[BAEL-9235] - Introduction to MVEL

mvel/pom.xml

@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>mvel</artifactId>
+    <name>mvel</name>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.mvel</groupId>
+            <artifactId>mvel2</artifactId>
+            <version>${mvel.version}</version>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <mvel.version>2.5.2.Final</mvel.version>
+    </properties>
+
+</project>

mvel/src/main/java/com/baeldung/mvel/model/Employee.java

@@ -0,0 +1,85 @@
+package com.baeldung.mvel.model;
+
+public class Employee {
+    private String name;
+    private Job job;
+
+    public Employee(String name, Job job) {
+        this.name = name;
+        this.job = job;
+    }
+
+    public Employee(String name, int experienceInYears, double salary, String department) {
+        this.name = name;
+        this.job = new Job(experienceInYears, salary, department);
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public void setJob(Job job) {
+        this.job = job;
+    }
+
+    public Job getJob() {
+        return job;
+    }
+
+
+    public static class Job {
+        private int experienceInYears;
+        private double salary;
+        private String department;
+
+        public Job(int experienceInYears, double salary) {
+            this.experienceInYears = experienceInYears;
+            this.salary = salary;
+        }
+
+        public Job(int experienceInYears, double salary, String department) {
+            this.experienceInYears = experienceInYears;
+            this.salary = salary;
+            this.department = department;
+        }
+
+        public int getExperienceInYears() {
+            return experienceInYears;
+        }
+
+        public void setExperienceInYears(int experienceInYears) {
+            this.experienceInYears = experienceInYears;
+        }
+
+        public double getSalary() {
+            return salary;
+        }
+
+        public void setSalary(double salary) {
+            this.salary = salary;
+        }
+
+        public String getDepartment() {
+            return department;
+        }
+
+        public void setDepartment(String department) {
+            this.department = department;
+        }
+
+        public double calculateAnnualBonus() {
+            if (experienceInYears > 10) {
+                return salary * 0.20;
+            } else if (experienceInYears > 5) {
+                return salary * 0.10;
+            } else {
+                return salary * 0.05;
+            }
+        }
+    }
+
+}

mvel/src/test/java/com/baeldung/mvel/MvelServiceUnitTest.java

@@ -0,0 +1,142 @@
+package com.baeldung.mvel;
+
+import com.baeldung.mvel.model.Employee;
+import org.junit.jupiter.api.Test;
+import org.mvel2.MVEL;
+
+import java.io.Serializable;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class MvelServiceUnitTest {
+
+    @Test
+    public void givenSimpleExpression_whenEvaluate_thenCorrectResult() {
+        String expression = "5 + 3 * 2";
+        Object result = MVEL.eval(expression);
+
+        assertEquals(11, result);
+    }
+
+    @Test
+    public void givenVariables_whenEvaluateExpression_thenCorrectResult() {
+        Map<String, Object> variables = new HashMap<>();
+        variables.put("salary", 75000.0);
+        variables.put("experience", 8);
+
+        String expression = "salary * 0.10";
+        Object result = MVEL.eval(expression, variables);
+
+        assertEquals(7500.0, result);
+    }
+
+    @Test
+    public void givenBooleanExpression_whenEvaluate_thenCorrectResult() {
+        Map<String, Object> variables = new HashMap<>();
+        variables.put("experience", 12);
+        variables.put("salary", 95000.0);
+
+        String expression = "experience > 10 && salary > 80000";
+        Object result = MVEL.eval(expression, variables);
+
+        assertTrue((Boolean) result);
+    }
+
+    @Test
+    public void givenNullSafeNavigation_whenPropertyIsNull_thenNoException() {
+        Employee.Job job = new Employee.Job(5, 5000);
+        Employee employee = new Employee("David", job);
+        employee.getJob().setDepartment(null);
+        String expression = " (job.?department.length) ";
+        Object result = MVEL.eval(expression, employee);
+
+        assertNull(result);
+    }
+
+    @Test
+    public void givenEmployee_whenAccessProperties_thenCorrectValues() {
+        Employee.Job job = new Employee.Job(8, 75000.0);
+        Employee employee = new Employee("John Doe", job);
+
+        String expression = "name + ' has ' + job.experienceInYears + ' years of experience'";
+        Object result = MVEL.eval(expression, employee);
+
+        assertEquals("John Doe has 8 years of experience", result);
+    }
+
+    @Test
+    public void givenEmployee_whenCallMethod_thenCorrectResult() {
+        Employee.Job job = new Employee.Job(12, 90000.0);
+        Employee employee = new Employee("Jane Smith", job);
+
+        String expression = "job.calculateAnnualBonus()";
+        Object result = MVEL.eval(expression, employee);
+
+        assertEquals(18000.0, (Double) result, 0.01);
+    }
+
+    @Test
+    public void givenEmployee_whenEvaluateConditional_thenCorrectResult() {
+        Employee.Job job = new Employee.Job(15, 120000.0);
+        Employee employee = new Employee("Bob Johnson", job);
+
+        String expression = "if (job.experienceInYears > 10) { job.salary * 0.20 } " +
+                "else if (job.experienceInYears > 5) { job.salary * 0.10 } " +
+                "else { job.salary * 0.05 }";
+        Object result = MVEL.eval(expression, employee);
+
+        assertEquals(24000.0, (Double) result, 0.01);
+    }
+
+    @Test
+    public void givenCompiledExpression_whenExecuteMultipleTimes_thenCorrectResults() {
+        String expression = "job.experienceInYears > 5 && job.salary > 50000";
+        Serializable compiledExpression = MVEL.compileExpression(expression);
+
+        Employee.Job job1 = new Employee.Job(7, 60000.0);
+        Employee employee1 = new Employee("Alice", job1);
+
+        Employee.Job job2 = new Employee.Job(3, 45000.0);
+        Employee employee2 = new Employee("Charlie",job2);
+
+        boolean result1 = (Boolean) MVEL.executeExpression(compiledExpression, employee1);
+        boolean result2 = (Boolean) MVEL.executeExpression(compiledExpression, employee2);
+
+        assertTrue(result1);
+        assertFalse(result2);
+    }
+
+    @Test
+    public void givenListProjection_whenFilter_thenCorrectResult() {
+        Map<String, Object> variables = new HashMap<>();
+        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+        variables.put("numbers", numbers);
+
+        String expression = "($ in numbers if $ > 5)";
+        Object result = MVEL.eval(expression, variables);
+
+        assertInstanceOf(List.class, result);
+        List<?> filteredList = (List<?>) result;
+        assertEquals(5, filteredList.size());
+    }
+
+    @Test
+    public void givenListTransformation_whenProject_thenCorrectResult() {
+        Map<String, Object> variables = new HashMap<>();
+        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
+        variables.put("numbers", numbers);
+
+        String expression = "($ * 2 in numbers)";
+        Object result = MVEL.eval(expression, variables);
+
+        assertInstanceOf(List.class, result);
+        List<?> transformedList = (List<?>) result;
+        assertEquals(10, transformedList.get(4));
+    }
+
+
+}

mvel/src/test/java/com/baeldung/mvel/MvelTemplateServiceUnitTest.java

@@ -0,0 +1,79 @@
+package com.baeldung.mvel;
+
+import com.baeldung.mvel.model.Employee;
+import org.junit.jupiter.api.Test;
+import org.mvel2.templates.CompiledTemplate;
+import org.mvel2.templates.TemplateCompiler;
+import org.mvel2.templates.TemplateRuntime;
+
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class MvelTemplateServiceUnitTest {
+
+    @Test
+    public void givenEmployeeData_whenGenerateReport_thenCorrectOutput() {
+        String template = "Employee Report\n" +
+                "================\n" +
+                "Name: @{name}\n" +
+                "Experience: @{experience} years\n" +
+                "Salary: $@{salary}\n";
+
+        Map<String, Object> variables = new HashMap<>();
+        variables.put("name", "John Doe");
+        variables.put("experience", 12);
+        variables.put("salary", 95000.0);
+
+        CompiledTemplate compiledTemplate = TemplateCompiler.compileTemplate(template);
+        String result = (String) TemplateRuntime.execute(compiledTemplate, variables);
+
+        assertTrue(result.contains("John Doe"));
+        assertTrue(result.contains("12 years"));
+    }
+
+    @Test
+    public void givenSeniorEmployee_whenGenerateReport_thenCorrectStatus() {
+        String template = "Employee Report\n" +
+                "@if{experience > 10}" +
+                "Status: Senior Employee\n" +
+                "@else{}" +
+                "Status: Junior/Mid-level Employee\n" +
+                "@end{}";
+
+        Map<String, Object> variables = new HashMap<>();
+        variables.put("experience", 12);
+
+        CompiledTemplate compiledTemplate = TemplateCompiler.compileTemplate(template);
+        String result = (String) TemplateRuntime.execute(compiledTemplate, variables);
+
+        assertTrue(result.contains("Senior Employee"));
+    }
+
+    @Test
+    public void givenEmployeeList_whenGenerateListReport_thenCorrectOutput() {
+        String template = "Employee List:\n" +
+                "@foreach{emp : employees}" +
+                "- @{emp.name} (@{emp.job.department})\n" +
+                "@end{}";
+
+
+        List<Employee> employees = Arrays.asList(
+                new Employee("John", 10, 80000.0, "IT"),
+                new Employee("Jane", 8, 75000.0, "HR"),
+                new Employee("Bob", 12, 95000.0, "Finance")
+        );
+
+        Map<String, Object> variables = new HashMap<>();
+        variables.put("employees", employees);
+
+        CompiledTemplate compiledTemplate = TemplateCompiler.compileTemplate(template);
+        String result = (String) TemplateRuntime.execute(compiledTemplate, variables);
+
+        assertTrue(result.contains("John (IT)"));
+        assertTrue(result.contains("Jane (HR)"));
+    }
+}

pom.xml

@@ -744,6 +744,7 @@
                 <module>metrics</module>
                 <module>microservices-modules</module>
                 <module>mustache</module>
+                <module>mvel</module>
                 <module>mybatis</module>
                 <module>mybatis-plus</module>
                 <module>netflix-modules</module>
@@ -1226,6 +1227,7 @@
                 <module>metrics</module>
                 <module>microservices-modules</module>
                 <module>mustache</module>
+                <module>mvel</module>
                 <module>mybatis</module>
                 <module>mybatis-plus</module>
                 <module>netflix-modules</module>