Spring 学习笔记 - Spring Expression Language (SpEL) 表达式

水深无声 2022-10-22 15:54 145阅读 0赞

### Spring 学习笔记 - Spring Expression Language（SpEL）表达式 ###

*  基础运算
 *  调用对象、方法
 *  示例代码
 *  参考资料

# 基础运算 #

变量引用： #name 从当前上下文件中取变量 name 
    算数运算： 加+, 减-, 乘*, 除/, 求余%, 幂^
    逻辑运算： ==, !=, >, >=, <, <=, between
    三目运算： 2>1 ? 真 : 假
    正   则：  str matches regex 例："'123' matches '\d{3}'" 结果 true

# 调用对象、方法 #

解析`html`为`doc`对象，并取出`title`内容

T(org.jsoup.Jsoup).parse(#htmlStr).getElementsByTag("title").text()

解析`url`为`doc`对象，并取出`title`内容

T(org.jsoup.Jsoup).connect('https://blog.csdn.net/jx520/article/details/114948684').get().getElementsByTag("title").text()

# 示例代码 #

演示了：正则、字符串的substring、indexOf

import org.junit.Test;
    import org.springframework.expression.EvaluationContext;
    import org.springframework.expression.Expression;
    import org.springframework.expression.ExpressionParser;
    import org.springframework.expression.spel.standard.SpelExpressionParser;
    import org.springframework.expression.spel.support.SimpleEvaluationContext;
    import org.springframework.expression.spel.support.StandardEvaluationContext;
    import org.springframework.util.Assert;
    
    public class SpELTest { 
        
        String str = "<divclass=\"title-box\"><h1class=\"title-blog\"><ahref=\"https://jerryjin.blog.csdn.net\"style=\"\">湖边的小屋遗址</a></h1><pclass=\"description\"style=\"\">那唐僧内眼凡胎不识妖怪，反护着它……</p></div>";
    
        /** 正则 */
        @Test
        public void spelTest(){ 
            String regex = ".*唐僧.*";
            String condition = "#result matches #expect" ;
            EvaluationContext context = SimpleEvaluationContext.forReadWriteDataBinding().build();
            context.setVariable("result", str);
            context.setVariable("expect", regex);
    
            ExpressionParser parser = new SpelExpressionParser();
            Expression expression = parser.parseExpression(condition);
            Boolean value = expression.getValue(context, Boolean.class);
            System.out.println("=========================================================");
            System.out.println("result: " + str);
            System.out.println("expect: " + regex);
            System.out.println("表达式: " + expression.getExpressionString());
            System.out.println("结 果: " + value);
            
            Assert.isTrue(value, "应该匹配正则： " + regex);
        }
    
        /** 方法 substring 需要 StandardEvaluationContext */
        @Test
        public void spelTestSubstring(){ 
            String expect = "湖边的小屋遗址";
            String condition = "#result.substring(92, 99) == #expect" ;
            
            ExpressionParser parser = new SpelExpressionParser();
            EvaluationContext context = new StandardEvaluationContext();
            context.setVariable("result", str);
            context.setVariable("expect", expect);
            Expression expression = parser.parseExpression(condition);
            Boolean value = expression.getValue(context, Boolean.class);
            
            System.out.println("=========================================================");
            System.out.println("result: " + str);
            System.out.println("expect: " + expect);
            System.out.println("表达式: " + expression.getExpressionString());
            System.out.println("结 果: " + value);
    
            Assert.isTrue(value, ".substring(92, 99) 应该等于： " + expect);
        }    
        
        /** 方法 indexOf 需要 StandardEvaluationContext */
        @Test
        public void spelTestIndexOf(){ 
            Integer expect = 150;
            String condition = "#result.indexOf('反护着它') == #expect";
            
            ExpressionParser parser = new SpelExpressionParser();
            EvaluationContext context = new StandardEvaluationContext();
            context.setVariable("result", str);
            context.setVariable("expect", expect);
            Expression expression = parser.parseExpression(condition);
            Boolean value = expression.getValue(context, Boolean.class);
    
            System.out.println("=========================================================");
            System.out.println("result: " + str);
            System.out.println("expect: " + expect);
            System.out.println("表达式: " + expression.getExpressionString());
            System.out.println("结 果: " + value);
    
            Assert.isTrue(value, ".indexOf('反护着它') 应该等于： " + expect);
        }
        
    }

# 参考资料 #

[Spring Expression Language (SpEL)][Spring Expression Language _SpEL]

[Spring 5 中文解析之核心篇-表达式(SpEL)][Spring 5 _-_SpEL]

[Spring Expression Language _SpEL]: https://docs.spring.io/spring-framework/docs/current/reference/html/core.html#expressions
[Spring 5 _-_SpEL]: https://blog.csdn.net/liyong1028826685/article/details/108051895