Application example of ExpressionUtil tool class

What is ExpressionUtil

ExpressionUtil is a tool class that handles expression-related operations. It provides some methods to facilitate users to process expression-related calculations, comparisons, conversions and other operations in the program. For example, you can use ExpressionUtil to calculate the result of a mathematical expression, compare whether the values ​​of two expressions are equal, convert a string expression into executable code, etc. ExpressionUtil simplifies the development process and improves the readability and maintainability of the code.

What can be done

ExpressionUtil is an expression processing tool class that can be used to parse, calculate and convert mathematical expressions.

• Analytical expressions: Mathematical expression strings can be parsed into expression objects to facilitate subsequent calculations and operations.

• Calculate expression: You can calculate the expression and get the result. Supports basic mathematical operators (addition, subtraction, multiplication and division) and functions (such as sin, cos, sqrt, etc.).

• Expression conversion: You can convert an expression object to a string form, or convert an expression in a string form to an expression object. This makes it easy to use expressions in different scenarios.

• Variable replacement: You can replace the variable in the expression to a specific numerical value, thereby realizing the calculation of expressions with variables.

• Error handling: It can detect and handle illegal expressions, such as bracket mismatch, operator errors, etc.

What APIs are there

• evaluate(String expression): evaluates the specified expression and returns the result.

• evaluate(Expression expression): evaluates the passed expression object and returns the result.

• parse(String expression): parse the specified string expression into an expression object.

• isValid(String expression): Checks whether the specified expression is legal.

• simplify(Expression expression): simplifies the process of the incoming expression object to minimize the complexity of the expression.

• differentiate(Expression expression, String variable): performs differential calculations on the passed expression object to obtain the derivative of the specified variable.

• integrate(Expression expression, String variable): performs integral calculation on the passed expression object to obtain the original function about the specified variable.

• substitute(Expression expression, Map<String, Double> variables): Replace the variable in the passed expression object with the specified value and return the new expression object.

Example

Dependencies that need to be introduced

<dependency>
    <groupId></groupId>
    <artifactId>mvel2</artifactId>
    <version>2.4.</version>
</dependency>

Use the ExpressionUtil tool class to evaluate expressions:

• Use multiple variables:

String ruleExpress = "age > 18 && gender == 'male' && height > 160";
Map<String, Object> map = new HashMap<String, Object>();
("age", 19);
("gender", "male");
("height", 170);
Boolean eval = (Boolean) (ruleExpress, map);
(eval); // Output: true

• Comparison with strings：

String ruleExpress = "('John') && ('New York')";
Map<String, Object> map = new HashMap<String, Object>();
("name", "John");
("city", "new york");
Boolean eval = (Boolean) (ruleExpress, map);
(eval); // Output: true

• Use the computed expression:

String ruleExpress = "score * weight >= 80";
Map<String, Object> map = new HashMap<String, Object>();
("score", 90);
("weight", 0.9);
Boolean eval = (Boolean) (ruleExpress, map);
(eval); // Output: true

Summarize

• Expression parsing:

  • parse(String expression): parses a string expression into oneExpressionObject. This method parses the expression based on the syntax rules and returns an object representing the expression.

• Expression calculation:

  • evaluate(Expression expression): Calculate the given expression object and return the calculation result. This method will perform corresponding calculation operations based on the type of expression and operators, and return the calculation result.
  • evaluate(String expression): parses a string expression into oneExpressionObject, and calculate it, and return the calculation result.

• Expression evaluation:

  • evaluateBoolean(Expression expression): Evaluate the given expression object and return an evaluation result of a Boolean type. This method converts the expression to a Boolean value based on the evaluation result, and returns the evaluation result.
  • evaluateBoolean(String expression): parses a string expression into oneExpressionObject, evaluate it, and return a Boolean type evaluation result.

• Expression optimization:

  • optimize(Expression expression): Optimize the given expression object and return the optimized expression object. This method will optimize operations based on the structure and logic of the expression to improve the computational efficiency and performance of the expression.

• Expression conversion:

  • convertToString(Expression expression): Convert the given expression object to a string expression and return the string result. This method converts the expression object into the corresponding string expression based on the type and structure of the expression object and returns the string result.

• Expression verification:

  • validate(Expression expression): Verify the given expression object and check whether it complies with syntax rules and logical requirements. This method performs corresponding verification operations based on the type and operator of the expression and returns the verification result.

This is the end of this article about the ExpressionUtil tool application. For more related ExpressionUtil application content, please search for my previous articles or continue browsing the related articles below. I hope everyone will support me in the future!

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