BAEL-5940 code for the object validation after deserialization article

javax-validation-advanced/src/main/java/com/baeldung/javaxval/afterdeserialization/BeanDeserializerModifierWithValidation.java

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+package com.baeldung.javaxval.afterdeserialization;
+
+import com.fasterxml.jackson.databind.BeanDescription;
+import com.fasterxml.jackson.databind.DeserializationConfig;
+import com.fasterxml.jackson.databind.JsonDeserializer;
+import com.fasterxml.jackson.databind.deser.BeanDeserializer;
+import com.fasterxml.jackson.databind.deser.BeanDeserializerModifier;
+
+public class BeanDeserializerModifierWithValidation extends BeanDeserializerModifier {
+
+    @Override
+    public JsonDeserializer<?> modifyDeserializer(DeserializationConfig config, BeanDescription beanDesc, JsonDeserializer<?> deserializer) {
+        if (deserializer instanceof BeanDeserializer) {
+            return new BeanDeserializerWithValidation((BeanDeserializer) deserializer);
+        }
+
+        return deserializer;
+    }
+
+}

javax-validation-advanced/src/main/java/com/baeldung/javaxval/afterdeserialization/BeanDeserializerWithValidation.java

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+package com.baeldung.javaxval.afterdeserialization;
+
+import java.io.IOException;
+import java.util.Set;
+
+import javax.validation.ConstraintViolation;
+import javax.validation.ConstraintViolationException;
+import javax.validation.Validation;
+import javax.validation.Validator;
+import javax.validation.ValidatorFactory;
+
+import com.fasterxml.jackson.core.JsonParser;
+import com.fasterxml.jackson.databind.DeserializationContext;
+import com.fasterxml.jackson.databind.deser.BeanDeserializer;
+import com.fasterxml.jackson.databind.deser.BeanDeserializerBase;
+
+public class BeanDeserializerWithValidation extends BeanDeserializer {
+
+    private static final ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
+    private static final Validator validator = factory.getValidator();
+
+    protected BeanDeserializerWithValidation(BeanDeserializerBase src) {
+        super(src);
+    }
+
+    @Override
+    public Object deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
+        Object instance = super.deserialize(p, ctxt);
+        validate(instance);
+        return instance;
+    }
+
+    public <T> void validate(T t) {
+        Set<ConstraintViolation<T>> violations = validator.validate(t);
+        if (!violations.isEmpty()) {
+            throw new ConstraintViolationException(violations);
+        }
+    }
+
+}

javax-validation-advanced/src/main/java/com/baeldung/javaxval/afterdeserialization/Student.java

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+package com.baeldung.javaxval.afterdeserialization;
+
+import javax.validation.constraints.Size;
+
+public class Student {
+
+    @Size(min = 5, max = 10, message = "Student's name must be between 5 and 10 characters")
+    private String name;
+
+    public String getName() {
+        return name;
+    }
+
+}

javax-validation-advanced/src/main/java/com/baeldung/javaxval/afterdeserialization/StudentDeserializerWithValidation.java

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+package com.baeldung.javaxval.afterdeserialization;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.module.SimpleModule;
+
+public class StudentDeserializerWithValidation {
+
+    public static Student readStudent(InputStream inputStream) throws IOException {
+        ObjectMapper mapper = getObjectMapperWithValidation();
+        return mapper.readValue(inputStream, Student.class);
+    }
+
+    private static ObjectMapper getObjectMapperWithValidation() {
+        SimpleModule validationModule = new SimpleModule();
+        validationModule.setDeserializerModifier(new BeanDeserializerModifierWithValidation());
+        ObjectMapper mapper = new ObjectMapper();
+        mapper.registerModule(validationModule);
+        return mapper;
+    }
+
+}

javax-validation-advanced/src/test/java/com/baeldung/javaxval/StudentDeserializerWithValidationUnitTest.java

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+package com.baeldung.javaxval;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+import javax.validation.ConstraintViolationException;
+
+import org.junit.jupiter.api.Test;
+
+import com.baeldung.javaxval.afterdeserialization.Student;
+import com.baeldung.javaxval.afterdeserialization.StudentDeserializerWithValidation;
+
+public class StudentDeserializerWithValidationUnitTest {
+
+    private final String EXPECTED_ERROR_MESSAGE = "name: Student's name must be between 5 and 10 characters";
+    private final String EXPECTED_STUDENT_NAME = "Daniel";
+    private final String NAME_TOO_LONG_STUDENT_FILE = "nameTooLongStudent.json";
+    private final String NAME_TOO_SHORT_STUDENT_FILE = "nameTooShortStudent.json";
+    private final String SUBDIRECTORY = "afterdeserialization/";
+    private final String VALID_STUDENT_FILE = "validStudent.json";
+
+    @Test
+    void givenValidStudent_WhenReadStudent_ThenReturnStudent() throws IOException {
+        InputStream inputStream = getInputStream(VALID_STUDENT_FILE);
+        Student result = StudentDeserializerWithValidation.readStudent(inputStream);
+        assertEquals(EXPECTED_STUDENT_NAME, result.getName());
+    }
+
+    @Test
+    void givenStudentWithTooShortName_WhenReadStudent_ThenThrows() {
+        InputStream inputStream = getInputStream(NAME_TOO_SHORT_STUDENT_FILE);
+        ConstraintViolationException constraintViolationException = assertThrows(ConstraintViolationException.class, () -> StudentDeserializerWithValidation.readStudent(inputStream));
+        assertEquals(EXPECTED_ERROR_MESSAGE, constraintViolationException.getMessage());
+    }
+
+    @Test
+    void givenStudentWithTooLongName_WhenReadStudent_ThenThrows() {
+        InputStream inputStream = getInputStream(NAME_TOO_LONG_STUDENT_FILE);
+        ConstraintViolationException constraintViolationException = assertThrows(ConstraintViolationException.class, () -> StudentDeserializerWithValidation.readStudent(inputStream));
+        assertEquals(EXPECTED_ERROR_MESSAGE, constraintViolationException.getMessage());
+    }
+
+    private InputStream getInputStream(String fileName) {
+        return getClass().getClassLoader()
+            .getResourceAsStream(SUBDIRECTORY + fileName);
+    }
+
+}

javax-validation-advanced/src/test/resources/afterdeserialization/nameTooLongStudent.json

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+{
+  "name": "Constantine"
+}

javax-validation-advanced/src/test/resources/afterdeserialization/nameTooShortStudent.json

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+{
+  "name": "Max"
+}

javax-validation-advanced/src/test/resources/afterdeserialization/validStudent.json

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+{
+  "name": "Daniel"
+}