Support System Properties as a configuration source (#20)

* Support system properties as a configuration source

Update README

Support system properties as a configuration source

* Rewrite PropertiesConfiguration to use a Map instead of Properties as class variable, refine tests

* Rename variable in PropertiesConfiguration

README.adoc

@@ -14,6 +14,7 @@ CNF-01 is a library that provides immutable configuration for Java projects. Imm
 // List your project's features
 - Provides immutable configurations for:
 . configuration files / path properties (`PathConfiguration`)
+. System Properties (`PropertiesConfiguration`)
 . environment variables (`EnvironmentConfiguration`)
 - Default configurations in case the provided configurations from a source are not found or are otherwise broken (`DefaultConfiguration`)
 

src/main/java/com/teragrep/cnf_01/PropertiesConfiguration.java

@@ -0,0 +1,122 @@
+/*
+ * Teragrep Configuration Library for Java (cnf_01)
+ * Copyright (C) 2024 Suomen Kanuuna Oy
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ *
+ * Additional permission under GNU Affero General Public License version 3
+ * section 7
+ *
+ * If you modify this Program, or any covered work, by linking or combining it
+ * with other code, such other code is not for that reason alone subject to any
+ * of the requirements of the GNU Affero GPL version 3 as long as this Program
+ * is the same Program as licensed from Suomen Kanuuna Oy without any additional
+ * modifications.
+ *
+ * Supplemented terms under GNU Affero General Public License version 3
+ * section 7
+ *
+ * Origin of the software must be attributed to Suomen Kanuuna Oy. Any modified
+ * versions must be marked as "Modified version of" The Program.
+ *
+ * Names of the licensors and authors may not be used for publicity purposes.
+ *
+ * No rights are granted for use of trade names, trademarks, or service marks
+ * which are in The Program if any.
+ *
+ * Licensee must indemnify licensors and authors for any liability that these
+ * contractual assumptions impose on licensors and authors.
+ *
+ * To the extent this program is licensed as part of the Commercial versions of
+ * Teragrep, the applicable Commercial License may apply to this file if you as
+ * a licensee so wish it.
+ */
+package com.teragrep.cnf_01;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.Collections;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Properties;
+import java.util.stream.Collectors;
+
+/**
+ * Provides unmodifiable configuration for Java's Properties object. Uses System properties by default if the
+ * constructor is not given a parameter.
+ */
+public final class PropertiesConfiguration implements Configuration {
+
+    private static final Logger LOGGER = LoggerFactory.getLogger(PropertiesConfiguration.class);
+
+    private final Map<String, String> configuration;
+
+    public PropertiesConfiguration() {
+        this(System.getProperties());
+    }
+
+    public PropertiesConfiguration(final Properties properties) {
+        this(
+                Collections
+                        .unmodifiableMap(
+                                properties
+                                        .entrySet()
+                                        .stream()
+                                        .collect(
+                                                Collectors
+                                                        .toMap(
+                                                                entry -> entry.getKey().toString(),
+                                                                entry -> entry.getValue().toString()
+                                                        )
+                                        )
+                        )
+        );
+    }
+
+    /**
+     * Private constructor so that a map can't be given as parameter by users. It would break immutability.
+     * 
+     * @param configuration the configuration as an immutable Map
+     */
+    private PropertiesConfiguration(final Map<String, String> configuration) {
+        this.configuration = configuration;
+    }
+
+    @Override
+    public Map<String, String> asMap() {
+        LOGGER.debug("Returning configuration map generated from properties.");
+        LOGGER.trace("Returning configuration map <[{}]>", configuration);
+
+        return configuration;
+    }
+
+    @Override
+    public boolean equals(final Object o) {
+        if (this == o) {
+            return true;
+        }
+        else if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        final PropertiesConfiguration config = (PropertiesConfiguration) o;
+        return configuration.equals(config.configuration);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hashCode(configuration);
+    }
+}

src/test/java/com/teragrep/cnf_01/PropertiesConfigurationTest.java

@@ -0,0 +1,158 @@
+/*
+ * Teragrep Configuration Library for Java (cnf_01)
+ * Copyright (C) 2024 Suomen Kanuuna Oy
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ *
+ * Additional permission under GNU Affero General Public License version 3
+ * section 7
+ *
+ * If you modify this Program, or any covered work, by linking or combining it
+ * with other code, such other code is not for that reason alone subject to any
+ * of the requirements of the GNU Affero GPL version 3 as long as this Program
+ * is the same Program as licensed from Suomen Kanuuna Oy without any additional
+ * modifications.
+ *
+ * Supplemented terms under GNU Affero General Public License version 3
+ * section 7
+ *
+ * Origin of the software must be attributed to Suomen Kanuuna Oy. Any modified
+ * versions must be marked as "Modified version of" The Program.
+ *
+ * Names of the licensors and authors may not be used for publicity purposes.
+ *
+ * No rights are granted for use of trade names, trademarks, or service marks
+ * which are in The Program if any.
+ *
+ * Licensee must indemnify licensors and authors for any liability that these
+ * contractual assumptions impose on licensors and authors.
+ *
+ * To the extent this program is licensed as part of the Commercial versions of
+ * Teragrep, the applicable Commercial License may apply to this file if you as
+ * a licensee so wish it.
+ */
+package com.teragrep.cnf_01;
+
+import nl.jqno.equalsverifier.EqualsVerifier;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.Map;
+import java.util.Properties;
+
+public class PropertiesConfigurationTest {
+
+    @Test
+    public void testSystemProperties() {
+        System.setProperty("foo", "bar");
+        System.setProperty("bar", "foo");
+
+        PropertiesConfiguration config = new PropertiesConfiguration(); // uses System.getProperties()
+        // clearing properties doesn't affect PropertiesConfiguration
+        System.clearProperty("foo");
+        System.clearProperty("bar");
+
+        Map<String, String> result = config.asMap();
+
+        Assertions.assertEquals("bar", result.get("foo"));
+        Assertions.assertEquals("foo", result.get("bar"));
+    }
+
+    @Test
+    public void testProperties() {
+        Properties properties = new Properties();
+        properties.put("foo", "bar");
+        properties.put("bar", "foo");
+
+        PropertiesConfiguration config = new PropertiesConfiguration(properties);
+        // modifying the original properties doesn't modify the result map
+        properties.put("biz", "buz");
+
+        Map<String, String> result = config.asMap();
+
+        Assertions.assertEquals(2, result.size());
+        Assertions.assertEquals("bar", result.get("foo"));
+        Assertions.assertEquals("foo", result.get("bar"));
+    }
+
+    @Test
+    public void testEmptyProperties() {
+        Properties properties = new Properties();
+
+        PropertiesConfiguration config = new PropertiesConfiguration(properties);
+        Map<String, String> result = config.asMap();
+
+        Assertions.assertEquals(0, result.size());
+    }
+
+    @Test
+    public void testEqualsWithSystemProperties() {
+        PropertiesConfiguration config1 = new PropertiesConfiguration();
+        PropertiesConfiguration config2 = new PropertiesConfiguration();
+
+        config1.asMap();
+        Assertions.assertEquals(config1, config2);
+    }
+
+    @Test
+    public void testEqualsWithProperties() {
+        Properties properties1 = new Properties();
+        properties1.put("foo", "bar");
+
+        Properties properties2 = new Properties();
+        properties2.put("foo", "bar");
+
+        PropertiesConfiguration config1 = new PropertiesConfiguration(properties1);
+        // modifying properties1 doesn't modify immutable PropertiesConfiguration
+        properties1.put("bar", "foo");
+
+        PropertiesConfiguration config2 = new PropertiesConfiguration(properties2);
+
+        config1.asMap();
+        Assertions.assertEquals(config1, config2);
+    }
+
+    @Test
+    public void testNotEquals() {
+        Properties properties = new Properties();
+        properties.put("foo", "bar");
+
+        PropertiesConfiguration config1 = new PropertiesConfiguration();
+        PropertiesConfiguration config2 = new PropertiesConfiguration(properties);
+
+        Assertions.assertNotEquals(config1, config2);
+    }
+
+    @Test
+    public void testHashCode() {
+        Properties properties1 = new Properties();
+        properties1.put("foo", "bar");
+
+        Properties properties2 = new Properties();
+        properties2.put("foo", "bar");
+
+        PropertiesConfiguration config1 = new PropertiesConfiguration(properties1);
+        PropertiesConfiguration config2 = new PropertiesConfiguration(properties2);
+        PropertiesConfiguration difConfig = new PropertiesConfiguration();
+
+        Assertions.assertEquals(config1.hashCode(), config2.hashCode());
+        Assertions.assertNotEquals(config1.hashCode(), difConfig.hashCode());
+    }
+
+    @Test
+    public void testEqualsVerifier() {
+        EqualsVerifier.forClass(PropertiesConfiguration.class).withNonnullFields("configuration").verify();
+    }
+}