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Java evaluate string as expression or code execution – Apache

Say , i have List of Emp object with name, age and salary attribute . 

List<Emp> empObj = readEmpDetails();

Keeping filter condition from DB or read from flat file. But syntax like below format.

name contains mike
age gt 100

How can i convert list of above condition to java expression . need to perform this condition against empObj which we read from DB source. How can i do this ? Please share your experience.

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2

Answers


  1. 0

    Based on your request, I’ll make code like the following.

    public boolean filter(String name, String search, int age) {
    boolean a = name.contains(search/* mike */);
    boolean b = (age >= 100);
    return a & b;
}

    The following code is second way after I checked you reply.

    public ArrayList<Emp> filter() {
    ArrayList<Emp> results = new ArrayList<>();

    this.emps.stream()
            .filter(Main::wordFilterFunc)
            .filter(Main::ageFilterFunc)
            .forEach(emp -> results.add(emp));

    return results;
}

private static boolean wordFilterFunc(Emp word){
    // implement what you want
}

private static boolean ageFilterFunc(Emp word){
    // implement what you want
}
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  2. 0

    You could use Spring Spel (org.springframework.expression.ExpressionParser):

    public static void main(String[] args) {
    List<Emp> emp = Arrays.asList(new Emp("Ann", 25, 1000L)
            ,new Emp("John", 40, 2000L)
            ,new Emp("Alex", 60, 3000L));
    ExpressionParser parser = new SpelExpressionParser();

    Expression exp = parser.parseExpression("age gt 30");


    emp.stream()
            .filter(emp1 -> exp.getValue(emp1, Boolean.class))
            .forEach(emp1 -> System.out.println(emp1.getName() + " " + emp1.getAge()));
}

    Output:

    John 40
Alex 60

    Types of literals and operations are:

    • Literals:
      • Text literals: ‘one text’, ‘Another one!’,…
      • Number literals: 0, 34, 3.0, 12.3,…
      • Boolean literals: true, false
      • Null literal: null
      • Literal tokens: one, sometext, main,…
    • Text operations:
      • String concatenation: +
      • Literal substitutions: |The name is ${name}|
    • Arithmetic operations:
      • Binary operators: +, -, *, /, %
      • Minus sign (unary operator): –
    • Boolean operations:
      • Binary operators: and, or
      • Boolean negation (unary operator): !, not
    • Comparisons and equality:
      • Comparators: >, <, >=, <= (gt, lt, ge, le)
      • Equality operators: ==, != (eq, ne)
    • Conditional operators:
      • If-then: (if) ? (then)
      • If-then-else: (if) ? (then) : (else)
      • Default: (value) ?: (defaultvalue)
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