blocks|key|4526124|text|您可以创建自定义附加器|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4526125|public+class+TestAppender+extends+AppenderBase<LoggingEvent>+{
++++static+List<LoggingEvent>+events+=+new+ArrayList<>();
++++
++++@Override
++++protected+void+append(LoggingEvent+e)+{
++++++++events.add(e);
++++}
}|code-block|syntax|javascript|4526126|并配置logback-test.xml以使用它。现在，我们可以检查测试中的日志记录事件：|4526127|@Test
public+void+test()+{
++++...
++++Assert.assertEquals(1,+TestAppender.events.size());
++++...
}|4526128|注意:如果您没有得到任何输出，请使用ILoggingEvent+-有关原因，请参阅注释部分。|offset|length|style|CODE|4526129|entityMap^0|0|0|0|0|I|D|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@$M|X|N|Y|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

You can create a custom appender
<pre><code>public class TestAppender extends AppenderBase&lt;LoggingEvent&gt; {
 static List&lt;LoggingEvent&gt; events = new ArrayList&lt;&gt;();
 
 @Override
 protected void append(LoggingEvent e) {
 events.add(e);
 }
}
</code></pre>
and configure logback-test.xml to use it. Now we can check logging events from our test:
<pre><code>@Test
public void test() {
 ...
 Assert.assertEquals(1, TestAppender.events.size());
 ...
}
</code></pre>
NOTE: Use <code>ILoggingEvent</code> if you do not get any output - see the comment section for the reasoning.

blocks|key|4526198|text|您可以从http://projects.lidalia.org.uk/slf4j-test/使用slf4j-test。它将整个logback实现替换为用于测试的自己的logback实现，并提供了一个针对日志事件进行断言的slf4j。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4526199|示例：|4526200|<build>
++<plugins>
++++<plugin>
++++++<artifactId>maven-surefire-plugin</artifactId>
++++++<configuration>
++++++++<classpathDependencyExcludes>
++++++++++<classpathDependencyExcludes>ch.qos.logback:logback-classic</classpathDependencyExcludes>
++++++++</classpathDependencyExcludes>
++++++</configuration>
++++</plugin>
++</plugins>
</build>

public+class+Slf4jUser+{

++++private+static+final+Logger+logger+=+LoggerFactory.getLogger(Slf4jUser.class);

++++public+void+aMethodThatLogs()+{
++++++++logger.info("Hello+World!");
++++}
}

public+class+Slf4jUserTest+{

++++Slf4jUser+slf4jUser+=+new+Slf4jUser();
++++TestLogger+logger+=+TestLoggerFactory.getTestLogger(Slf4jUser.class);

++++@Test
++++public+void+aMethodThatLogsLogsAsExpected()+{
++++++++slf4jUser.aMethodThatLogs();

++++++++assertThat(logger.getLoggingEvents(),+is(asList(info("Hello+World!"))));
++++}

++++@After
++++public+void+clearLoggers()+{
++++++++TestLoggerFactory.clear();
++++}
}|code-block|syntax|javascript|4526201|entityMap|0|LINK|mutability|MUTABLE|url|http://projects.lidalia.org.uk/slf4j-test/^0|4|16|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@$A|T|B|U|1|V]]|C|$]]|$1|D|3|E|5|6|7|W|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|X|8|@]|9|@]|C|$I|J]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]]]

You can use slf4j-test from <a href="http://projects.lidalia.org.uk/slf4j-test/" rel="noreferrer">http://projects.lidalia.org.uk/slf4j-test/</a>.
It replaces the entire logback slf4j implementation by it's own slf4j api implementation for tests and provides an api to assert against logging events.

example:

<pre><code>&lt;build&gt;
 &lt;plugins&gt;
 &lt;plugin&gt;
 &lt;artifactId&gt;maven-surefire-plugin&lt;/artifactId&gt;
 &lt;configuration&gt;
 &lt;classpathDependencyExcludes&gt;
 &lt;classpathDependencyExcludes&gt;ch.qos.logback:logback-classic&lt;/classpathDependencyExcludes&gt;
 &lt;/classpathDependencyExcludes&gt;
 &lt;/configuration&gt;
 &lt;/plugin&gt;
 &lt;/plugins&gt;
&lt;/build&gt;

public class Slf4jUser {

 private static final Logger logger = LoggerFactory.getLogger(Slf4jUser.class);

 public void aMethodThatLogs() {
 logger.info("Hello World!");
 }
}

public class Slf4jUserTest {

 Slf4jUser slf4jUser = new Slf4jUser();
 TestLogger logger = TestLoggerFactory.getTestLogger(Slf4jUser.class);

 @Test
 public void aMethodThatLogsLogsAsExpected() {
 slf4jUser.aMethodThatLogs();

 assertThat(logger.getLoggingEvents(), is(asList(info("Hello World!"))));
 }

 @After
 public void clearLoggers() {
 TestLoggerFactory.clear();
 }
}
</code></pre>

blocks|key|18581|text|Logback没有提供这样的方法，但是Slf4j提供了一个简单的解决方案。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|18582|您可以使用ListAppender：一个白盒logback附加器，其中日志条目被添加到public+List字段中，我们可以使用该字段来进行断言。|offset|length|style|CODE|18583|这里有一个简单的例子。|18584|Foo类：|18585|import+org.slf4j.Logger;
import+org.slf4j.LoggerFactory;

public+class+Foo+{

++++static+final+Logger+LOGGER+=+LoggerFactory.getLogger(Foo+.class);

++++public+void+doThat()+{
++++++++logger.info("start");
++++++++//...
++++++++logger.info("finish");
++++}
}|code-block|syntax|javascript|18586|FooTest类：|18587|import+org.slf4j.LoggerFactory;
import+ch.qos.logback.classic.Level;
import+ch.qos.logback.classic.Logger;
import+ch.qos.logback.classic.spi.ILoggingEvent;
import+ch.qos.logback.core.read.ListAppender;

public+class+FooTest+{

++++@Test
++++void+doThat()+throws+Exception+{
++++++++//+get+Logback+Logger+
++++++++Logger+fooLogger+=+(Logger)+LoggerFactory.getLogger(Foo.class);

++++++++//+create+and+start+a+ListAppender
++++++++ListAppender<ILoggingEvent>+listAppender+=+new+ListAppender<>();
++++++++listAppender.start();

++++++++//+add+the+appender+to+the+logger
++++++++fooLogger.addAppender(listAppender);

++++++++//+call+method+under+test
++++++++Foo+foo+=+new+Foo();
++++++++foo.doThat();

++++++++//+JUnit+assertions
++++++++List<ILoggingEvent>+logsList+=+listAppender.list;
++++++++assertEquals("start",+logsList.get(0)
++++++++++++++++++++++++++++++++++++++.getMessage());
++++++++assertEquals(Level.INFO,+logsList.get(0)
+++++++++++++++++++++++++++++++++++++++++.getLevel());

++++++++assertEquals("finish",+logsList.get(1)
+++++++++++++++++++++++++++++++++++++++.getMessage());
++++++++assertEquals(Level.INFO,+logsList.get(1)
+++++++++++++++++++++++++++++++++++++++++.getLevel());
++++}
}|18588|您还可以使用匹配器/断言库作为AssertJ或Hamcrest。|18589|对于AssertJ，它将是：|18590|import+org.assertj.core.api.Assertions;

Assertions.assertThat(listAppender.list)
++++++++++.extracting(ILoggingEvent::getFormattedMessage,+ILoggingEvent::getLevel)
++++++++++.containsExactly(Tuple.tuple("start",+Level.INFO),+Tuple.tuple("finish",+Level.INFO));|18591|entityMap|0|LINK|mutability|MUTABLE|url|https://logback.qos.ch/apidocs/ch/qos/logback/core/read/ListAppender.html^0|0|5|C|17|B|5|C|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|18|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|19|8|@$D|1A|E|1B|F|G]|$D|1C|E|1D|F|G]]|9|@$D|1E|E|1F|1|1G]]|A|$]]|$1|H|3|I|5|6|7|1H|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|1I|8|@]|9|@]|A|$]]|$1|L|3|M|5|N|7|1J|8|@]|9|@]|A|$O|P]]|$1|Q|3|R|5|6|7|1K|8|@]|9|@]|A|$]]|$1|S|3|T|5|N|7|1L|8|@]|9|@]|A|$O|P]]|$1|U|3|V|5|6|7|1M|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|1N|8|@]|9|@]|A|$]]|$1|Y|3|Z|5|N|7|1O|8|@]|9|@]|A|$O|P]]|$1|10|3|-4|5|6|7|1P|8|@]|9|@]|A|$]]]|11|$12|$5|13|14|15|A|$16|17]]]]

The Slf4j API doesn't provide such a way but Logback provides a simple solution.

You can use <a href="https://logback.qos.ch/apidocs/ch/qos/logback/core/read/ListAppender.html" rel="noreferrer"><code>ListAppender</code></a> : a whitebox logback appender where log entries are added in a <code>public List</code> field that we could use to make our assertions. 

Here is a simple example. 

Foo class :

<pre><code>import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class Foo {

 static final Logger LOGGER = LoggerFactory.getLogger(Foo .class);

 public void doThat() {
 logger.info("start");
 //...
 logger.info("finish");
 }
}
</code></pre>

FooTest class :

<pre><code>import org.slf4j.LoggerFactory;
import ch.qos.logback.classic.Level;
import ch.qos.logback.classic.Logger;
import ch.qos.logback.classic.spi.ILoggingEvent;
import ch.qos.logback.core.read.ListAppender;

public class FooTest {

 @Test
 void doThat() throws Exception {
 // get Logback Logger 
 Logger fooLogger = (Logger) LoggerFactory.getLogger(Foo.class);

 // create and start a ListAppender
 ListAppender&lt;ILoggingEvent&gt; listAppender = new ListAppender&lt;&gt;();
 listAppender.start();

 // add the appender to the logger
 fooLogger.addAppender(listAppender);

 // call method under test
 Foo foo = new Foo();
 foo.doThat();

 // JUnit assertions
 List&lt;ILoggingEvent&gt; logsList = listAppender.list;
 assertEquals("start", logsList.get(0)
 .getMessage());
 assertEquals(Level.INFO, logsList.get(0)
 .getLevel());

 assertEquals("finish", logsList.get(1)
 .getMessage());
 assertEquals(Level.INFO, logsList.get(1)
 .getLevel());
 }
}
</code></pre>

You can also use Matcher/assertion libraries as AssertJ or Hamcrest.

With AssertJ it would be : 

<pre><code>import org.assertj.core.api.Assertions;

Assertions.assertThat(listAppender.list)
 .extracting(ILoggingEvent::getFormattedMessage, ILoggingEvent::getLevel)
 .containsExactly(Tuple.tuple("start", Level.INFO), Tuple.tuple("finish", Level.INFO));
</code></pre>

blocks|key|18630|text|尽管创建一个定制的logback附加器是一个很好的解决方案，但这只是第一步，您最终会开发/重新发明slf4j-test，如果您更进一步：spf4j-slf4j-test或其他我还不知道的框架。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|18631|你最终将需要担心你在内存中保存了多少事件，当错误被记录(而不是断言)时单元测试失败，在测试失败时使调试日志可用，等等。|18632|免责声明:我是spf4j-slf4j-test的作者，我写这个后端是为了能够更好地测试spf4j，这是一个很好的地方来查看如何使用spf4j-slf4j-test的例子。我获得的主要优势之一是减少了构建输出(这在Travis中是有限的)，同时仍然拥有失败发生时所需的所有细节。|18633|entityMap|0|LINK|mutability|MUTABLE|url|http://projects.lidalia.org.uk/slf4j-test/|1|http://www.spf4j.org/spf4j-slf4j-test/index.html|2|https://www.spf4j.org/^0|1D|A|0|1W|G|1|0|0|17|5|2|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@$A|U|B|V|1|W]|$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|6|7|10|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|11|8|@]|9|@$A|12|B|13|1|14]]|C|$]]|$1|H|3|-4|5|6|7|15|8|@]|9|@]|C|$]]]|I|$J|$5|K|L|M|C|$N|O]]|P|$5|K|L|M|C|$N|Q]]|R|$5|K|L|M|C|$N|S]]]]

Although creating a custom logback appender is a good solution, it is only the first step, you will eventually end up developing/reinventing <a href="http://projects.lidalia.org.uk/slf4j-test/" rel="noreferrer">slf4j-test</a>, and if you go a bit further: <a href="http://www.spf4j.org/spf4j-slf4j-test/index.html" rel="noreferrer">spf4j-slf4j-test</a> or other frameworks that I don't know of yet.

You will eventually need to worry about how many events you keep in memory, fail unit tests when a error is logged (and not asserted), make debug logs available on test failure, etc...

Disclaimer: I am the author of spf4j-slf4j-test, I wrote this backend to be able to better test <a href="https://www.spf4j.org" rel="noreferrer">spf4j</a>, which is a good place to look at for examples on how to use spf4j-slf4j-test. One of the main advantages I achieved was reducing my build output (which is limited with Travis), while still having all the detail I need when failure happens.

blocks|key|18661|text|一个简单的解决方案可以是用Mockito模拟附加器(例如)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|18662|MyClass.java|18663|@Slf4j
class+MyClass+{
++++public+void+doSomething()+{
++++++++log.info("I'm+on+it!");
++++}
}|code-block|syntax|javascript|18664|MyClassTest.java|18665|import+static+org.hamcrest.MatcherAssert.assertThat;
import+static+org.hamcrest.Matchers.containsString;
import+static+org.hamcrest.Matchers.is;
import+static+org.mockito.Mockito.verify;+++++++++

@RunWith(MockitoJUnitRunner.class)
public+class+MyClassTest+{++++

++++@Mock+private+Appender<ILoggingEvent>+mockAppender;
++++private+MyClass+sut+=+new+MyClass();++++

++++@Before
++++public+void+setUp()+{
++++++++Logger+logger+=+(Logger)+LoggerFactory.getLogger(MyClass.class.getName());
++++++++logger.addAppender(mockAppender);
++++}

++++@Test
++++public+void+shouldLogInCaseOfError()+{
++++++++sut.doSomething();

++++++++verify(mockAppender).doAppend(ArgumentMatchers.argThat(argument+->+{
++++++++++++assertThat(argument.getMessage(),+containsString("I'm+on+it!"));
++++++++++++assertThat(argument.getLevel(),+is(Level.INFO));
++++++++++++return+true;
++++++++}));

++++}

}|18666|注意:我使用断言而不是返回false，因为它使代码和(可能的)错误更容易阅读，但如果您有多个验证，它将不起作用。在这种情况下，您需要返回boolean，以指示该值是否如预期的那样。|offset|length|style|CODE|18667|entityMap^0|0|0|0|0|0|D|5|1W|7|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|X|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|Z|8|@$O|10|P|11|Q|R]|$O|12|P|13|Q|R]]|9|@]|A|$]]|$1|S|3|-4|5|6|7|14|8|@]|9|@]|A|$]]]|T|$]]

A simple solution could be to mock the appender with Mockito (for example)

<h3>MyClass.java</h3>

<pre><code>@Slf4j
class MyClass {
 public void doSomething() {
 log.info("I'm on it!");
 }
}
</code></pre>

<h3>MyClassTest.java</h3>

<pre><code>import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.containsString;
import static org.hamcrest.Matchers.is;
import static org.mockito.Mockito.verify; 

@RunWith(MockitoJUnitRunner.class)
public class MyClassTest { 

 @Mock private Appender&lt;ILoggingEvent&gt; mockAppender;
 private MyClass sut = new MyClass(); 

 @Before
 public void setUp() {
 Logger logger = (Logger) LoggerFactory.getLogger(MyClass.class.getName());
 logger.addAppender(mockAppender);
 }

 @Test
 public void shouldLogInCaseOfError() {
 sut.doSomething();

 verify(mockAppender).doAppend(ArgumentMatchers.argThat(argument -&gt; {
 assertThat(argument.getMessage(), containsString("I'm on it!"));
 assertThat(argument.getLevel(), is(Level.INFO));
 return true;
 }));

 }

}
</code></pre>

NOTE: I'm using assertion rather than returning <code>false</code> as it makes code and (possible) error easier to read, but it won't work if you have multiple verifications. In that case you need to return <code>boolean</code> indicating if the value is as expected.

blocks|key|4526444|text|我推荐一个简单的、可重用的间谍实现，它可以包含在作为JUnit规则的测试中：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4526445|public+final+class+LogSpy+extends+ExternalResource+{

++++private+Logger+logger;
++++private+ListAppender<ILoggingEvent>+appender;

++++@Override
++++protected+void+before()+{
++++++++appender+=+new+ListAppender<>();
++++++++logger+=+(Logger)+LoggerFactory.getLogger(Logger.ROOT_LOGGER_NAME);+//+cast+from+facade+(SLF4J)+to+implementation+class+(logback)
++++++++logger.addAppender(appender);
++++++++appender.start();
++++}

++++@Override
++++protected+void+after()+{
++++++++logger.detachAppender(appender);
++++}

++++public+List<ILoggingEvent>+getEvents()+{
++++++++if+(appender+==+null)+{
++++++++++++throw+new+UnexpectedTestError("LogSpy+needs+to+be+annotated+with+@Rule");
++++++++}
++++++++return+appender.list;
++++}
}|code-block|syntax|javascript|4526446|在您的测试中，您将通过以下方式激活间谍：|4526447|@Rule
public+LogSpy+log+=+new+LogSpy();|4526448|调用log.getEvents()+(或其他自定义方法)来检查记录的事件。|offset|length|style|CODE|4526449|entityMap^0|0|0|0|0|2|F|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@$M|X|N|Y|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

I would recommend a simple, reusable spy implementation that can be included in a test as JUnit rule:

<pre><code>public final class LogSpy extends ExternalResource {

 private Logger logger;
 private ListAppender&lt;ILoggingEvent&gt; appender;

 @Override
 protected void before() {
 appender = new ListAppender&lt;&gt;();
 logger = (Logger) LoggerFactory.getLogger(Logger.ROOT_LOGGER_NAME); // cast from facade (SLF4J) to implementation class (logback)
 logger.addAppender(appender);
 appender.start();
 }

 @Override
 protected void after() {
 logger.detachAppender(appender);
 }

 public List&lt;ILoggingEvent&gt; getEvents() {
 if (appender == null) {
 throw new UnexpectedTestError("LogSpy needs to be annotated with @Rule");
 }
 return appender.list;
 }
}
</code></pre>

In your test, you'd activate the spy in the following way:

<pre><code>@Rule
public LogSpy log = new LogSpy();
</code></pre>

Call <code>log.getEvents()</code> (or other, custom methods) to check the logged events.

blocks|key|4526493|text|使用JUnit5+%2B+AssertJ|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4526494|private+ListAppender<ILoggingEvent>+logWatcher;

@BeforeEach
void+setup()+{
++this.logWatcher+=+new+ListAppender<>();
++this.logWatcher.start();
++((Logger)+LoggerFactory.getLogger(MyClass.class)).addAppender(this.logWatcher);
}


@Test
void+myMethod_logs2Messages()+{

++...
++int+logSize+=+logWatcher.list.size();
++assertThat(logWatcher.list.get(logSize+-+2).getFormattedMessage()).contains("EXPECTED+MSG+1");
++assertThat(logWatcher.list.get(logSize+-+1).getFormattedMessage()).contains("EXPECTED+MSG+2");
}|code-block|syntax|javascript|4526495|4526496|归功于：@davidxxx的答案。查看import+ch.qos.logback...详细信息：https://stackoverflow.com/a/52229629/601844|offset|length|style|CODE|4526497|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/52229629/601844^0|0|0|0|J|O|1C|17|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|W|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|X|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|Y|8|@$J|Z|K|10|L|M]]|9|@$J|11|K|12|1|13]]|A|$]]|$1|N|3|-4|5|6|7|14|8|@]|9|@]|A|$]]]|O|$P|$5|Q|R|S|A|$T|U]]]]

<h1>With JUnit5 + AssertJ</h1>
<pre><code>private ListAppender&lt;ILoggingEvent&gt; logWatcher;

@BeforeEach
void setup() {
 this.logWatcher = new ListAppender&lt;&gt;();
 this.logWatcher.start();
 ((Logger) LoggerFactory.getLogger(MyClass.class)).addAppender(this.logWatcher);
}


@Test
void myMethod_logs2Messages() {

 ...
 int logSize = logWatcher.list.size();
 assertThat(logWatcher.list.get(logSize - 2).getFormattedMessage()).contains(&quot;EXPECTED MSG 1&quot;);
 assertThat(logWatcher.list.get(logSize - 1).getFormattedMessage()).contains(&quot;EXPECTED MSG 2&quot;);
}
</code></pre>
<hr />
credits to: @davidxxx's answer. See it for <code>import ch.qos.logback...</code> details: <a href="https://stackoverflow.com/a/52229629/601844">https://stackoverflow.com/a/52229629/601844</a>

Is it possible to somehow intercept the logging (SLF4J + logback) and get an <code>InputStream</code> (or something else that is readable) via a JUnit test case...?

How to intercept SLF4J (with logback) logging via a JUnit test?

单元测试

有没有可能以某种方式截取日志记录(SLF4J + logback)，并通过JUnit测试用例获得InputStream (或其他可读内容)...？

问如何通过JUnit测试拦截SLF4J (带logback)日志？
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