Java 常用类型系列（三）字符串类型总结

发表于 2018-04-04 更新于 2023-02-21 阅读次数：

继承结构

methods_of_CharSequence

Appendable

CharSequence

字符串的实现

history_of_String

字符串的创建方式

通过字符串常量创建

通过构造方法创建

`intern()` 方法

字符串的处理

字符串拼接

字符串拼接的三种方式，区别如下：

	since	immutable ?	thread-safe ?
`java.lang.String`	Java SE 1.0	immutable	no thread-safe
`java.lang.StringBuffer`	Java SE 1.0	mutable	thread-safe
`java.lang.StringBuilder`	Java SE 1.5	mutable	no thread-safe

字符串拼接的字节码分析，参考：《On Java 8》第十八章字符串：+ 的重载与 StringBuilder 对比

除了上述方式之外， Java SE 8 还提供了新的工具类 java.util.StringJoiner，它是String.join 和 java.util.stream.Collectors#joining(...) 的底层实现。结合 Stream API 使用如下：

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2
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// [a,b,c,d,e,f,g]
Arrays.asList("a", "b", "c", "d", "e", "f", "g").stream()
                .collect(Collectors.joining(",", "[", "]"));

字符串格式化

java.util.Formatter —— C 语言 printf 风格的字符串格式化解释器。

Formatter

用法：

Returns a formatted string using the specified format string and args.

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String s1 = new Formatter().format(format, args).toString();
// or simplied
String s2 = String.format(format, args);

Writes a formatted string to this output stream using the specified format string and args.

1 2	System.out.printf(format, args); System.out.format(format, args);

参考：

https://linux.die.net/man/1/printf

https://linux.die.net/man/3/printf

https://en.wikipedia.org/wiki/Printf_format_string

https://www.baeldung.com/linux/printf-echo

$ printf "%s %s" hello world | hexyl
┌────────┬─────────────────────────┬─────────────────────────┬────────┬────────┐
│00000000│ 68 65 6c 6c 6f 20 77 6f ┊ 72 6c 64                │hello wo┊rld     │
└────────┴─────────────────────────┴─────────────────────────┴────────┴────────┘

https://www.baeldung.com/java-printstream-printf

https://blog.csdn.net/quinnnorris/article/details/54614446

字符串转义

方式一：在线工具：https://www.freeformatter.com/string-escaper.html

HTML Escape
Escapes or unescapes an HTML file removing traces of offending characters that could be wrongfully interpreted as markup.

FEATURES
Escapes all reserverd characters with their corresponding HTML entities (‘, “, &, <, >)
Escapes ISO 8859-1 symbols and characters that have corresponding HTML entities

JSON Escape
Escapes or unescapes a JSON string removing traces of offending characters that could prevent parsing.

XML Escape
Escapes or unescapes an XML file removing traces of offending characters that could be wrongfully interpreted as markup.

CSV Escape
Escapes or unescapes a CSV string removing traces of offending characters that could prevent parsing.

JavaScript Escape
Escapes or unescapes a JavaScript string removing traces of offending characters that could prevent interpretation.

Java and .Net Escape
Escapes or unescapes a Java or .Net string removing traces of offending characters that could prevent compiling.

SQL Escape
Escapes or unescapes a SQL string removing traces of offending characters that could prevent execution.

方式二：代码处理

Apache Commons Lang 提供了字符串转义和反转义工具类 org.apache.commons.lang3.StringEscapeUtils，用于 Java、JavaScript、JSON、HTML、XML、CSV 等字符串：

StringEscapeUtils

例如：

// &lt;span&gt;hello world&lt;/span&gt;
StringEscapeUtils.escapeHtml4("<span>hello world</span>");

// {hello: "world"}
StringEscapeUtils.unescapeJson("{hello: \"world\"}");

例如，有些 HTML 字符实体在 PDF 是不支持的，需要先转义：

// flying saucer
ITextRenderer renderer = new ITextRenderer();

String escapedHtml = StringEscapeUtils.escapeHtml4(srcHtml);
renderer.setDocumentFromString(escapedHtml);