JMeter-使用 ${} 或 vars.get() 获取变量值有什么区别

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问题描述

今天调试JMeter脚本的时候，发现了一个让我很困惑的问题.

Today when I was debugging my JMeter script, I found a problem that confused me a lot.

CSV 数据配置元素:在 CSV 中，我将变量 userId 设置为 1001200

然后运行下面的脚本，在使用${userId}和vars.get("userId")时得到不同的userId"值.我认为它们应该是相同的值，但似乎不是.运行后 vars.put("userId", "-111"), ${userId} 和 vars.get("userId")获得不同的值:

Then run script below, and get different value of "userId" when using ${userId} and vars.get("userId"). I think they should be same value, but it seems not. After run vars.put("userId", "-111"), ${userId} and vars.get("userId") get different values:

所以看起来 ${} 和 vars.get() 有一些不同，即使它们的变量是相同的，有人知道原因吗?

so it seems ${} and vars.get() have some difference even though their variable is same, does anyone know the reason?

提前致谢.

推荐答案

@user7294900 提供的答案是指选中缓存编译脚本选项的情况.但即使没有检查，您的脚本也会解析定义为 ${varName} before 执行的变量，而 vars.get("varName") 在执行过程中解决.

Answer provided by @user7294900 refers to the case when Cache compiled script option is checked. But even if it's not checked, your script will resolve variables defined as ${varName} before execution, while vars.get("varName") is resolved during execution.

在 JMeter 即将运行任何元素(采样器、预处理器或后处理器)之前，它将获取(每个)文本字段并解析任何变量、函数或内联代码，由 ${...} 到评估时可用的值.因此语法 ${...} 将变量转换为常量字符串，您的代码(对于 Groovy 或任何其他执行引擎)将如下所示:

Before JMeter is about to run any element (sampler, pre- or post-processor), it will take (every) text field and will resolve any variables, functions or inline code, identified by ${...} to their values available at the time of the evaluation. Thus syntax ${...} converts variable into a constant string and your code (for Groovy or any other execution engine) will look like this:

    log.info("***" + "1001200" + "***");
    log.info("***" + vars.get("userId") + "***");
    vars.put("userId", "-111");
    log.info("***" + "1001200" + "***");
    log.info("***" + vars.get("userId") + "***");

因此无论您在执行过程中如何更改变量，它都不会更改，因为它不再是变量.但另一方面，vars.get("userId") 是一个函数调用，每次都会检查变量值.

Thus no matter how you change variable during execution, it won't change since it's no longer a variable. But vars.get("userId") on the other hand, is a function call and will check variable value every single time.

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