Java 字符转义

Question

在编程时，我发现 java 字符串有奇怪的行为。我正在尝试将字符串解析为带有参数的命令：

下面是调试过程中变量的截图。

这是我读取命令的代码：

public List<String> readCommand(Sender sender, String command) {
    boolean isInQuote = false;
    List<String> splits = new ArrayList();
    String current = "";
    char[] arr = command.toCharArray();
    for (int i = 0; i < command.toCharArray().length; i++) {
        char c = arr[i];
        if (c == '"') {
        isInQuote = !isInQuote;

        if (!isInQuote) {
            splits.add(current);
            current = "";
        }
        }

        if (isInQuote) {
        current += c;
        } else {
        if (c == ' ' || i == arr.length - 1) {
            if (i == arr.length - 1) {
            current += c;
            }
            splits.add(current);
            current = "";
        } else {
            current += c;
        }
        }
    }

    return splits;
    }

正如测试中预期的那样；该字符串应解析为：

"this"
"is a test"
"now"

而是解析为：

"this"
"\"is a test"
"\""
"now"

为什么转义引号不起作用，我做错了什么？

P.S.: 我会尝试研究这个主题，但我不知道如何称呼它。正在用引号解析参数...?

更新：在你的帮助下，我发现了另一个我修复的错误。该代码现在可以正常工作。现在剩下的就是重新制作它:)。 \" 不工作真的让我很困惑。http://pastebin.com/AdBUqJvH

Answer 1

这是您任务的解决方案。

public static void main(String[] args) {
    List<String> splits = readCommand("this \"is a\" test\" now");
    for(String str : splits) {
            System.out.println("_"+str+"_");
    }
}

public static List<String> readCommand(String command) {
    List<String> list = Arrays.asList(command.split("\""));
    List<String> list2 = new ArrayList<>();
    for(String str : list) {
        str = checkFirst(str);
        str = checkLast(str);
        list2.add(str);
    }
    return list2;
}

private static String checkFirst(String str) {
    if (str.charAt(0) == ' ') {
        str = checkFirst(str.substring(1));
    }
    return str;
}

private static String checkLast(String str) {
    if (str.charAt(str.length() - 1) == ' ') {
        str = checkLast(str.substring(0, str.length() - 1));
    }
    return str;
}

Answer 2

你的代码对我来说工作得很好。除了输出是

这个"is a test"“现在

而不是

这个 "is a test" 现在

我为此做了一个小改动

你说你不知道输入并不总是包含'"'，但是你用'"'硬编码它，所以[Igor Sadovnikov]的答案可能更好？

    public static void main(String[] args) {
        String s = "this \"is a test\" now";
        List<String> commands = readCommand(null, s);
        for (String command : commands) {
            System.out.print(command + " ");
        }
    }

    private static List<String> readCommand(Object sender, String command) {
        boolean isInQuote = false;
        List<String> splits = new ArrayList<String>();
        String current = "";
        char[] arr = command.toCharArray();
        for (int i = 0; i < command.toCharArray().length; i++) {
            char c = arr[i];
            if (c == '"') {
                isInQuote = !isInQuote;

                if (!isInQuote) {
                    //CHANGE HERE  ... added + c
                    splits.add(current + c);
                    current = "";
                }
            }

            if (isInQuote) {
                current += c;
            } else {
                if (c == ' ' || i == arr.length - 1) {
                    if (i == arr.length - 1) {
                        current += c;
                    }
                    splits.add(current);
                    current = "";
                } 
                // --- CHANGE HERE
                else if (c != '"') {
                    current += c;
                }
            }
        }

        return splits;
    }

Answer 3

首先让我们简化您当前的尝试：

public static void main(String[] args) throws Exception {
    String data = "this \"is a test\" now \"hello\" goodbye";

    List<String> splits = new ArrayList();
    String current = "";
    boolean inQuote = false;        
    for (int i = 0; i < data.length(); i++) {
        if (data.charAt(i) == ' ' && !inQuote) {
            // Add your current split word and move on to the next character
            splits.add(current);
            current = "";
            continue; 
        } else if (data.charAt(i) == '\"') {
            // Flip the flag whenever you run across a quotation mark
            inQuote = !inQuote;
        }

        // Add current character to string, spaces never get added
        current += data.charAt(i);
    }
    // Add remaining split data from hitting the end of data
    if (!current.isEmpty()) {
        splits.add(current);
    }

    // Display results
    for (String split : splits) {
        System.out.println(split);
    }
}

结果：

this
"is a test"
now
"hello"
goodbye

正则表达式

然后您可以使用 Regex 缩短您的代码，如下所示（结果相同）：

public static void main(String[] args) throws Exception {
    String data = "this \"is a test\" now \"hello\" goodbye";

    Matcher matcher = Pattern.compile("[^\s\"']+|\"[^\"]*\"|'[^']*'").matcher(data);
    while (matcher.find()) {
        System.out.println(matcher.group());
    }
}

Java 字符转义

Java character escaping

java

escaping

正则表达式