SpEL小试牛刀

SpEL（Spring expression Language），即Spring表达式语言，语言简洁，功能强大。

private static final Cache expression_CACHE = CacheBuilder.newBuilder()
		.maximumSize(8192)
		.initialCapacity(512)
		.expireAfterWrite(1L, TimeUnit.HOURS)
		.build();

	private static final expressionParser SPEL_PARSER = new SpelexpressionParser();

public static String parse(String expression, Map param) {
	return parse(expression, String.class, param);
}

public static  T parse(String expression, Class clazz, Map param) {
	try {
		expression e = expression_CACHE.get(expression, () -> SPEL_PARSER.parseexpression(expression));
		evaluationContext context = new StandardevaluationContext();
		for (Map.Entry entry : param.entrySet()) {
			context.setVariable(entry.getKey(), entry.getValue());
		}
		return e.getValue(context, clazz);
	} catch (ExecutionException e) {
		throw new RuntimeException(e);
	}
}

• 字符常量

// error
String exp = "Const"

// OK
String exp = "'CityList'"  

• 属性变量

String exp = "#cityCode"

• 字符拼接

字符串连接符：+

String exp = "'PRE'+#cityCode+'SUFF'"

String exp = "#cityCode + ':'+ #type"

• 嵌套对象属性

String exp = "#city.code"

String exp = "#city.code+'PRE'+#city.type+#code+'SUFF'"

注意

• 属性为 null会转化为 “null” 字符串
• 嵌套对象外层不能为null，否则抛 SpelevaluationException 异常
• 嵌套对象外层非null，最后一层引用属性为null 则会转化为 "null"字符串

• https://docs.spring.io/spring-framework/docs/current/reference/html/core.html#expressions
• https://www.jianshu.com/p/e0b50053b5d3
• https://www.jianshu.com/p/27fd3754bb9c