JMeter跨JSR223 Sampler传递自定义对象遇类型转换异常

问题现象 #

在JMeter 5.6.3中使用Groovy 3.0.20的JSR223采样器，将自定义TestDataModel对象列表通过vars.putObject()存入JMeter变量，同一采样器内读取操作正常，但跨采样器用vars.getObject()读取后遍历，抛出类型转换异常：

message: javax.script.ScriptException: org.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object 'TestDataModel@5b28818c' with class 'TestDataModel' to class 'TestDataModel'
javax.script.ScriptException: org.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object 'TestDataModel@5b28818c' with class 'TestDataModel' to class 'TestDataModel'
    at org.codehaus.groovy.jsr223.GroovyScriptEngineImpl.eval(GroovyScriptEngineImpl.java:320) ~[groovy-jsr223-3.0.20.jar:3.0.20]
    at org.codehaus.groovy.jsr223.GroovyCompiledScript.eval(GroovyCompiledScript.java:71) ~[groovy-jsr223-3.0.20.jar:3.0.20]
    at java.scripting/javax.script.CompiledScript.eval(CompiledScript.java:89) ~[java.scripting:?]
    at org.apache.jmeter.util.JSR223TestElement.processFileOrScript(JSR223TestElement.java:230) ~[ApacheJMeter_core.jar:5.6.3]
    at org.apache.jmeter.protocol.java.sampler.JSR223Sampler.sample(JSR223Sampler.java:72) [ApacheJMeter_java.jar:5.6.3]
    at org.apache.jmeter.threads.JMeterThread.doSampling(JMeterThread.java:651) [ApacheJMeter_core.jar:5.6.3]
    at org.apache.jmeter.threads.JMeterThread.executeSamplePackage(JMeterThread.java:570) [ApacheJMeter_core.jar:5.6.3]
    at org.apache.jmeter.threads.JMeterThread.processSampler(JMeterThread.java:501) [ApacheJMeter_core.jar:5.6.3]
    at org.apache.jmeter.threads.JMeterThread.run(JMeterThread.java:268) [ApacheJMeter_core.jar:5.6.3]
    at java.base/java.lang.Thread.run(Thread.java:834) [?:?]
Caused by: org.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object 'TestDataModel@5b28818c' with class 'TestDataModel' to class 'TestDataModel'
    at org.codehaus.groovy.runtime.typehandling.DefaultTypeTransformation.continueCastOnSAM(DefaultTypeTransformation.java:404) ~[groovy-3.0.20.jar:3.0.20]
    at org.codehaus.groovy.runtime.typehandling.DefaultTypeTransformation.continueCastOnNumber(DefaultTypeTransformation.java:315) ~[groovy-3.0.20.jar:3.0.20]
    at org.codehaus.groovy.runtime.typehandling.DefaultTypeTransformation.castToType(DefaultTypeTransformation.java:243) ~[groovy-3.0.20.jar:3.0.20]
    at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.castToType(ScriptBytecodeAdapter.java:615) ~[groovy-3.0.20.jar:3.0.20]
    at Script16.run(Script16.groovy:9) ~[?:?]
    at org.codehaus.groovy.jsr223.GroovyScriptEngineImpl.eval(GroovyScriptEngineImpl.java:317) ~[groovy-jsr223-3.0.20.jar:3.0.20]

相关代码 #

自定义类TestDataModel #

class TestDataModel {
    private String jmsMessageID;
    private long jmsTimestamp;
    private String targetValue;

    // Constructor
    public TestDataModel(String jmsMessageID, long jmsTimestamp, String targetValue) {
        this.jmsMessageID = jmsMessageID;
        this.jmsTimestamp = jmsTimestamp;
        this.targetValue = targetValue;
    }

    // Getters for accessing private fields
    public String getJmsMessageID() {
        return jmsMessageID;
    }

    public long getJmsTimestamp() {
        return jmsTimestamp;
    }

    public String getTargetValue() {
        return targetValue;
    }
}

该类已通过user.classpath配置项添加到JMeter类路径。

JSR223 Sampler1（存对象） #

import TestDataModel

List<TestDataModel> dataList = new ArrayList<>()

// Example: Adding message data to the list
dataList.add(new TestDataModel("ID1", System.currentTimeMillis(), "Value1"));
dataList.add(new TestDataModel("ID2", System.currentTimeMillis(), "Value2"));
dataList.add(new TestDataModel("ID3", System.currentTimeMillis(), "Value3"));


    // Example: Searching for a specific targetValue
    String targetValue1 = "Value2";
    for (TestDataModel testDataModel : dataList) {
      if (testDataModel.getTargetValue().equals(targetValue1)) {
          log.info("Found message with targetValue: " + targetValue1)
          log.info("JMSMessageID: " + testDataModel.getJmsMessageID())
          log.info("JMSTimestamp: " + testDataModel.getJmsTimestamp())
          break
      } else {
        log.info("Target message with targetValue: " + targetValue1 + " was not found")
        }
    }
    
    vars.putObject("customObject", dataList)
    
    def retrievedCustomObject = vars.getObject("customObject")
    
    
    // Example2: Searching for a specific targetValue
    String targetValue2 = "Value3";
    for (TestDataModel testDataModel : retrievedCustomObject) {
      if (testDataModel.getTargetValue().equals(targetValue2)) {
          log.info("Found message with targetValue: " + targetValue2)
          log.info("JMSMessageID: " + testDataModel.getJmsMessageID())
          log.info("JMSTimestamp: " + testDataModel.getJmsTimestamp())
          break
      } else {
        log.info("Target message with targetValue: " + targetValue2 + " was not found")
        }
    }

JSR223 Sampler2（读对象） #

import TestDataModel

// Retrieve the customObject object from JMeter variables
def customObject = vars.getObject("customObject");

// Check if the object is not null
if (customObject != null) {
    // Iterate over the customObject
    for (TestDataModel data : customObject) {
        // Access data properties and perform actions as needed
        log.info("JMSMessageID: " + data.getJmsMessageID() + ", JMSTimestamp: " + data.getJmsTimestamp() + ", Value: " + data.getTargetValue());
        // Perform further processing here
    }
} else {
    log.info("customObject is null or not found in JMeter variables.");
}

问题原因 #

核心原因是类加载器冲突：

• JMeter的每个JSR223采样器默认使用独立的Groovy脚本引擎类加载器，尽管类名都是TestDataModel，但不同采样器中该类由不同类加载器加载，JVM会判定为两个完全不同的类，因此无法完成类型转换。
• 同一采样器内类加载器一致，所以存取对象操作正常；跨采样器时类加载器不同，触发类型转换异常。

解决方案 #

方案1：统一使用JMeter共享类加载器 #

修改每个JSR223采样器的脚本编译设置：

• 在采样器配置界面，找到Compile script locally选项，取消勾选（默认可能处于勾选状态）。
• 此设置会让所有JSR223采样器使用JMeter主类加载器加载自定义类，确保类实例的类加载器一致。

方案2：利用Groovy动态特性避免强类型转换 #

修改Sampler2的遍历逻辑，不使用强类型循环，改用Groovy动态遍历：

def customObject = vars.getObject("customObject");

if (customObject != null) {
    customObject.each { data ->
        log.info("JMSMessageID: " + data.getJmsMessageID() + ", JMSTimestamp: " + data.getJmsTimestamp() + ", Value: " + data.getTargetValue());
    }
} else {
    log.info("customObject is null or not found in JMeter variables.");
}

Groovy的动态特性会通过反射调用方法，绕过类加载器导致的类型检查问题。

方案3：将自定义类打包为Jar放入JMeter lib目录 #

• 将TestDataModel类编译成Jar文件，放到JMeter安装目录的lib或lib/ext文件夹下。
• 重启JMeter后，该类会由JMeter系统类加载器加载，所有采样器共享同一个类定义，彻底避免类加载器冲突。

内容的提问来源于stack exchange，提问作者JustNatural