MVEL“in”运算符不适用于java中的集合

Question

我试图在代码中使用MVEL“in”运算符来计算表达式

List<String> countriesAvailable = new ArrayList<String>();
countriesAvailable.add("Australia");
countriesAvailable.add("France");
List<String> countriesVisited = new ArrayList<String>();
countriesVisited.add("Austria");
countriesVisited.add("France");
Map<String, List<String>> vars = new HashMap<String, List<String>>();
vars.put("countriesAvailable", countriesAvailable);
vars.put("countriesVisited", countriesVisited);
Boolean s = (Boolean) MVEL.eval("countriesVisited in countriesAvailable", vars);
System.out.println(s);

给出错误：语法错误或不兼容类型

Answer 1

这是解决办法。您需要使用containsAll

还请注意，您在第二个列表中拼错了澳大利亚。我不确定这是否是为了检查评估

    List<String> countriesAvailable = new ArrayList<String>();
    countriesAvailable.add("Australia");
    countriesAvailable.add("France");

    List<String> countriesVisited = new ArrayList<String>();
    countriesVisited.add("Austria");
    countriesVisited.add("France");

    Map<String, List<String>> vars = new HashMap<String, List<String>>();
    vars.put("countriesAvailable", countriesAvailable);
    vars.put("countriesVisited", countriesVisited);

    Boolean s = (Boolean) MVEL.eval(
            "countriesAvailable.containsAll(countriesVisited)", vars);

    System.out.println("Result = " + s);

Result = false

您还可以使用java.util.Collections执行不相交。从反面来看

Boolean s = 
   (Boolean) MVEL.eval(
         "!java.util.Collections.disjoint(countriesAvailable,countriesVisited)",
         vars);

Result = true