（如上面 xuhdev 所提到的），或者直接使用 if (m.matches()) {m.group(1); ...}。 - Mitrakov Artem以下是使用扫描器（Scanner）的解决方案：
Scanner scanner = new Scanner("17-MAR-11 15.52.25.000000000");
Scanner dayScanner = new Scanner(scanner.next());
Scanner timeScanner = new Scanner(scanner.next());
dayScanner.useDelimiter("-");
System.out.println("day=" + dayScanner.nextInt());
System.out.println("month=" + dayScanner.next());
System.out.println("year=" + dayScanner.nextInt());
timeScanner.useDelimiter("\\.");
System.out.println("hour=" + timeScanner.nextInt());
System.out.println("min=" + timeScanner.nextInt());
System.out.println("sec=" + timeScanner.nextInt());
System.out.println("fracpart=" + timeScanner.nextInt());
这些例子都不令我满意，因此我自己编写了一个Java sscanf实用程序：
https://github.com/driedler/java-sscanf/tree/master/src/util/sscanf
这是解析十六进制字符串的示例：
String buffer = "my hex string: DEADBEEF\n"
Object output[] = Sscanf.scan(buffer, "my hex string: %X\n", 1);
System.out.println("parse count: " + output.length);
System.out.println("hex str1: " + (Long)output[0]);
// Output:
// parse count: 1
// hex str1: 3735928559
SimpleDateFormat format = new SimpleDateFormat("dd-MMM-yy HH.mm.ss.SSS");
try
{
Date parsed = format.parse(dateString);
System.out.println(parsed.toString());
}
catch (ParseException pe)
{
System.out.println("ERROR: Cannot parse \"" + dateString + "\"");
}
public static void stringStuffThing(){
String x = "17-MAR-11 15.52.25.000000000";
String y[] = x.split(" ");
for(String s : y){
System.out.println(s);
}
String date[] = y[0].split("-");
String values[] = y[1].split("\\.");
for(String s : date){
System.out.println(s);
}
for(String s : values){
System.out.println(s);
}
2019年的答案：Java的Scanner可以灵活地读取各种格式。但是，如果您的格式只包含简单的{%d, %f, %s}字段，则可以使用这个小类（约90行）轻松扫描。
import java.util.ArrayList;
/**
* Basic C-style string formatting and scanning.
* The format strings can contain %d, %f and %s codes.
* @author Adam Gawne-Cain
*/
public class CFormat {
private static boolean accept(char t, char c, int i) {
if (t == 'd')
return "0123456789".indexOf(c) >= 0 || i == 0 && c == '-';
else if (t == 'f')
return "-0123456789.+Ee".indexOf(c) >= 0;
else if (t == 's')
return Character.isLetterOrDigit(c);
throw new RuntimeException("Unknown format code: " + t);
}
/**
* Returns string formatted like C, or throws exception if anything wrong.
* @param fmt format specification
* @param args values to format
* @return string formatted like C.
*/
public static String printf(String fmt, Object... args) {
int a = 0;
StringBuilder sb = new StringBuilder();
int n = fmt.length();
for (int i = 0; i < n; i++) {
char c = fmt.charAt(i);
if (c == '%') {
char t = fmt.charAt(++i);
if (t == 'd')
sb.append(((Number) args[a++]).intValue());
else if (t == 'f')
sb.append(((Number) args[a++]).doubleValue());
else if (t == 's')
sb.append(args[a++]);
else if (t == '%')
sb.append(t);
else
throw new RuntimeException("Unknown format code: " + t);
} else
sb.append(c);
}
return sb.toString();
}
/**
* Returns scanned values, or throws exception if anything wrong.
* @param fmt format specification
* @param str string to scan
* @return scanned values
*/
public static Object[] scanf(String fmt, String str) {
ArrayList ans = new ArrayList();
int s = 0;
int ns = str.length();
int n = fmt.length();
for (int i = 0; i < n; i++) {
char c = fmt.charAt(i);
if (c == '%') {
char t = fmt.charAt(++i);
if (t=='%')
c=t;
else {
int s0 = s;
while ((s == s0 || s < ns) && accept(t, str.charAt(s), s - s0))
s++;
String sub = str.substring(s0, s);
if (t == 'd')
ans.add(Integer.parseInt(sub));
else if (t == 'f')
ans.add(Double.parseDouble(sub));
else
ans.add(sub);
continue;
}
}
if (str.charAt(s++) != c)
throw new RuntimeException();
}
if (s < ns)
throw new RuntimeException("Unmatched characters at end of string");
return ans.toArray();
}
}
// Example of "CFormat.scanf"
String str = "17-MAR-11 15.52.25.000000000";
Object[] a = CFormat.scanf("%d-%s-%d %d.%d.%f", str);
// Pick out scanned fields
int day = (Integer) a[0];
String month = (String) a[1];
int year = (Integer) a[2];
int hour = (Integer) a[3];
int min = (Integer) a[4];
double sec = (Double) a[5];
// Example of "CFormat.printf"
System.out.println(CFormat.printf("Got day=%d month=%s hour=%d min=%d sec=%f\n", day, month, year, hour, min, sec));
Matcher matcher = Pattern.match(yourString);
matcher.find();
然后使用Matcher提供的方法来操作你找到的字符串或者不操作。
public static ArrayList<Object> scan(String s, String fmt)
{ ArrayList<Object> result = new ArrayList<Object>();
Scanner scanner = new Scanner(s);
int ind = 0; // s upto ind has been consumed
for (int i = 0; i < fmt.length(); i++)
{ char c = fmt.charAt(i);
if (c == '%' && i < fmt.length() - 1)
{ char d = fmt.charAt(i+1);
if (d == 's')
{ scanner = new Scanner(s.substring(ind));
try {
String v = scanner.next();
ind = ind + v.length();
result.add(v);
}
catch (Exception _ex) {
_ex.printStackTrace();
}
i++;
}
else if (d == 'f')
{ String fchars = "";
for (int j = ind; j < s.length(); j++)
{ char x = s.charAt(j);
if (x == '.' || Character.isDigit(x))
{ fchars = fchars + x; }
else
{ break; }
}
try {
double v = Double.parseDouble(fchars);
ind = ind + (v + "").length();
result.add(v);
}
catch (Exception _ex) {
_ex.printStackTrace();
}
i++;
}
else if (d == 'd')
{ String inchars = "";
for (int j = ind; j < s.length(); j++)
{ char x = s.charAt(j);
if (Character.isDigit(x))
{ inchars = inchars + x; }
else
{ break; }
}
try {
int v = Integer.parseInt(inchars);
ind = ind + (v + "").length();
result.add(v);
}
catch (Exception _ex) {
_ex.printStackTrace();
}
i++;
}
}
else if (s.charAt(ind) == c)
{ ind++; }
else
{ return result; }
}
return result;
}
public static void main(String[] args)
{ ArrayList res = StringLib.scan("100##3.3::20\n", "%d##%f::%d\n");
System.out.println(res);
}
System.in.read() 是另一个选项。
strptime等效的选项，而不是scanf。 - riffraff