blocks|key|1153584|text|实际上，没有一种方法可以直接在VM中完成这项工作，但是您可以通过编程方式在测试机器上设置系统时间。大多数(全部？)操作系统具有执行此操作的命令行命令。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1153585|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

There really isn't a way to do this directly in the VM, but you could all something to programmatically set the system time on the test machine. Most (all?) OS have command line commands to do this.

blocks|key|1368693|text|Powermock运行得很好。只是用它来嘲笑System.currentTimeMillis()。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1368694|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/jayway/powermock^0|M|Q|0|9|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]]|D|@$9|Q|A|R|1|S]]|E|$]]|$1|F|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]]]

<a href="https://github.com/jayway/powermock" rel="nofollow noreferrer">Powermock</a> works great. Just used it to mock <code>System.currentTimeMillis()</code>.

blocks|key|1153694|text|虽然使用一些DateFactory模式似乎很好，但它并没有涵盖您无法控制的库-想象一下依赖于System.currentTimeMillis的实现的验证注解@Past+(确实有这样的库)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1153695|这就是为什么我们使用jmockit直接模拟系统时间的原因：|1153696|import+mockit.Mock;
import+mockit.MockClass;
...
@MockClass(realClass+=+System.class)
public+static+class+SystemMock+{
++++/**
+++++*+Fake+current+time+millis+returns+value+modified+by+required+offset.
+++++*
+++++*+@return+fake+"current"+millis
+++++*/
++++@Mock
++++public+static+long+currentTimeMillis()+{
++++++++return+INIT_MILLIS+%2B+offset+%2B+millisSinceClassInit();
++++}
}

Mockit.setUpMock(SystemMock.class);|code-block|syntax|javascript|1153697|因为不可能得到millis的原始未模拟值，所以我们使用nano+timer代替-这与挂钟无关，但相对时间在这里就足够了：|1153698|//+runs+before+the+mock+is+applied
private+static+final+long+INIT_MILLIS+=+System.currentTimeMillis();
private+static+final+long+INIT_NANOS+=+System.nanoTime();

private+static+long+millisSinceClassInit()+{
++++return+(System.nanoTime()+-+INIT_NANOS)+/+1000000;
}|1153699|有一个记录在案的问题，即在多次调用后，HotSpot的时间恢复正常-这是问题报告：http://code.google.com/p/jmockit/issues/detail?id=43|offset|length|1153700|为了克服这个问题，我们必须开启一个特定的HotSpot优化--使用这个参数-XX:-Inline运行JVM。|style|CODE|1153701|虽然这对于生产来说可能不是完美的，但它对于测试来说是很好的，它对应用程序是绝对透明的，特别是当DataFactory没有商业意义并且仅仅是因为测试而引入的时候。如果有内置的JVM选项可以在不同的时间运行，那就太好了，糟糕的是，如果没有这样的hack，这是不可能的。|1153702|完整的故事在我的博客文章中：http://virgo47.wordpress.com/2012/06/22/changing-system-time-in-java/|1153703|文章中提供了完整的方便的SystemTimeShifter类。类可以在您的测试中使用，或者它可以非常容易地用作真正的主类之前的第一个主类，以便在不同的时间运行您的应用程序(甚至整个appserver)。当然，这主要是为了测试目的，而不是为了生产环境。|1153704|编辑2014年7月:+JMockit最近发生了很大变化，您一定会使用JMockit+1.0来正确使用它。肯定不能升级到界面完全不同的最新版本。我正在考虑只内联必要的东西，但由于我们的新项目中不需要这个东西，所以我根本不开发这个东西。|1153705|entityMap|0|LINK|mutability|MUTABLE|url|http://code.google.com/p/jmockit/issues/detail?id=43|1|http://virgo47.wordpress.com/2012/06/22/changing-system-time-in-java/^0|0|0|0|0|0|15|1G|0|0|11|B|0|0|E|1X|1|0|0|0^^$0|@$1|2|3|4|5|6|7|1C|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1D|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|1E|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|1F|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|1G|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|1H|8|@]|9|@$O|1I|P|1J|1|1K]]|A|$]]|$1|Q|3|R|5|6|7|1L|8|@$O|1M|P|1N|S|T]]|9|@]|A|$]]|$1|U|3|V|5|6|7|1O|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|1P|8|@]|9|@$O|1Q|P|1R|1|1S]]|A|$]]|$1|Y|3|Z|5|6|7|1T|8|@]|9|@]|A|$]]|$1|10|3|11|5|6|7|1U|8|@]|9|@]|A|$]]|$1|12|3|-4|5|6|7|1V|8|@]|9|@]|A|$]]]|13|$14|$5|15|16|17|A|$18|19]]|1A|$5|15|16|17|A|$18|1B]]]]

While using some DateFactory pattern seems nice, it does not cover libraries you can't control - imagine Validation annotation @Past with implementation relying on System.currentTimeMillis (there is such).

That's why we use jmockit to mock the system time directly:

<pre><code>import mockit.Mock;
import mockit.MockClass;
...
@MockClass(realClass = System.class)
public static class SystemMock {
 /**
 * Fake current time millis returns value modified by required offset.
 *
 * @return fake "current" millis
 */
 @Mock
 public static long currentTimeMillis() {
 return INIT_MILLIS + offset + millisSinceClassInit();
 }
}

Mockit.setUpMock(SystemMock.class);
</code></pre>

Because it's not possible to get to the original unmocked value of millis, we use nano timer instead - this is not related to wall clock, but relative time suffices here:

<pre><code>// runs before the mock is applied
private static final long INIT_MILLIS = System.currentTimeMillis();
private static final long INIT_NANOS = System.nanoTime();

private static long millisSinceClassInit() {
 return (System.nanoTime() - INIT_NANOS) / 1000000;
}
</code></pre>

There is documented problem, that with HotSpot the time gets back to normal after a number of calls - here is the issue report: <a href="http://code.google.com/p/jmockit/issues/detail?id=43">http://code.google.com/p/jmockit/issues/detail?id=43</a>

To overcome this we have to turn on one specific HotSpot optimization - run JVM with this argument <code>-XX:-Inline</code>.

While this may not be perfect for production, it is just fine for tests and it is absolutely transparent for application, especially when DataFactory doesn't make business sense and is introduced only because of tests. It would be nice to have built-in JVM option to run in different time, too bad it is not possible without hacks like this.

Complete story is in my blog post here:
<a href="http://virgo47.wordpress.com/2012/06/22/changing-system-time-in-java/">http://virgo47.wordpress.com/2012/06/22/changing-system-time-in-java/</a>

Complete handy class SystemTimeShifter is provided in the post. Class can be used in your tests, or it can be used as the first main class before your real main class very easily in order to run your application (or even whole appserver) in a different time. Of course, this is intented for testing purposes mainly, not for production environment.

EDIT July 2014: JMockit changed a lot lately and you are bound to use JMockit 1.0 to use this correctly (IIRC). Definitely can't upgrade to newest version where interface is completly different. I was thinking about inlining just the necessary stuff, but as we don't need this thing in our new projects I'm not developing this thing at all.

blocks|key|1153730|text|如果你想模拟具有System.currentTimeMillis()参数的方法，那么你可以将Matcher类的anyLong()作为参数传递。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1153731|附注:我可以使用上面的技巧成功地运行我的测试用例，并分享更多关于我使用PowerMock和Mockito框架的测试的详细信息。|1153732|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.mockito.googlecode.com/hg/1.9.5/org/mockito/Matchers.html#anyLong()^0|8|Q|1J|9|1J|9|0|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]|$9|S|A|T|B|C]]|D|@$9|U|A|V|1|W]]|E|$]]|$1|F|3|G|5|6|7|X|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

If you want to mock the method having <code>System.currentTimeMillis()</code> argument then you can pass <a href="http://docs.mockito.googlecode.com/hg/1.9.5/org/mockito/Matchers.html#anyLong()" rel="nofollow"><code>anyLong()</code></a> of Matchers class as an argument.

P.S. I am able to run my test case successfully using the above trick and just to share more details about my test that I am using PowerMock and Mockito frameworks.

blocks|key|1368871|text|一种在Java8Web应用程序中覆盖当前系统时间以进行JUnit测试的有效方法，该应用程序使用EasyMock、没有Joda时间和没有PowerMock。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1368872|下面是你需要做的：|1368873|在测试的类中需要做什么|1368874|第一步|1368875|向经过测试的类MyService添加一个新的java.time.Clock属性，并确保使用实例化块或构造函数将新属性正确地初始化为默认值：|offset|length|style|CODE|1368876|import+java.time.Clock;
import+java.time.LocalDateTime;

public+class+MyService+{
++//+(...)
++private+Clock+clock;
++public+Clock+getClock()+{+return+clock;+}
++public+void+setClock(Clock+newClock)+{+clock+=+newClock;+}

++public+void+initDefaultClock()+{
++++setClock(
++++++Clock.system(
++++++++Clock.systemDefaultZone().getZone()+
++++++++//+You+can+just+as+well+use
++++++++//+java.util.TimeZone.getDefault().toZoneId()+instead
++++++)
++++);
++}
++{+
++++initDefaultClock();+//+initialisation+in+an+instantiation+block,+but+
++++++++++++++++++++++++//+it+can+be+done+in+a+constructor+just+as+well
++}
++//+(...)
}|code-block|syntax|javascript|1368877|第二步|1368878|将新属性clock注入到调用当前日期时间的方法中。例如，在我的例子中，我必须检查存储在数据库中的日期是否发生在LocalDateTime.now()之前，我用LocalDateTime.now(clock)替换了它，如下所示：|1368879|import+java.time.Clock;
import+java.time.LocalDateTime;

public+class+MyService+{
++//+(...)
++protected+void+doExecute()+{
++++LocalDateTime+dateToBeCompared+=+someLogic.whichReturns().aDate().fromDB();
++++while+(dateToBeCompared.isBefore(LocalDateTime.now(clock)))+{
++++++someOtherLogic();
++++}
++}
++//+(...)+
}|1368880|在测试类中需要做什么|1368881|第三步|1368882|在测试类中，创建一个模拟时钟对象，并在调用测试方法doExecute()之前将其注入到被测试类的实例中，然后立即将其重置回来，如下所示：|1368883|import+java.time.Clock;
import+java.time.LocalDateTime;
import+java.time.OffsetDateTime;
import+org.junit.Test;

public+class+MyServiceTest+{
++//+(...)
++private+int+year+=+2017;
++private+int+month+=+2;
++private+int+day+=+3;

++@Test
++public+void+doExecuteTest()+throws+Exception+{
++++//+(...)+EasyMock+stuff+like+mock(..),+expect(..),+replay(..)+and+whatnot

++++MyService+myService+=+new+MyService();
++++Clock+mockClock+=
++++++Clock.fixed(
++++++++LocalDateTime.of(year,+month,+day,+0,+0).toInstant(OffsetDateTime.now().getOffset()),
++++++++Clock.systemDefaultZone().getZone()+//+or+java.util.TimeZone.getDefault().toZoneId()
++++++);
++++myService.setClock(mockClock);+//+set+it+before+calling+the+tested+method

++++myService.doExecute();+//+calling+tested+method+

++++myService.initDefaultClock();+//+reset+the+clock+to+default+right+afterwards+with+our+own+previously+created+method

++++//+(...)+remaining+EasyMock+stuff:+verify(..)+and+assertEquals(..)
++++}
++}|1368884|在调试模式下检查，您会看到2017年2月3日的日期已经正确注入到myService实例中并在比较指令中使用，然后使用initDefaultClock()将其正确重置为当前日期。|1368885|entityMap^0|0|0|0|0|7|9|M|F|0|0|0|4|5|1J|J|27|O|0|0|0|0|P|B|0|0|W|9|1M|I|0^^$0|@$1|2|3|4|5|6|7|1A|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1B|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|1C|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|1D|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|1E|8|@$J|1F|K|1G|L|M]|$J|1H|K|1I|L|M]]|9|@]|A|$]]|$1|N|3|O|5|P|7|1J|8|@]|9|@]|A|$Q|R]]|$1|S|3|T|5|6|7|1K|8|@]|9|@]|A|$]]|$1|U|3|V|5|6|7|1L|8|@$J|1M|K|1N|L|M]|$J|1O|K|1P|L|M]|$J|1Q|K|1R|L|M]]|9|@]|A|$]]|$1|W|3|X|5|P|7|1S|8|@]|9|@]|A|$Q|R]]|$1|Y|3|Z|5|6|7|1T|8|@]|9|@]|A|$]]|$1|10|3|11|5|6|7|1U|8|@]|9|@]|A|$]]|$1|12|3|13|5|6|7|1V|8|@$J|1W|K|1X|L|M]]|9|@]|A|$]]|$1|14|3|15|5|P|7|1Y|8|@]|9|@]|A|$Q|R]]|$1|16|3|17|5|6|7|1Z|8|@$J|20|K|21|L|M]|$J|22|K|23|L|M]]|9|@]|A|$]]|$1|18|3|-4|5|6|7|24|8|@]|9|@]|A|$]]]|19|$]]

<h2>A working way to override current system time for JUnit testing purposes in a Java 8 web application with EasyMock, without Joda Time, and without PowerMock.</h2>

Here's what you need to do:

<h2>What needs to be done in the tested class</h2>

<h3>Step 1</h3>

Add a new <code>java.time.Clock</code> attribute to the tested class <code>MyService</code> and make sure the new attribute will be initialized properly at default values with an instantiation block or a constructor:

<pre><code>import java.time.Clock;
import java.time.LocalDateTime;

public class MyService {
 // (...)
 private Clock clock;
 public Clock getClock() { return clock; }
 public void setClock(Clock newClock) { clock = newClock; }

 public void initDefaultClock() {
 setClock(
 Clock.system(
 Clock.systemDefaultZone().getZone() 
 // You can just as well use
 // java.util.TimeZone.getDefault().toZoneId() instead
 )
 );
 }
 { 
 initDefaultClock(); // initialisation in an instantiation block, but 
 // it can be done in a constructor just as well
 }
 // (...)
}
</code></pre>

<h3>Step 2</h3>

Inject the new attribute <code>clock</code> into the method which calls for a current date-time. For instance, in my case I had to perform a check of whether a date stored in dataase happened before <code>LocalDateTime.now()</code>, which I remplaced with <code>LocalDateTime.now(clock)</code>, like so:

<pre><code>import java.time.Clock;
import java.time.LocalDateTime;

public class MyService {
 // (...)
 protected void doExecute() {
 LocalDateTime dateToBeCompared = someLogic.whichReturns().aDate().fromDB();
 while (dateToBeCompared.isBefore(LocalDateTime.now(clock))) {
 someOtherLogic();
 }
 }
 // (...) 
}
</code></pre>

<h2>What needs to be done in the test class</h2>

<h3>Step 3</h3>

In the test class, create a mock clock object and inject it into the tested class's instance just before you call the tested method <code>doExecute()</code>, then reset it back right afterwards, like so:

<pre><code>import java.time.Clock;
import java.time.LocalDateTime;
import java.time.OffsetDateTime;
import org.junit.Test;

public class MyServiceTest {
 // (...)
 private int year = 2017;
 private int month = 2;
 private int day = 3;

 @Test
 public void doExecuteTest() throws Exception {
 // (...) EasyMock stuff like mock(..), expect(..), replay(..) and whatnot

 MyService myService = new MyService();
 Clock mockClock =
 Clock.fixed(
 LocalDateTime.of(year, month, day, 0, 0).toInstant(OffsetDateTime.now().getOffset()),
 Clock.systemDefaultZone().getZone() // or java.util.TimeZone.getDefault().toZoneId()
 );
 myService.setClock(mockClock); // set it before calling the tested method

 myService.doExecute(); // calling tested method 

 myService.initDefaultClock(); // reset the clock to default right afterwards with our own previously created method

 // (...) remaining EasyMock stuff: verify(..) and assertEquals(..)
 }
 }
</code></pre>

Check it in debug mode and you will see the date of 2017 Feb 3 has been correctly injected into <code>myService</code> instance and used in the comparison instruction, and then has been properly reset to current date with <code>initDefaultClock()</code>.

blocks|key|1153913|text|如果您运行的是Linux，那么可以使用libfaketime的主分支，或者在测试提交4ce2835时使用。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1153914|只需将环境变量设置为您想用来模拟java应用程序的时间，然后使用ld-preloading运行它：|1153915|#+bash
export+FAKETIME="1985-10-26+01:21:00"
export+DONT_FAKE_MONOTONIC=1
LD_PRELOAD=/usr/local/lib/faketime/libfaketimeMT.so.1+java+-jar+myapp.jar|code-block|syntax|javascript|1153916|第二个环境变量对于java应用程序非常重要，否则java应用程序将会冻结。在编写本文时，它需要libfaketime的主分支。|1153917|如果您想更改systemd管理服务的时间，只需将以下内容添加到您的单元文件覆盖中，例如，对于elasticsearch，这将是/etc/systemd/system/elasticsearch.service.d/override.conf|style|CODE|1153918|[Service]
Environment="FAKETIME=2017-10-31+23:00:00"
Environment="DONT_FAKE_MONOTONIC=1"
Environment="LD_PRELOAD=/usr/local/lib/faketime/libfaketimeMT.so.1"|1153919|不要忘记使用`+`systemctl+daemon-reload重新加载systemd|1153920|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/wolfcw/libfaketime/commit/4ce283594fc212d724cf44a90bc3cfc61474b3c9^0|16|7|0|0|0|0|0|1R|1L|0|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@$A|13|B|14|1|15]]|C|$]]|$1|D|3|E|5|6|7|16|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|17|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|18|8|@]|9|@]|C|$]]|$1|M|3|N|5|6|7|19|8|@$A|1A|B|1B|O|P]]|9|@]|C|$]]|$1|Q|3|R|5|H|7|1C|8|@]|9|@]|C|$I|J]]|$1|S|3|T|5|6|7|1D|8|@]|9|@]|C|$]]|$1|U|3|-4|5|6|7|1E|8|@]|9|@]|C|$]]]|V|$W|$5|X|Y|Z|C|$10|11]]]]

If you're running Linux, you can use the master branch of libfaketime, or at the time of testing commit <a href="https://github.com/wolfcw/libfaketime/commit/4ce283594fc212d724cf44a90bc3cfc61474b3c9" rel="nofollow noreferrer">4ce2835</a>.

Simply set the environment variable with the time you'd like to mock your java application with, and run it using ld-preloading:

<pre><code># bash
export FAKETIME="1985-10-26 01:21:00"
export DONT_FAKE_MONOTONIC=1
LD_PRELOAD=/usr/local/lib/faketime/libfaketimeMT.so.1 java -jar myapp.jar
</code></pre>

The second environment variable is paramount for java applications, which otherwise would freeze. It requires the master branch of libfaketime at the time of writing.

If you'd like to change the time of a systemd managed service, just add the following to your unit file overrides, e.g. for elasticsearch this would be <code>/etc/systemd/system/elasticsearch.service.d/override.conf</code>:

<pre><code>[Service]
Environment="FAKETIME=2017-10-31 23:00:00"
Environment="DONT_FAKE_MONOTONIC=1"
Environment="LD_PRELOAD=/usr/local/lib/faketime/libfaketimeMT.so.1"
</code></pre>

Don't forget to reload systemd using `systemctl daemon-reload

blocks|key|1369015|text|下面是一个使用PowerMockito的示例。还有一个使用new+Date()的例子。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1369016|有关mocking+system+classes的更多详细信息。|1369017|@RunWith(PowerMockRunner.class)
@PrepareForTest(LegacyClass.class)
public+class+SystemTimeTest+{
++++
++++private+final+Date+fakeNow+=+Date.from(Instant.parse("2010-12-03T10:15:30.00Z"));

++++@Before
++++public+void+init()+{
++++++++PowerMockito.mockStatic(System.class);
++++++++PowerMockito.when(System.currentTimeMillis()).thenReturn(fakeNow.getTime());
++++++++System.out.println("Fake+currentTimeMillis:+"+%2B+System.currentTimeMillis());
++++}

++++@Test
++++public+void+legacyClass()+{
++++++++new+LegacyClass().methodWithCurrentTimeMillis();
++++}

}|code-block|syntax|javascript|1369018|您正在测试一些遗留类：|1369019|class+LegacyClass+{

++++public+void+methodWithCurrentTimeMillis()+{
++++++++long+now+=+System.currentTimeMillis();
++++++++System.out.println("LegacyClass+System.currentTimeMillis()+is+"+%2B+now);
++++}

}|1369020|控制台输出|1369021|Fake+currentTimeMillis:+1291371330000
LegacyClass+System.currentTimeMillis()+is+1291371330000|1369022|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/66920707/7666239|1|https://github.com/powermock/powermock/wiki/Mock-System^0|T|A|0|0|2|M|1|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@$A|13|B|14|1|15]]|C|$]]|$1|D|3|E|5|6|7|16|8|@]|9|@$A|17|B|18|1|19]]|C|$]]|$1|F|3|G|5|H|7|1A|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|1B|8|@]|9|@]|C|$]]|$1|M|3|N|5|H|7|1C|8|@]|9|@]|C|$I|J]]|$1|O|3|P|5|6|7|1D|8|@]|9|@]|C|$]]|$1|Q|3|R|5|H|7|1E|8|@]|9|@]|C|$I|J]]|$1|S|3|-4|5|6|7|1F|8|@]|9|@]|C|$]]]|T|$U|$5|V|W|X|C|$Y|Z]]|10|$5|V|W|X|C|$Y|11]]]]

Here is an example using PowerMockito. Also there is an example with <a href="https://stackoverflow.com/a/66920707/7666239">new Date()</a>. 
More details about <a href="https://github.com/powermock/powermock/wiki/Mock-System" rel="nofollow noreferrer">mocking system classes</a>.
<pre><code>@RunWith(PowerMockRunner.class)
@PrepareForTest(LegacyClass.class)
public class SystemTimeTest {
 
 private final Date fakeNow = Date.from(Instant.parse(&quot;2010-12-03T10:15:30.00Z&quot;));

 @Before
 public void init() {
 PowerMockito.mockStatic(System.class);
 PowerMockito.when(System.currentTimeMillis()).thenReturn(fakeNow.getTime());
 System.out.println(&quot;Fake currentTimeMillis: &quot; + System.currentTimeMillis());
 }

 @Test
 public void legacyClass() {
 new LegacyClass().methodWithCurrentTimeMillis();
 }

}
</code></pre>
Some legacy class you are testing:
<pre><code>class LegacyClass {

 public void methodWithCurrentTimeMillis() {
 long now = System.currentTimeMillis();
 System.out.println(&quot;LegacyClass System.currentTimeMillis() is &quot; + now);
 }

}
</code></pre>
Console output
<pre><code>Fake currentTimeMillis: 1291371330000
LegacyClass System.currentTimeMillis() is 1291371330000
</code></pre>

Is there a way, either in code or with JVM arguments, to override the current time, as presented via <code>System.currentTimeMillis</code>, other than manually changing the system clock on the host machine?

A little background:

We have a system that runs a number of accounting jobs that revolve much of their logic around the current date (ie 1st of the month, 1st of the year, etc)

Unfortunately, a lot of the legacy code calls functions such as <code>new Date()</code> or <code>Calendar.getInstance()</code>, both of which eventually call down to <code>System.currentTimeMillis</code>.

For testing purposes, right now, we are stuck with manually updating the system clock to manipulate what time and date the code thinks that the test is being run.

So my question is:

Is there a way to override what is returned by <code>System.currentTimeMillis</code>? For example, to tell the JVM to automatically add or subtract some offset before returning from that method?

Thanks in advance!

Override Java System.currentTimeMillis for testing time sensitive code

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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除了手动更改主机上的系统时钟之外，是否有一种方法可以通过代码或使用JVM参数来覆盖通过System.currentTimeMillis呈现的当前时间？下面是一些背景知识：我们有一个系统，它运行许多会计作业，这些作业的大部分逻辑都围绕当前日期(例如，每月1号，每年1号等)不幸的是，许多遗留代码都会调用new Date()...

问覆盖Java System.currentTimeMillis以测试时间敏感的代码
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问覆盖Java System.currentTimeMillis以测试时间敏感的代码EN