Java中的转义

羿起小憩 2021-08-30

3656

1. Java中为什么要用转义？

Java中一些特殊字符（如单引号、双引号、换行、反斜杠等），如果不用转义，则无法输出显示。

2. 常用的转义字符

3. 如何做unescape？

有些情况下我们需要忽略转义，比如将某个java方法的输出作为参数传递传去

4. 对双引号和单引号做unescape

  /**
     * 
     * @param text
     * @return
     */
    public static String unEscapeString(String text) {
        StringBuilder unescapeStr = new StringBuilder();
        for ( int i=0; i<text.length(); i++ ) {
            char curChar = text.charAt(i);
            char nextChar = curChar;
            if(i+1 < text.length()) {
                nextChar = text.charAt(i+1);
            }
            if(!(curChar == '\\' &&  (nextChar == '\"' || nextChar == '\''))) {
                unescapeStr.append(curChar);   
            }
        }
        return unescapeStr.toString();
    }

5. 单引号和双引号做转义

public static String escapeString(String str, boolean isDoubleQuote) {
        String escapedStr = str;
        if(isDoubleQuote) {
            escapedStr = str.replace("\\\"", "\"").replace("\"", "\\\"");
        } else {
            escapedStr = str.replace("\\\"", "\"").replace("\\'", "'").replace("'", "\\'");
        }
        if(escapedStr.contains("\n")) {
            escapedStr = escapedStr.replace("\n", "\\n");
        }
        return escapedStr;
    }

6. API

https://commons.apache.org/proper/commons-text/javadocs/api-release/org/apache/commons/text/StringEscapeUtils.html#escapeJava-java.lang.String-

但是在实际使用中，可能是需要部分忽略转义，所以还是需要自定义转义和忽略转义的方法

escapeJava

public static final String escapeJava(String input)

Escapes the characters in a String
using Java String rules.

Deals correctly with quotes and control-chars (tab, backslash, cr, ff, etc.)

So a tab becomes the characters '\\'
and 't'
.

The only difference between Java strings and JavaScript strings is that in JavaScript, a single quote and forward-slash (/) are escaped.

Example:

 input string: He didn't say, "Stop!"
 output string: He didn't say, \"Stop!\"

Parameters:
input
- String to escape values in, may be null
Returns:
String with escaped values, null
if null string input

unescapeJava
public static final String unescapeJava(String input)
Unescapes any Java literals found in the String
. For example, it will turn a sequence of '\'
and 'n'
into a newline character, unless the '\'
is preceded by another '\'
.

Parameters:
input
- the String
to unescape, may be null
Returns:
a new unescaped String
, null
if null string input

java

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Java中的转义

escapeJava

unescapeJava

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