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Log4j 2 asserting log entries with Junit

Log4j 2 asserting log entries with Junit

Lets start with the usage in JUnit

@Rule public LogAccessor logAccessor=new LogAccessor();

@Test @LogAccessorLogLevel(level = "DEBUG", category = "com.cedricwalter")
public void act_arrange_assert() {
    // Arrange          
    // Act           
    // Assert      
    logAccessor.assertCount(1).assertLevel(Level.DEBUG).assertMessage("Hellow World");
}

Notes
LogAccessorLogLevel is optionnal

Define a new annotation LogAccessorLogLevel .java:

package com.cedricwalter.logging;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(value = RetentionPolicy.RUNTIME)
@Target(value = {ElementType.METHOD})
public @interface LogAccessorLogLevel {
    String level() default "ERROR";

    String category() default "";
}

Create a new appender TestAppender.java

package com.cedricwalter.logging;

import org.apache.logging.log4j.core.Filter;
import org.apache.logging.log4j.core.Layout;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.appender.AbstractAppender;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;

public class TestAppender extends AbstractAppender {
    private final List log = new ArrayList<>();

    protected TestAppender(String name, Filter filter, Layout<? extends Serializable> layout) {
        super(name, filter, layout);
    }

    public List getLog() {
        return new ArrayList<>(log);
    }

    @Override
    public void append(LogEvent logEvent) {
        log.add(logEvent);
    }
}

add the Rule class

package com.cedricwalter.logging;

import org.apache.logging.log4j.Level;
import org.junit.rules.TestWatcher;
import org.junit.runner.Description;

import java.util.List;

import static com.innoveo.skye.common.utils.matcher.RegexMatcher.matches;
import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.is;

public class LogAccessor extends TestWatcher {
    private TestAppender appender;
    private LogAccessorLogLevel logAccessorLogLevel;

    private List getLog() {
        return getAppender().getLog();
    }

    public LogAccessor assertCount(int expectedLogEntryCount) {
        assertThat(getLog().size(), is(expectedLogEntryCount));
        return this;
    }

    public LogAccessor assertLevel(Level expectErrorLevel) {
        assertThat(getLog().get(0).getLevel(), is(expectErrorLevel));
        return this;
    }

    public LogAccessor assertMessage(String expectedMessage) {
        assertThat(getLog().get(0).getMessage().getFormattedMessage(), matches(expectedMessage));
        return this;
    }

    @Override
    protected void starting(Description description) {
        appender = new TestAppender("testAppender", null, null);
        Level level = getLevel(description);          /
        /Add appender to root logger
        org.apache.logging.log4j.core.Logger rootLogger = (org.apache.logging.log4j.core.Logger) LogManager.getRootLogger();
        Configuration configuration = rootLogger.getContext().getConfiguration();
        configuration.addLoggerAppender(rootLogger, appender);
        String logCategory = getLogCategory(description);
        if (logCategory != null) {
            changeLoggerLevel(logCategory, level, appender);
        }
    }

    /**
     * The problem was with the getLoggerConfig() call;
     * if the module you are trying to give a new level is not yet
     * * registered, this method returns the root logger (or any intermediate sub path registered), and thus instead
     * * of altering the level for com.mycompany you will alter root or com level. That's why you have to add a new
     * * LoggerConfig in case the module to alter is not yet registered.
     * *
     * * @param module
     * * @param level      * @param appender
     */
    private static void changeLoggerLevel(final String module, final Level level, TestAppender appender) {
        LoggerContext ctx = (LoggerContext) LogManager.getContext(false);
        AbstractConfiguration configuration = (AbstractConfiguration) ctx.getConfiguration();
        LoggerConfig loggerConfig = configuration.getLogger(module);
        if (loggerConfig != null) {
            org.apache.logging.log4j.core.Logger logger = (org.apache.logging.log4j.core.Logger) LogManager.getLogger(module);
            configuration.addLoggerAppender(logger, appender);
            loggerConfig.setLevel(level);
        } else {
            loggerConfig = new LoggerConfig(module, level, true);
            configuration.addLogger(module, loggerConfig);
            ctx.updateLoggers(configuration);
            org.apache.logging.log4j.core.Logger logger = (org.apache.logging.log4j.core.Logger) LogManager.getLogger(module);
            configuration.addLoggerAppender(logger, appender);
            loggerConfig.setLevel(level);
        }
        ctx.updateLoggers(configuration);
    }

    @Override
    protected void finished(Description description) {
        removeAppender(LogManager.ROOT_LOGGER_NAME);
        String logCategory = getLogCategory(description);
        if (logCategory != null) {
            removeAppender(logCategory);
        }
    }

    private void removeAppender(String loggerName) {
        org.apache.logging.log4j.core.Logger logger = (org.apache.logging.log4j.core.Logger) LogManager.getLogger(loggerName);
        Configuration configuration = logger.getContext().getConfiguration();
        LoggerConfig loggerConfig = configuration.getLoggerConfig(loggerName);
        loggerConfig.removeAppender(appender.getName());
    }

    private TestAppender getAppender() {
        return appender;
    }

    private Level getLevel(Description description) {
        logAccessorLogLevel = description.getAnnotation(LogAccessorLogLevel.class);
        if (logAccessorLogLevel != null) {
            return Level.toLevel(logAccessorLogLevel.level());
        }
        return Level.ERROR;
    }

    private String getLogCategory(Description description) {
        logAccessorLogLevel = description.getAnnotation(LogAccessorLogLevel.class);
        if (logAccessorLogLevel != null) {
            return logAccessorLogLevel.category().getLoggerName();
        }
        return null;
    }

    @Override
    public String toString() {
        LoggerContext ctx = (LoggerContext) LogManager.getContext(false);
        StringBuilder str = new StringBuilder();
        for (LoggerConfig logger : ctx.getConfiguration().getLoggers().values()) {
            final String loggerName = LogManager.ROOT_LOGGER_NAME.equals(logger.getName()) ? "Root Logger" : logger.getName();
            str.append("Found logger '" + loggerName + "' with level " + logger.getLevel());
        }
        return str.toString();
    }
}

About The Author

Cédric Walter

I worked with various Insurances companies across Switzerland on online applications handling billion premium volumes. I love to continuously spark my creativity in many different and challenging open-source projects fueled by my great passion for innovation and blockchain technology. In my technical role as a senior software engineer and Blockchain consultant, I help to define and implement innovative solutions in the scope of both blockchain and traditional products, solutions, and services. I can support the full spectrum of software development activities, starting from analyzing ideas and business cases and up to the production deployment of the solutions. I'm the Founder and CEO of Disruptr GmbH.

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