Adds DI and SPI examples

di/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://maven.apache.org/POM/4.0.0"
+         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>
+    <parent>
+        <groupId>fr.gasser</groupId>
+        <artifactId>java-cookbook</artifactId>
+        <version>1.0-SNAPSHOT</version>
+    </parent>
+    <artifactId>di</artifactId>
+</project>

di/src/main/java/ovh/gasser/di/InjectConstant.java

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+package ovh.gasser.di;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ ElementType.FIELD })
+public @interface InjectConstant {
+}

di/src/main/java/ovh/gasser/di/InjectionUtils.java

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+package ovh.gasser.di;
+
+import java.util.Arrays;
+import java.util.Map;
+
+public interface InjectionUtils {
+    static void populateConstants(Class<?> clazz, Map<?, ?> values) {
+        Arrays.stream(clazz.getDeclaredFields())
+                .filter(field -> field.isAnnotationPresent(InjectConstant.class))
+                .forEach(field -> {
+                    try {
+                        field.set(null, values.get(field.getName()));
+                    } catch (IllegalAccessException e) {
+                        throw new RuntimeException("Unable to setup constant for field " + field.getName(), e);
+                    }
+                });
+    }
+}

di/src/main/java/ovh/gasser/di/TestClass.java

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+package ovh.gasser.di;
+
+import java.util.Map;
+
+public class TestClass {
+    @InjectConstant
+    public static String TEST;
+
+    static {
+        Map<String, String> values = Map.of("TEST", "Injected value for TEST");
+        InjectionUtils.populateConstants(TestClass.class, values);
+    }
+
+    public static void main(String[] args) {
+        System.out.println(TEST);
+    }
+}

di/src/main/java/ovh/gasser/translation/InjectTranslation.java

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+package ovh.gasser.translation;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ ElementType.FIELD })
+public @interface InjectTranslation {
+}

di/src/main/java/ovh/gasser/translation/InjectionUtils.java

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+package ovh.gasser.translation;
+
+import org.w3c.dom.Document;
+
+import javax.xml.parsers.DocumentBuilder;
+import javax.xml.parsers.DocumentBuilderFactory;
+import javax.xml.xpath.*;
+import java.util.Arrays;
+
+final class InjectionUtils {
+    private static final XPath xPath;
+    private static final Document document;
+
+    static {
+        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
+        try {
+            var resource = InjectionUtils.class.getResource("/translations.xml");
+            DocumentBuilder documentBuilder = dbf.newDocumentBuilder();
+            document = documentBuilder.parse(resource.getFile());
+            XPathFactory xpf = XPathFactory.newInstance();
+            xPath = xpf.newXPath();
+        } catch (Exception e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    /**
+     * Private ctor to prevent instantiation
+     */
+    private InjectionUtils() {
+        throw new IllegalStateException();
+    }
+
+    static void populateTranslations(Class<?> clazz, String language) {
+        Arrays.stream(clazz.getDeclaredFields())
+                .filter(field -> field.isAnnotationPresent(InjectTranslation.class))
+                .forEach(field -> {
+                    try {
+                        String expression = String.format("/translations/string[@key='%s']/translation[@lang='%s']", field.getName(), language);
+                        XPathExpression xPathExpression = xPath.compile(expression);
+                        String s = (String) xPathExpression.evaluate(document, XPathConstants.STRING);
+                        field.set(null, s);
+                    } catch (IllegalAccessException e) {
+                        throw new RuntimeException("Unable to setup constant for field " + field.getName(), e);
+                    } catch (XPathExpressionException e) {
+                        throw new RuntimeException(e);
+                    }
+                });
+    }
+}

di/src/main/java/ovh/gasser/translation/Main.java

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+package ovh.gasser.translation;
+
+public class Main {
+    public static void main(String[] args) {
+        InjectionUtils.populateTranslations(TestClass.class, "DE");
+        System.out.println(TestClass.HELLO);
+    }
+
+    private static class TestClass {
+        @InjectTranslation
+        static String HELLO;
+    }
+}

di/src/main/resources/translations.xml

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+<?xml version="1.0" encoding="utf-8" ?>
+<translations>
+    <string key="HELLO">
+        <translation lang="EN">Hello</translation>
+        <translation lang="FR">Bonjour</translation>
+        <translation lang="DE">Guten tag</translation>
+    </string>
+</translations>