Java 基于 ByteBuddy 重写系统当前时间

文章目录

• 一般单元测试时总会有些代码会严重依赖系统当前时间，这种情况下的测试代码写起来可能就比较费劲，此处分享一种基于 ByteBuddy 的覆盖 System.currentTimeMillis 的解决方案。
• ByteBuddy 是啥以及作用等详细介绍可以参照官网，此处直接上代码了： <dependency> <groupId>net.bytebuddy</groupId> <artifactId>byte-buddy</artifactId> <version>1.8.22</version> <scope>test</scope> </dependency> <dependency> <groupId>net.bytebuddy</groupId> <artifactId>byte-buddy-agent</artifactId> <version>1.8.22</version> <scope>test</scope> </dependency>
• 此处有两个注意点，一是系统方法被覆盖后咱们也拿不到当前时间了，这个问题基于 nanoTime 做一下手动计时，二是 classloader 的限制会拿不到成员变量，通过反射绕了一下 public static class SystemAdvice { public static long startMill; public static long startNano; public static long offset; @Advice.OnMethodExit public static void currentTimeMillis(@Advice.Return(readOnly = false) long x) { try { Class<?> clazz = Thread.currentThread().getContextClassLoader().loadClass("com.*****$SystemAdvice"); x = clazz.getField("startMill").getLong(null) + (System.nanoTime() - clazz.getField("startNano").getLong(null)) / 1000000 + clazz.getField("offset").getLong(null); } catch (Throwable e) { e.printStackTrace(); } } }
• public static void resetTimeTo(Date date) { AgentBuilder a = new AgentBuilder.Default() .enableNativeMethodPrefix("wmsnative") .with(new ByteBuddy().with(Implementation.Context.Disabled.Factory.INSTANCE)) .with(AgentBuilder.InitializationStrategy.NoOp.INSTANCE) .with(AgentBuilder.RedefinitionStrategy.REDEFINITION) .with(AgentBuilder.TypeStrategy.Default.REDEFINE) .ignore(ElementMatchers.none()) .type(ElementMatchers.named("java.lang.System")) .transform((builder, typeDescription, classLoader, module) -> { return builder.method(ElementMatchers.named("currentTimeMillis")) .intercept( Advice.to(SystemAdvice.class).wrap(StubMethod.INSTANCE) ); }); Instrumentation inst = ByteBuddyAgent.install(); SystemAdvice.startMill = System.currentTimeMillis(); SystemAdvice.startNano = System.nanoTime(); a.installOn(inst); SystemAdvice.offset = date.getTime() - SystemAdvice.startMill; }
• 简单执行一下测试代码： SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); resetTimeTo(sdf.parse("2021-11-11 23:23:23")); for(int i = 0; i < 10; i ++) { System.out.println(sdf.format(new Date())); Thread.sleep(1000); } 得到有序打印的时间序列： 2021-11-11 23:23:23 2021-11-11 23:23:24 2021-11-11 23:23:25 2021-11-11 23:23:26 2021-11-11 23:23:27 2021-11-11 23:23:28 2021-11-11 23:23:29 2021-11-11 23:23:30 2021-11-11 23:23:31 2021-11-11 23:23:32

一般单元测试时总会有些代码会严重依赖系统当前时间，这种情况下的测试代码写起来可能就比较费劲，此处分享一种基于 ByteBuddy 的覆盖 System.currentTimeMillis 的解决方案。

ByteBuddy 是啥以及作用等详细介绍可以参照官网，此处直接上代码了：

<dependency>
    <groupId>net.bytebuddy</groupId>
    <artifactId>byte-buddy</artifactId>
    <version>1.8.22</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>net.bytebuddy</groupId>
    <artifactId>byte-buddy-agent</artifactId>
    <version>1.8.22</version>
    <scope>test</scope>
</dependency>

此处有两个注意点，一是系统方法被覆盖后咱们也拿不到当前时间了，这个问题基于 nanoTime 做一下手动计时，二是 classloader 的限制会拿不到成员变量，通过反射绕了一下

public static class SystemAdvice {

    public static long startMill;
    public static long startNano;
    public static long offset;

    @Advice.OnMethodExit
    public static void currentTimeMillis(@Advice.Return(readOnly = false) long x) {
        try {
            Class<?> clazz = Thread.currentThread().getContextClassLoader().loadClass("com.*****$SystemAdvice");
            x = clazz.getField("startMill").getLong(null)
                    + (System.nanoTime() - clazz.getField("startNano").getLong(null)) / 1000000
                    + clazz.getField("offset").getLong(null);
        } catch (Throwable e) {
            e.printStackTrace();
        }

    }
}

public static void resetTimeTo(Date date) {
    AgentBuilder a = new AgentBuilder.Default()
            .enableNativeMethodPrefix("wmsnative")
            .with(new ByteBuddy().with(Implementation.Context.Disabled.Factory.INSTANCE))
            .with(AgentBuilder.InitializationStrategy.NoOp.INSTANCE)
            .with(AgentBuilder.RedefinitionStrategy.REDEFINITION)
            .with(AgentBuilder.TypeStrategy.Default.REDEFINE)
            .ignore(ElementMatchers.none())
            .type(ElementMatchers.named("java.lang.System"))
            .transform((builder, typeDescription, classLoader, module) -> {
                return builder.method(ElementMatchers.named("currentTimeMillis"))
                        .intercept(
                                Advice.to(SystemAdvice.class).wrap(StubMethod.INSTANCE)
                        );
            });
    Instrumentation inst = ByteBuddyAgent.install();
    SystemAdvice.startMill = System.currentTimeMillis();
    SystemAdvice.startNano = System.nanoTime();
    a.installOn(inst);

    SystemAdvice.offset = date.getTime() - SystemAdvice.startMill;
}

简单执行一下测试代码：

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
resetTimeTo(sdf.parse("2021-11-11 23:23:23"));
for(int i = 0; i < 10; i ++) {
    System.out.println(sdf.format(new Date()));
    Thread.sleep(1000);
}

得到有序打印的时间序列：

2021-11-11 23:23:23
2021-11-11 23:23:24
2021-11-11 23:23:25
2021-11-11 23:23:26
2021-11-11 23:23:27
2021-11-11 23:23:28
2021-11-11 23:23:29
2021-11-11 23:23:30
2021-11-11 23:23:31
2021-11-11 23:23:32