Overview

Provides support for evaluating arbitrary artithmetic/logical/string expressions.

How to use?

You create a new ExprExecutor, then call "execute" on it.

String expr = "(3+7)/2*3";
int res = (Integer) executor.execute(expr);
// result is 15

Cool, how about logical compare.

String expr = "(7>3)&&(10>8)";
boolean res = (Boolean) executor.execute(expr, new HashMap<>());

// result is true

That cool, But in addition to simple expressions, conditional branch judgments are possible, there is a case: Grades for student achievement

a score greater than 80 is outstanding, a score greater than 60 is a pass, and a score less than 60 is a fail

we can use this express:

String expr = "case when $$grade>80 then '优秀' when $$grade>60 then '及格' ELSE '不及格' END";
Map<String, Object> parameters = new HashMap<>();
parameters.put("grade", 70);
String res = (String) executor.execute(expr, parameters);

// result is '及格'

Maybe, you param is complex type such as class type, in this case,you can:

public class User{
    private String name;
    private int age;

    public User(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

String expr = "case when $$user.age>60 then '老人' when $$user.age>20 then '成年' ELSE '青年' END";
Map<String, Object> parameters = new HashMap<>();
User user = new User("pioneeryi",30);
parameters.put("user", user);
String res = (String) executor.execute(expr, parameters);

// result is '成年'

Operators support

Arithmetic: + - * /
Comparators: > >= < <= == !=
Logical operator: || &&
CaseWhen: SQL like case when statement
Param: simple type and complex class type

How to expand？

Fist Step: expand grammar

If you wand to expand the expression engine, you first should design you grammar and expand the Antlr4 grammar file.

Second step: Implements AstVisitor