BAEL-2399: Guice vs Spring - Dependency Injection

guice/src/main/java/com/baeldung/examples/common/Account.java

@@ -0,0 +1,27 @@
+package com.baeldung.examples.common;
+
+import org.springframework.stereotype.Component;
+
+@Component
+public class Account {
+
+    private String accountNumber;
+    private String type;
+
+    public String getAccountNumber() {
+        return accountNumber;
+    }
+
+    public void setAccountNumber(String accountNumber) {
+        this.accountNumber = accountNumber;
+    }
+
+    public String getType() {
+        return type;
+    }
+
+    public void setType(String type) {
+        this.type = type;
+    }
+
+}

guice/src/main/java/com/baeldung/examples/common/AccountService.java

@@ -0,0 +1,8 @@
+package com.baeldung.examples.common;
+
+import java.util.List;
+
+public interface AccountService {
+    public List<String> listAccountTypes();
+
+}

guice/src/main/java/com/baeldung/examples/common/AccountServiceImpl.java

@@ -0,0 +1,15 @@
+package com.baeldung.examples.common;
+
+import java.util.Arrays;
+import java.util.List;
+
+import org.springframework.stereotype.Component;
+
+@Component
+public class AccountServiceImpl implements AccountService {
+
+    public List<String> listAccountTypes() {
+        return Arrays.asList("Checking", "Saving");
+    }
+
+}

guice/src/main/java/com/baeldung/examples/common/Address.java

@@ -0,0 +1,35 @@
+package com.baeldung.examples.common;
+
+import org.springframework.stereotype.Component;
+
+@Component
+public class Address {
+    private String city;
+    private String state;
+    private String county;
+
+    public String getCity() {
+        return city;
+    }
+
+    public void setCity(String city) {
+        this.city = city;
+    }
+
+    public String getState() {
+        return state;
+    }
+
+    public void setState(String state) {
+        this.state = state;
+    }
+
+    public String getCounty() {
+        return county;
+    }
+
+    public void setCounty(String county) {
+        this.county = county;
+    }
+
+}

guice/src/main/java/com/baeldung/examples/common/BookService.java

@@ -0,0 +1,9 @@
+package com.baeldung.examples.common;
+
+import java.util.List;
+
+public interface BookService {
+
+    public List<String> findBestSellerBooks();
+
+}

guice/src/main/java/com/baeldung/examples/common/BookServiceImpl.java

@@ -0,0 +1,12 @@
+package com.baeldung.examples.common;
+
+import java.util.Arrays;
+import java.util.List;
+
+public class BookServiceImpl implements BookService {
+
+    public List<String> findBestSellerBooks() {
+        return Arrays.asList("Harry Potter", "Lord of The Rings");
+    }
+
+}

guice/src/main/java/com/baeldung/examples/guice/Employee.java

@@ -0,0 +1,32 @@
+package com.baeldung.examples.guice;
+
+import com.google.inject.Inject;
+
+public class Employee {
+
+    private String firstName;
+    private String lastName;
+
+    @Inject
+    public Employee(String firstName) {
+        this.firstName = firstName;
+        this.lastName = "Default";
+    }
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public void setFirstName(String firstName) {
+        this.firstName = firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public void setLastName(String lastName) {
+        this.lastName = lastName;
+    }
+
+}

guice/src/main/java/com/baeldung/examples/guice/Foo.java

@@ -0,0 +1,5 @@
+package com.baeldung.examples.guice;
+
+
+public class Foo {
+}

guice/src/main/java/com/baeldung/examples/guice/FooGenerator.java

@@ -0,0 +1,11 @@
+package com.baeldung.examples.guice;
+
+import org.springframework.lang.Nullable;
+
+import com.google.inject.Inject;
+
+public class FooGenerator {
+    @Inject
+    public FooGenerator(@Nullable Foo foo) {
+    }
+}

guice/src/main/java/com/baeldung/examples/guice/GuiceUser.java

@@ -0,0 +1,32 @@
+package com.baeldung.examples.guice;
+
+import com.baeldung.examples.common.Account;
+import com.baeldung.examples.common.Address;
+import com.google.inject.Inject;
+
+public class GuiceUser {
+
+    @Inject
+    private Account account;
+
+    private Address address;
+
+    public Account getAccount() {
+        return account;
+    }
+
+    public void setAccount(Account account) {
+        this.account = account;
+    }
+
+    public Address getAddress() {
+        return address;
+    }
+
+    @Inject
+    public void setAddress(Address address) {
+        this.address = address;
+        address.setCity("Default");
+    }
+
+}

guice/src/main/java/com/baeldung/examples/guice/GuiceUserService.java

@@ -0,0 +1,19 @@
+package com.baeldung.examples.guice;
+
+import com.baeldung.examples.common.AccountService;
+import com.google.inject.Inject;
+
+public class GuiceUserService {
+
+    @Inject
+    private AccountService accountService;
+
+    public AccountService getAccountService() {
+        return accountService;
+    }
+
+    public void setAccountService(AccountService accountService) {
+        this.accountService = accountService;
+    }
+
+}

guice/src/main/java/com/baeldung/examples/guice/Person.java

@@ -0,0 +1,39 @@
+package com.baeldung.examples.guice;
+
+import com.baeldung.examples.common.Address;
+import com.google.inject.Inject;
+
+public class Person {
+    private String firstName;
+
+    private String lastName;
+
+    private Address address;
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public void setFirstName(String firstName) {
+        this.firstName = firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public void setLastName(String lastName) {
+        this.lastName = lastName;
+    }
+
+    public Address getAddress() {
+        return address;
+    }
+
+    @Inject
+    public void setAddress(Address address) {
+        this.address = address;
+        address.setCity("Default");
+    }
+
+}

guice/src/main/java/com/baeldung/examples/guice/modules/GuiceModule.java

@@ -0,0 +1,47 @@
+package com.baeldung.examples.guice.modules;
+
+import com.baeldung.examples.common.AccountService;
+import com.baeldung.examples.common.AccountServiceImpl;
+import com.baeldung.examples.common.BookService;
+import com.baeldung.examples.common.BookServiceImpl;
+import com.baeldung.examples.guice.Foo;
+import com.baeldung.examples.guice.Person;
+import com.google.inject.AbstractModule;
+import com.google.inject.Provider;
+import com.google.inject.Provides;
+
+public class GuiceModule extends AbstractModule {
+
+    @Override
+    protected void configure() {
+        try {
+            bind(AccountService.class).to(AccountServiceImpl.class);
+            bind(Foo.class).toProvider(new Provider<Foo>() {
+                public Foo get() {
+                    return null;
+                }
+            });
+
+            bind(Person.class).toConstructor(Person.class.getConstructor());
+            // bind(Person.class).toProvider(new Provider<Person>() {
+            // public Person get() {
+            // Person p = new Person();
+            // return p;
+            // }
+            // });
+        } catch (NoSuchMethodException e) {
+            // TODO Auto-generated catch block
+            e.printStackTrace();
+        } catch (SecurityException e) {
+            // TODO Auto-generated catch block
+            e.printStackTrace();
+        }
+
+    }
+
+    @Provides
+    public BookService bookServiceGenerator() {
+        return new BookServiceImpl();
+    }
+
+}

guice/src/main/java/com/baeldung/examples/spring/AppConfig.java

@@ -0,0 +1,19 @@
+package com.baeldung.examples.spring;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.ComponentScan;
+import org.springframework.context.annotation.Configuration;
+
+import com.baeldung.examples.common.BookService;
+import com.baeldung.examples.common.BookServiceImpl;
+
+@Configuration
+@ComponentScan("com.baeldung.examples")
+public class AppConfig {
+
+    @Bean
+    public BookService bookServiceGenerator() {
+        return new BookServiceImpl();
+    }
+
+}

guice/src/main/java/com/baeldung/examples/spring/SpringUser.java

@@ -0,0 +1,35 @@
+package com.baeldung.examples.spring;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Component;
+
+import com.baeldung.examples.common.Account;
+import com.baeldung.examples.common.Address;
+
+@Component
+public class SpringUser {
+
+    @Autowired
+    private Account account;
+
+    private Address address;
+
+    public Account getAccount() {
+        return account;
+    }
+
+    public void setAccount(Account account) {
+        this.account = account;
+    }
+
+    public Address getAddress() {
+        return address;
+    }
+
+    @Autowired
+    public void setAddress(Address address) {
+        this.address = address;
+        address.setCity("Default");
+    }
+
+}

guice/src/main/java/com/baeldung/examples/spring/Student.java

@@ -0,0 +1,34 @@
+package com.baeldung.examples.spring;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.stereotype.Component;
+
+@Component
+public class Student {
+    private String firstName;
+    private String lastName;
+
+    @Autowired
+    public Student(@Value("Default") String firstName, @Value("Default") String lastName) {
+        this.firstName = firstName;
+        this.lastName = lastName;
+    }
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public void setFirstName(String firstName) {
+        this.firstName = firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public void setLastName(String lastName) {
+        this.lastName = lastName;
+    }
+
+}

guice/src/main/java/com/baeldung/examples/spring/UserService.java

@@ -0,0 +1,22 @@
+package com.baeldung.examples.spring;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Component;
+
+import com.baeldung.examples.common.AccountService;
+
+@Component
+public class UserService {
+
+    @Autowired
+    private AccountService accountService;
+
+    public AccountService getAccountService() {
+        return accountService;
+    }
+
+    public void setAccountService(AccountService accountService) {
+        this.accountService = accountService;
+    }
+
+}

guice/src/test/java/com/baeldung/examples/GuiceTests.java

@@ -0,0 +1,72 @@
+package com.baeldung.examples;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+
+import org.junit.Test;
+
+import com.baeldung.examples.common.BookService;
+import com.baeldung.examples.guice.Employee;
+import com.baeldung.examples.guice.FooGenerator;
+import com.baeldung.examples.guice.GuiceUser;
+import com.baeldung.examples.guice.GuiceUserService;
+import com.baeldung.examples.guice.Person;
+import com.baeldung.examples.guice.modules.GuiceModule;
+import com.google.inject.Guice;
+import com.google.inject.Injector;
+
+public class GuiceTests {
+
+    @Test
+    public void givenAccountFieldInjectedInGuiceUser_WhenGetAccountInvoked_ThenReturnValueIsNotNull() {
+        Injector injector = Guice.createInjector(new GuiceModule());
+        GuiceUser guiceUser = injector.getInstance(GuiceUser.class);
+        assertNotNull(guiceUser.getAccount());
+    }
+
+    @Test
+    public void givenAccountServiceInjectedInGuiceUserService_WhenGetAccountServiceInvoked_ThenReturnValueIsNotNull() {
+        Injector injector = Guice.createInjector(new GuiceModule());
+        GuiceUserService guiceUserService = injector.getInstance(GuiceUserService.class);
+        assertNotNull(guiceUserService.getAccountService());
+    }
+
+    @Test
+    public void givenBookServiceIsRegisteredInModule_WhenBookServiceIsInjected_ThenReturnValueIsNotNull() {
+        Injector injector = Guice.createInjector(new GuiceModule());
+        BookService bookService = injector.getInstance(BookService.class);
+        assertNotNull(bookService);
+    }
+
+    @Test
+    public void givenFooGeneratorConstructorParameterIsNotNullable_WhenFooGeneratorIsInjected_ThenTestFailsByProvisionException() {
+        Injector injector = Guice.createInjector(new GuiceModule());
+        FooGenerator fooGenerator = injector.getInstance(FooGenerator.class);
+        assertNotNull(fooGenerator);
+    }
+
+    @Test
+    public void givenMultipleBindingsForPerson_WhenPersonIsInjected_ThenTestFailsByProvisionException() {
+        Injector injector = Guice.createInjector(new GuiceModule());
+        Person person = injector.getInstance(Person.class);
+        assertNotNull(person);
+    }
+
+    @Test
+    public void givenEmployeeConstructorAnnotatedByInject_WhenEmployeeIsInjected_ThenInstanceWillBeCreatedFromTheConstructor() {
+        Injector injector = Guice.createInjector(new GuiceModule());
+        Employee employee = injector.getInstance(Employee.class);
+        assertNotNull(employee);
+        assertEquals("Default", employee.getLastName());
+    }
+
+    @Test
+    public void givenAddressAutowiredToGuiceUserBySetterInjection_WhenGuiceUserIsInjected_ThenAddressInitializedByTheSetter() {
+        Injector injector = Guice.createInjector(new GuiceModule());
+        GuiceUser guiceUser = injector.getInstance(GuiceUser.class);
+        assertNotNull(guiceUser);
+        assertNotNull(guiceUser.getAddress());
+        assertEquals("Default", guiceUser.getAddress().getCity());
+    }
+
+}

guice/src/test/java/com/baeldung/examples/SpringTests.java

@@ -0,0 +1,58 @@
+package com.baeldung.examples;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.ApplicationContext;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringRunner;
+
+import com.baeldung.examples.common.BookService;
+import com.baeldung.examples.spring.AppConfig;
+import com.baeldung.examples.spring.SpringUser;
+import com.baeldung.examples.spring.Student;
+import com.baeldung.examples.spring.UserService;
+
+@RunWith(SpringRunner.class)
+@ContextConfiguration(classes = { AppConfig.class })
+public class SpringTests {
+    @Autowired
+    ApplicationContext context;
+
+    @Test
+    public void givenAccountFieldAutowiredToSpringUser_WhenGetAccountInvoked_ThenReturnValueIsNotNull() {
+        SpringUser springUser = context.getBean(SpringUser.class);
+        assertNotNull(springUser.getAccount());
+    }
+
+    @Test
+    public void givenAccountServiceFieldAutowiredToUserService_WhenGetAccountServiceInvoked_ThenReturnValueIsNotNull() {
+        UserService userService = context.getBean(UserService.class);
+        assertNotNull(userService.getAccountService());
+    }
+
+    @Test
+    public void givenBookServiceIsRegisteredAsBeanInContext_WhenBookServiceIsRetrievedFromContext_ThenReturnValueIsNotNull() {
+        BookService bookService = context.getBean(BookService.class);
+        assertNotNull(bookService);
+    }
+
+    @Test
+    public void givenStudentConstructorAnnotatedByAutowired_WhenStudentIsRetrievedFromContext_ThenInstanceWillBeCreatedFromTheConstructor() {
+        Student student = context.getBean(Student.class);
+        assertNotNull(student);
+        assertEquals("Default", student.getFirstName());
+        assertEquals("Default", student.getLastName());
+    }
+
+    @Test
+    public void givenAddressAutowiredToSpringUserBySetterInjection_WhenSpringUserRetrievedFromContext_ThenAddressInitializedByTheSetter() {
+        SpringUser springUser = context.getBean(SpringUser.class);
+        assertNotNull(springUser.getAddress());
+        assertEquals("Default", springUser.getAddress().getCity());
+    }
+
+}