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Merge pull request #19 from avaje/feature/external-config
Use logger.config system property to load external logger configuration
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‎README.md‎

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# avaje-simple-logger
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A SLF4J Logger built primarily for use with GraalVM Native image that writes JSON structured logs to `System.out`.
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It is designed to be used by applications that will be run in **K8s** or **Lambda**.
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A SLF4J Logger built primarily for use with GraalVM Native image that writes JSON structured logs (or plain format)
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to `System.out`. It is designed to be used by applications that will be run in **K8s** or **Lambda**.
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It supports GraalVM Native image, and also supports dynamic log levels. It is built with simple configuration
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in mind based on properties (no reflection).
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## Background
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This logger has been created from the Logback JSON Encoder from [avaje-logback-encoder](https://github.com/avaje/avaje-logback-encoder),
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and turned into a SLF4J Logger, thus removing the dependency on Logback and its associated XML configuration.
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It is not intended to be a full featured logging framework with appenders, filters, etc (sticking to `System.out`).
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## How to use it
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<dependency>
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<groupId>io.avaje</groupId>
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<artifactId>avaje-simple-logger</artifactId>
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<version>1.0</version>
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<version>1.3</version>
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</dependency>
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```
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#log.level.io.ebean.TXN=DEBUG
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```
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## External configuration
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We can override the configuration via setting a system property `logger.config`.
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```sh
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java -Dlogger.config=/path/to/my-logger.properties -jar myapp.jar
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```
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Note that `~` can be used to represent the user home directory like:
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```sh
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java -Dlogger.config=~/my-logger.properties -jar myapp.jar
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```
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When we specify an external configuration file via `logger.config`, then it is used *instead of*
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the default `avaje-logger.properties` and `avaje-logger-test.properties` files.
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## GraalVM Native Image
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When building a GraalVM native image, the *log format* (JSON or plain) is initialised at BUILD time.
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This means that at runtime we cannot change the format via an external configuration file.
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The reason for this, is that GraalVM native image wants to initialize as much as possible at build time,
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and specifically the `System.Logger` is initialised at build time. So as we want avaje-simple-logger to
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be the `System.Logger` implementation, we need to fix the log format at build time.
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## Debugging
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To debug avaje-simple-logger set the log level for `io.avaje.simplelogger` to `DEBUG`

‎avaje-simple-json-logger/src/main/java/io/avaje/simplelogger/encoder/Bootstrap.java‎

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import io.avaje.simplelogger.LoggerContext;
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import org.slf4j.helpers.Reporter;
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import java.io.IOException;
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import java.io.InputStream;
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import java.io.PrintStream;
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import java.io.*;
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import java.time.format.DateTimeFormatter;
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import java.util.*;
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*/
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public final class Bootstrap {
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private static final int LOG_LEVEL_PREFIX_LENGTH = "log.level.".length();
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public static LoggerContext init() {
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Properties properties = loadProperties();
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LogWriter logWriter = createWriter(properties, logFormat(properties));
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String info = properties.getProperty("logger.defaultLogLevel", "info");
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int defaultLevel = SimpleLoggerFactory.stringToLevel(info);
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String defaultLogLevel = properties.getProperty("logger.defaultLogLevel", "info");
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int defaultLevel = SimpleLoggerFactory.stringToLevel(defaultLogLevel);
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String nameLength = properties.getProperty("logger.nameTargetLength", "full");
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Abbreviator abbreviator = Abbreviator.create(nameLength);
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if (key.startsWith("log.level.")) {
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String val = properties.getProperty(key);
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if (val != null) {
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nameLevels.put(key.substring(10), val);
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nameLevels.put(key.substring(LOG_LEVEL_PREFIX_LENGTH), val);
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}
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}
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}
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return Boolean.parseBoolean(Eval.eval(properties.getProperty("logger.showThreadName", "true")));
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}
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private static Properties loadProperties() {
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static Properties loadProperties() {
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String config = System.getProperty("logger.config", System.getenv("LOGGER_CONFIG"));
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if (config != null && !config.isEmpty()) {
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final var properties = loadExternal(config);
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if (isMergeDefaultProperties(properties)) {
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// merge with default properties from avaje-logger.properties
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for (Map.Entry<Object, Object> entry : defaultProperties().entrySet()) {
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properties.putIfAbsent(entry.getKey(), entry.getValue());
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}
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}
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return properties;
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}
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return loadTestProperties(defaultProperties());
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}
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private static boolean isMergeDefaultProperties(Properties properties) {
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return Optional.ofNullable(System.getProperty("logger.config.merge"))
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.or(() -> Optional.ofNullable(System.getenv("LOGGER_CONFIG_MERGE")))
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.or(() -> Optional.ofNullable(properties.getProperty("logger.config.merge")))
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.orElse("true")
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.equalsIgnoreCase("true");
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}
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static Properties defaultProperties() {
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final var properties = new Properties();
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load(properties, "avaje-logger.properties");
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load(properties, "avaje-logger-test.properties");
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loadResource(properties, "avaje-logger.properties");
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return properties;
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}
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static Properties loadTestProperties(Properties properties) {
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loadResource(properties, "avaje-logger-test.properties");
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return properties;
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}
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private static void load(Properties properties, String resourceName) {
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static Properties loadExternal(String fileName) {
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final var properties = new Properties();
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if (fileName.startsWith("~/")) {
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fileName = System.getProperty("user.home") + fileName.substring(1);
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}
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if (loadFile(fileName, properties)) {
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return properties;
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}
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if (!fileName.endsWith(".properties") && loadFile(fileName + ".properties", properties)) {
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return properties;
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}
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Reporter.error("External logger config file not found: " + fileName);
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return properties;
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}
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private static boolean loadFile(String fileName, Properties properties) {
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var file = new File(fileName);
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if (!file.exists()) {
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return false;
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} else {
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loadFileIntoProperties(file, properties);
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return true;
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}
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}
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private static void loadFileIntoProperties(File file, Properties properties) {
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try (var is = new FileInputStream(file)) {
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properties.load(is);
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} catch (IOException e) {
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Reporter.error("Error loading external logger config file: " + file, e);
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}
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}
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private static void loadResource(Properties properties, String resourceName) {
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InputStream is = resource(resourceName);
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if (is != null) {
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try {
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try (is) {
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properties.load(is);
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} catch (IOException e) {
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Reporter.error("Error loading " + resourceName, e);

‎avaje-simple-json-logger/src/test/java/io/avaje/simplelogger/encoder/BootstrapTest.java‎

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package io.avaje.simplelogger.encoder;
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import org.junit.jupiter.api.Test;
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import java.util.Properties;
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import static org.assertj.core.api.Assertions.assertThat;
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class BootstrapTest {
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@Test
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void loadProperties_when_mergeNoClash() {
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System.setProperty("logger.config", "src/test/resources/test-external.properties");
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Properties props = Bootstrap.loadProperties();
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System.clearProperty("logger.config");
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// merged all entries, no clashes
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assertThat(props).hasSize(3);
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assertThat(props.getProperty("log.level.io.banana")).isEqualTo("trace");
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// entries from default properties
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assertThat(props.getProperty("logger.defaultLogLevel")).isEqualTo("debug");
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assertThat(props.getProperty("log.level.io.avaje")).isEqualTo("warn");
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}
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@Test
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void loadProperties_when_merge() {
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System.setProperty("logger.config", "src/test/resources/test-external-merge.properties");
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Properties props = Bootstrap.loadProperties();
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System.clearProperty("logger.config");
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// one merged entry from default avaje-logger.properties
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assertThat(props).hasSize(4);
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assertThat(props.getProperty("log.level.io.apple")).isEqualTo("trace");
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assertThat(props.getProperty("log.level.io.banana")).isEqualTo("trace");
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assertThat(props.getProperty("logger.defaultLogLevel")).isEqualTo("info");
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// entries from default properties
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assertThat(props.getProperty("log.level.io.avaje")).isEqualTo("warn");
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}
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@Test
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void loadProperties_when_override() {
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System.setProperty("logger.config", "src/test/resources/test-external-merge.properties");
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System.setProperty("logger.config.merge", "false");
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Properties props = Bootstrap.loadProperties();
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System.clearProperty("logger.config");
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System.clearProperty("logger.config.merge");
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// no entries from default avaje-logger.properties
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assertThat(props).hasSize(3);
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assertThat(props.getProperty("log.level.io.apple")).isEqualTo("trace");
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assertThat(props.getProperty("log.level.io.banana")).isEqualTo("trace");
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assertThat(props.getProperty("logger.defaultLogLevel")).isEqualTo("info");
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}
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@Test
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void loadExternal() {
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Properties props = Bootstrap.loadExternal("src/test/resources/test-external.properties");
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assertThat(props).hasSize(1);
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String value = props.getProperty("log.level.io.banana");
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assertThat(value).isEqualTo("trace");
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}
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@Test
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void loadExternal_when_missingPropertiesSuffix_expect_addsPropertiesExtension() {
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Properties props = Bootstrap.loadExternal("src/test/resources/test-external");
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assertThat(props).hasSize(1);
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String value = props.getProperty("log.level.io.banana");
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assertThat(value).isEqualTo("trace");
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}
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}

‎avaje-simple-json-logger/src/test/resources/test-external-merge.properties‎

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## Externalized test configuration properties
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logger.defaultLogLevel=info
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log.level.io.apple=trace
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log.level.io.banana=trace

‎avaje-simple-json-logger/src/test/resources/test-external.properties‎

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## Externalized test configuration properties
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log.level.io.banana=trace
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