标记错误：java.util.regex.PatternSyntaxException，悬空元字符“*”
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Tokenizing Error: java.util.regex.PatternSyntaxException, dangling metacharacter '*'
提问by andandandand
I am using split()to tokenize a String separated with *following this format:
我正在使用以下格式split()对字符串进行标记化*：
name*lastName*ID*school*age
%
name*lastName*ID*school*age
%
name*lastName*ID*school*age
I'm reading this from a file named "entrada.al" using this code:
我正在使用以下代码从名为“entrada.al”的文件中读取此内容：
static void leer() {
try {
String ruta="entrada.al";
File myFile = new File (ruta);
FileReader fileReader = new FileReader(myFile);
BufferedReader reader = new BufferedReader(fileReader);
String line = null;
while ((line=reader.readLine())!=null){
if (!(line.equals("%"))){
String [] separado = line.split("*"); //SPLIT CALL
names.add(separado[0]);
lastNames.add(separado[1]);
ids.add(separado[2]);
ages.add(separado[3]);
}
}
reader.close();
}
And I'm getting this exception:
我得到这个例外：
Exception in thread "main" java.util.regex.PatternSyntaxException: Dangling meta character '*' near index 0 *
线程“main”中的异常 java.util.regex.PatternSyntaxException：索引 0 附近的悬空元字符“*”*
My guess is that the lack of a *after age on the original text file is causing this. How do I get around it?
我的猜测是*原始文本文件中缺少after age 导致了这种情况。我该如何解决？
采纳答案by Michael Myers
No, the problem is that *is a reserved character in regexes, so you need to escape it.
不，问题在于它*是正则表达式中的保留字符，因此您需要对其进行转义。
String [] separado = line.split("\*");
*means "zero or more of the previous expression" (see the PatternJavadocs), and you weren't giving it any previous expression, making your split expression illegal. This is why the error was a PatternSyntaxException.
*表示“前一个表达式的零个或多个”（请参阅PatternJavadocs），并且您没有为其提供任何前一个表达式，从而使您的拆分表达式非法。这就是为什么错误是一个PatternSyntaxException.
回答by jdc0589
The first answer covers it.
第一个答案涵盖了它。
Im guessing that somewhere down the line you may decide to store your info in a different class/structure. In that case you probably wouldn't want the results going in to an array from the split() method.
我猜你可能会决定将你的信息存储在不同的类/结构中。在这种情况下，您可能不希望结果从 split() 方法进入数组。
You didn't ask for it, but I'm bored, so here is an example, hope it's helpful.
你没有要求它，但我很无聊，所以这里有一个例子，希望它有帮助。
This might be the class you write to represent a single person:
这可能是您为代表一个人而编写的类：
class Person {
public String firstName;
public String lastName;
public int id;
public int age;
public Person(String firstName, String lastName, int id, int age) {
this.firstName = firstName;
this.lastName = lastName;
this.id = id;
this.age = age;
}
// Add 'get' and 'set' method if you want to make the attributes private rather than public.
}
Then, the version of the parsing code you originally posted would look something like this: (This stores them in a LinkedList, you could use something else like a Hashtable, etc..)
然后，您最初发布的解析代码的版本将如下所示：（这将它们存储在 LinkedList 中，您可以使用其他内容，例如 Hashtable 等。）
try
{
String ruta="entrada.al";
BufferedReader reader = new BufferedReader(new FileReader(ruta));
LinkedList<Person> list = new LinkedList<Person>();
String line = null;
while ((line=reader.readLine())!=null)
{
if (!(line.equals("%")))
{
StringTokenizer st = new StringTokenizer(line, "*");
if (st.countTokens() == 4)
list.add(new Person(st.nextToken(), st.nextToken(), Integer.parseInt(st.nextToken()), Integer.parseInt(st.nextToken)));
else
// whatever you want to do to account for an invalid entry
// in your file. (not 4 '*' delimiters on a line). Or you
// could write the 'if' clause differently to account for it
}
}
reader.close();
}
回答by Vishal Joshi
It is because * is used as a metacharacter to signify one or more occurences of previous character. So if i write M* then it will look for files MMMMMM..... ! Here you are using * as the only character so the compiler is looking for the character to find multiple occurences of,so it throws the exception.:)
这是因为 * 用作元字符来表示前一个字符的一个或多个出现。所以如果我写 M* 那么它会寻找文件 MMMMMM ..... ！在这里，您使用 * 作为唯一的字符，因此编译器正在查找该字符以查找多次出现的字符，因此它会引发异常。:)
回答by Aniket Thakur
I had similar problem with regex = "?". It happens for all special characters that have some meaning in a regex. So you need to have "\\"as a prefix to your regex.
我有类似的问题regex = "?"。它发生在所有在正则表达式中具有某种意义的特殊字符上。因此，您需要将其"\\"作为正则表达式的前缀。
String [] separado = line.split("\*");
