五.Spring 表达式语言

梦里梦外; 2022-06-17 13:49 147阅读 0赞

为类属性赋值:尽量少用，除非传统很艰难  
**一.入门DEMO**  
步骤解析：  
创建解析器  
解析表达式  
构造上下文  
求值

ExpressionParser parser = new SpelExpressionParser();  
    Expression expression =  parser.parseExpression("('Hello' + ' World').concat(#end)");  
    EvaluationContext context = new StandardEvaluationContext();  
    context.setVariable("end", "!");  
    System.out.println(expression.getValue(context));

XML：

<bean id="world" class="java.lang.String" >
            <constructor-arg value="#{' World!'}" />
    </bean>
    
    <bean id="hello1" class="java.lang.String" >
        <constructor-arg value="#{'Hello'}#{world}" />
    </bean>
    <bean id="hello2" class="java.lang.String" >
            <constructor-arg value="#{'Hello' + world}" />
            
    </bean>
    
        <bean id="hello3" class="java.lang.String" >
            <constructor-arg value="#{'Hello' + @world}" />
        </bean>
    
    ApplicationContext ctx = 
                    new ClassPathXmlApplicationContext("conf/conf-spel.xml");
            String hello1 = ctx.getBean("hello1", String.class);
    注解风格：

@Value(“\#\{‘Hello ’ + world\}”)  
private String value;

public static void main(String[] args) {
            ApplicationContext ctx = new ClassPathXmlApplicationContext("conf/conf-spel.xml");
            AnnoExpression helloBean1 = ctx.getBean("helloBean1", AnnoExpression.class);
            AnnoExpression helloBean2 = ctx.getBean("helloBean2", AnnoExpression.class);
            System.out.println("helloBean1 : " + helloBean1.getValue());
            System.out.println("helloBean2 : " + helloBean2.getValue());
    
    
        }
    XML指定属性值会覆盖注解注入值
    **二.引用Bean本身、Bean的属性以及Bean的方法**
    引用Bean的属性：
    <bean id="carl"      class="com.jike.***.Instrumentalist"> 
              <property name="song" value="#{kenny.song}" /> 
    </bean> 
    等同
    Instrumentalist carl = new Instrumentalist();  
    carl.setSong(kenny.getSong());
    引用Bean方法：
    <property name="song" value="#{songSelector.selectSong()}"/>
    <property name="song" value="#{songSelector.selectSong().toUpperCase()}"/> 
    <property name="song" value="#{songSelector.selectSong()?.toUpperCase()}"/>
    **三.运算符**
    等于：eq    
    小于：lt
    小于等于：le
    大于：gt
    大于等于：ge
    三目运算符：<property name="instrument"  value="#{songSelector.selectSong()=='Jingle Bells'?piano:saxophone}” />

**四.集合操作**

“\`