code manipulation : reflection(간단한 DI 프레임워크 만들기)

code-manipulation/di-example/pom.xml

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+<?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>
+
+  <groupId>org.example</groupId>
+  <artifactId>di-example</artifactId>
+  <version>1.0-SNAPSHOT</version>
+
+  <name>di-example</name>
+  <!-- FIXME change it to the project's website -->
+  <url>http://www.example.com</url>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <maven.compiler.source>11</maven.compiler.source>
+    <maven.compiler.target>11</maven.compiler.target>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>4.11</version>
+      <scope>test</scope>
+    </dependency>
+
+    <dependency>
+      <groupId>org.example</groupId>
+      <artifactId>reflection-example</artifactId>
+      <version>1.0-SNAPSHOT</version>
+    </dependency>
+  </dependencies>
+
+</project>

code-manipulation/di-example/src/main/java/org/example/AccountRepository.java

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+package org.example;
+
+public class AccountRepository {
+
+    public void save() {
+        System.out.println("Repo.save()");
+    }
+}

code-manipulation/di-example/src/main/java/org/example/AccountService.java

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+package org.example;
+
+import org.example.di.Inject;
+
+public class AccountService {
+
+    @Inject
+    AccountRepository accountRepository;
+
+    public void join() {
+        System.out.println("Service.join()");
+        accountRepository.save();
+    }
+}

code-manipulation/di-example/src/main/java/org/example/App.java

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+package org.example;
+
+import org.example.di.ContainerService;
+
+/**
+ * Hello world!
+ *
+ */
+public class App {
+    public static void main( String[] args ) {
+
+        AccountService accountService = ContainerService.getObject(AccountService.class);
+        accountService.join();
+    }
+}

code-manipulation/di-example/src/test/java/org/example/AppTest.java

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+package org.example;
+
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+/**
+ * Unit test for simple App.
+ */
+public class AppTest 
+{
+    /**
+     * Rigorous Test :-)
+     */
+    @Test
+    public void shouldAnswerWithTrue()
+    {
+        assertTrue( true );
+    }
+}

code-manipulation/reflection-example/src/main/java/org/example/di/ContainerService.java

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+package org.example.di;
+
+import java.util.Arrays;
+
+public class ContainerService {
+
+    public static <T> T getObject(Class<T> classType) {
+        T instance = createInstance(classType);
+        Arrays.stream(classType.getDeclaredFields()).forEach(field -> {
+            if (field.getAnnotation(Inject.class) != null) {
+                Object fieldInstance = createInstance(field.getType());
+                field.setAccessible(true);
+                try {
+                    field.set(instance, fieldInstance);
+                } catch (IllegalAccessException e) {
+                    throw new RuntimeException();
+                }
+            }
+        });
+        return instance;
+    }
+
+    private static <T> T createInstance(Class<T> classType)  {
+        try {
+            return classType.getConstructor().newInstance();
+        } catch (Exception e) {
+            throw new RuntimeException(e);
+        }
+    }
+}

code-manipulation/reflection-example/src/main/java/org/example/di/Inject.java

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+package org.example.di;
+
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+@Retention(RetentionPolicy.RUNTIME)
+public @interface Inject {
+}

code-manipulation/reflection-example/src/test/java/org/example/di/BookRepository.java

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+package org.example.di;
+
+public class BookRepository {
+}

code-manipulation/reflection-example/src/test/java/org/example/di/BookService.java

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+package org.example.di;
+
+public class BookService {
+
+    @Inject
+    BookRepository bookRepository;
+}

code-manipulation/reflection-example/src/test/java/org/example/di/ContainerServiceTest.java

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+package org.example.di;
+
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class ContainerServiceTest {
+
+    @Test
+    public void getObject_BookRepository() {
+        BookRepository bookRepository = ContainerService.getObject(BookRepository.class);
+        assertNotNull(bookRepository);
+    }
+
+    @Test
+    public void getObject_BookService() {
+        BookService bookService = ContainerService.getObject(BookService.class);
+        assertNotNull(bookService);
+        assertNotNull(bookService.bookRepository);
+    }
+}