[BAEL-3019] Add sample code for empty and blank string checks (#7176)

* [BAEL-3019] Add sample code for empty and blank string checks

* [BAEL-3019] Add article link to module README

* [BAEL-3019] Remove blank line in the beginning of certain tests

* [BAEL-3019] Unroll tests and adhere to givenXXX_thenXXX naming convention

* Revert "[BAEL-3019] Add article link to module README"

This reverts commit 675295fafa53861d2bd3eb0e766665a58adda97d.

* [BAEL-3019] Bump guava version for 'java-strings-2' to 28.0-jre

java-strings-2/pom.xml

@@ -57,6 +57,26 @@
             <artifactId>commons-text</artifactId>
             <version>${commons-text.version}</version>
         </dependency>
+        <dependency>
+            <groupId>javax.validation</groupId>
+            <artifactId>validation-api</artifactId>
+            <version>2.0.0.Final</version>
+        </dependency>
+        <dependency>
+            <groupId>org.hibernate.validator</groupId>
+            <artifactId>hibernate-validator</artifactId>
+            <version>6.0.2.Final</version>
+        </dependency>
+        <dependency>
+            <groupId>javax.el</groupId>
+            <artifactId>javax.el-api</artifactId>
+            <version>3.0.0</version>
+        </dependency>
+        <dependency>
+            <groupId>org.glassfish.web</groupId>
+            <artifactId>javax.el</artifactId>
+            <version>2.2.6</version>
+        </dependency>
 
     </dependencies>
 
@@ -86,7 +106,7 @@
     <properties>
         <commons-lang3.version>3.8.1</commons-lang3.version>
         <icu4j.version>61.1</icu4j.version>
-        <guava.version>27.0.1-jre</guava.version>
+        <guava.version>28.0-jre</guava.version>
         <commons-text.version>1.4</commons-text.version>
     </properties>
 

java-strings-2/src/main/java/com/baeldung/string/emptystrings/EmptyStringCheck.java

@@ -0,0 +1,8 @@
+package com.baeldung.string.emptystrings;
+
+class EmptyStringCheck {
+
+    boolean isEmptyString(String string) {
+        return string == null || string.isEmpty();
+    }
+}

java-strings-2/src/main/java/com/baeldung/string/emptystrings/Java5EmptyStringCheck.java

@@ -0,0 +1,8 @@
+package com.baeldung.string.emptystrings;
+
+class Java5EmptyStringCheck {
+
+    boolean isEmptyString(String string) {
+        return string == null || string.length() == 0;
+    }
+}

java-strings-2/src/main/java/com/baeldung/string/emptystrings/PlainJavaBlankStringCheck.java

@@ -0,0 +1,8 @@
+package com.baeldung.string.emptystrings;
+
+class PlainJavaBlankStringCheck {
+
+    boolean isBlankString(String string) {
+        return string == null || string.trim().isEmpty();
+    }
+}

java-strings-2/src/main/java/com/baeldung/string/emptystrings/SomeClassWithValidations.java

@@ -0,0 +1,14 @@
+package com.baeldung.string.emptystrings;
+
+import javax.validation.constraints.Pattern;
+
+class SomeClassWithValidations {
+
+    @Pattern(regexp = "\\A(?!\\s*\\Z).+")
+    private String someString;
+
+    SomeClassWithValidations setSomeString(String someString) {
+        this.someString = someString;
+        return this;
+    }
+}

java-strings-2/src/test/java/com/baeldung/string/emptystrings/EmptyStringsUnitTest.java

@@ -0,0 +1,142 @@
+package com.baeldung.string.emptystrings;
+
+import static org.hamcrest.Matchers.iterableWithSize;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertThat;
+import static org.junit.Assert.assertTrue;
+
+import java.util.Set;
+
+import javax.validation.ConstraintViolation;
+import javax.validation.Validation;
+import javax.validation.Validator;
+import javax.validation.ValidatorFactory;
+
+import org.apache.commons.lang3.StringUtils;
+import org.junit.Test;
+
+import com.google.common.base.Strings;
+
+public class EmptyStringsUnitTest {
+
+    private String emptyString = "";
+    private String blankString = "  \n\t  ";
+    private String nonEmptyString = "   someString   ";
+
+    /*
+     * EmptyStringCheck
+     */
+    @Test
+    public void givenSomeEmptyString_thenEmptyStringCheckIsEmptyStringReturnsTrue() {
+        assertTrue(new EmptyStringCheck().isEmptyString(emptyString));
+    }
+
+    @Test
+    public void givenSomeNonEmptyString_thenEmptyStringCheckIsEmptyStringReturnsFalse() {
+        assertFalse(new EmptyStringCheck().isEmptyString(nonEmptyString));
+    }
+
+    @Test
+    public void givenSomeBlankString_thenEmptyStringCheckIsEmptyStringReturnsFalse() {
+        assertFalse(new EmptyStringCheck().isEmptyString(blankString));
+    }
+
+    /*
+     * Java5EmptyStringCheck
+     */
+    @Test
+    public void givenSomeEmptyString_thenJava5EmptyStringCheckIsEmptyStringReturnsTrue() {
+        assertTrue(new Java5EmptyStringCheck().isEmptyString(emptyString));
+    }
+
+    @Test
+    public void givenSomeNonEmptyString_thenJava5EmptyStringCheckIsEmptyStringReturnsFalse() {
+        assertFalse(new Java5EmptyStringCheck().isEmptyString(nonEmptyString));
+    }
+
+    @Test
+    public void givenSomeBlankString_thenJava5EmptyStringCheckIsEmptyStringReturnsFalse() {
+        assertFalse(new Java5EmptyStringCheck().isEmptyString(blankString));
+    }
+
+    /*
+     * PlainJavaBlankStringCheck
+     */
+    @Test
+    public void givenSomeEmptyString_thenPlainJavaBlankStringCheckIsBlankStringReturnsTrue() {
+        assertTrue(new PlainJavaBlankStringCheck().isBlankString(emptyString));
+    }
+
+    @Test
+    public void givenSomeNonEmptyString_thenPlainJavaBlankStringCheckIsBlankStringReturnsFalse() {
+        assertFalse(new PlainJavaBlankStringCheck().isBlankString(nonEmptyString));
+    }
+
+    @Test
+    public void givenSomeBlankString_thenPlainJavaBlankStringCheckIsBlankStringReturnsTrue() {
+        assertTrue(new PlainJavaBlankStringCheck().isBlankString(blankString));
+    }
+
+    /*
+     * Apache Commons Lang StringUtils
+     */
+    @Test
+    public void givenSomeEmptyString_thenStringUtilsIsBlankReturnsTrue() {
+        assertTrue(StringUtils.isBlank(emptyString));
+    }
+
+    @Test
+    public void givenSomeNonEmptyString_thenStringUtilsIsBlankReturnsFalse() {
+        assertFalse(StringUtils.isBlank(nonEmptyString));
+    }
+
+    @Test
+    public void givenSomeBlankString_thenStringUtilsIsBlankReturnsTrue() {
+        assertTrue(StringUtils.isBlank(blankString));
+    }
+
+    /*
+     * Google Guava Strings
+     */
+    @Test
+    public void givenSomeEmptyString_thenStringsIsNullOrEmptyStringReturnsTrue() {
+        assertTrue(Strings.isNullOrEmpty(emptyString));
+    }
+
+    @Test
+    public void givenSomeNonEmptyString_thenStringsIsNullOrEmptyStringReturnsFalse() {
+        assertFalse(Strings.isNullOrEmpty(nonEmptyString));
+    }
+
+    @Test
+    public void givenSomeBlankString_thenStringsIsNullOrEmptyStringReturnsFalse() {
+        assertFalse(Strings.isNullOrEmpty(blankString));
+    }
+
+    /*
+     * Bean Validation
+     */
+    private ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
+    private Validator validator = factory.getValidator();
+
+    @Test
+    public void givenSomeEmptyString_thenBeanValidationReturnsViolations() {
+        SomeClassWithValidations someClassWithValidations = new SomeClassWithValidations().setSomeString(emptyString);
+        Set<ConstraintViolation<SomeClassWithValidations>> violations = validator.validate(someClassWithValidations);
+        assertThat(violations, iterableWithSize(1));
+    }
+
+    @Test
+    public void givenSomeNonEmptyString_thenBeanValidationValidatesWithoutViolations() {
+        SomeClassWithValidations someClassWithValidations = new SomeClassWithValidations().setSomeString(nonEmptyString);
+        Set<ConstraintViolation<SomeClassWithValidations>> violations = validator.validate(someClassWithValidations);
+        assertThat(violations, iterableWithSize(0));
+    }
+
+    @Test
+    public void givenSomeBlankString_thenBeanValidationReturnsViolations() {
+        SomeClassWithValidations someClassWithValidations = new SomeClassWithValidations().setSomeString(blankString);
+        Set<ConstraintViolation<SomeClassWithValidations>> violations = validator.validate(someClassWithValidations);
+        assertThat(violations, iterableWithSize(1));
+    }
+}