Multiple list for fetching image file from different directory

Have different images in various folder categorized according to the size of the folder. And Each folder have multiple directory like CX and MX OR VX. Each of this CX/MX/VX have SER00001, SER00002, SER00003 And each of this folder have all the images.

Use Case:

1. Select any random directory of any size, like 5MB or 30MB or 1GB
2. Each 5MB/30MB/1Gb folder have folder like CX, MX or VX.
3. Each CX/MX/VX have SER00001/SER00002/SER00003... folders.
4. Each SER00001/SER00002/SER00003... folders contain the images.
5. Based upon the selection like all or single the CX, MX or VX will be selected like for all all the CX,VX & MX will be selected and inside all the folder eventually the images under it. Now for single only one from CX,VX and MX will be selected and and all the SER folder and eventually the images under it

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import groovy.io.FileType;
def dir = new File(vars.get("dirName"));
def selectionPattern = ["All","Single"];
def list = [];
def listNew = [];
def list_series = [];
def list_images = [];
def modalityDir = [];
def modalityFileName = [];
def finalModalityName = [];
def rnd = new Random();
def rndSelect = new Random();
def userSelectionForModalityFolder = selectionPattern[rndSelect.nextInt(selectionPattern.size())];
if (userSelectionForModalityFolder === "All") {
dir.eachDir() {
dirList ->
list << dirList
}
def randomParentDirectorySelected = list[rnd.nextInt(list.size())];
randomParentDirectorySelected.eachDir() {
listDir ->
list_series << listDir
}
for (allSelectionDir in list_series) {
allSelectionDir.eachDir() {
allSelectDirectory ->
list_images << allSelectDirectory
}
}
for (int b = 0; b < list_images.size(); b++) {
File[] modalityFiles = list_images[b].listFiles();
modalityFileName << modalityFiles
}
for (int n = 0; n < modalityFileName.size(); n++) {
for (int p = 0; p < modalityFileName[n].size(); p++) {
finalModalityName << modalityFileName[n]

}
}
vars.putObject("All_Modality",finalModalityName);
} else {
dir.eachDir() {
dirList ->
list << dirList
}
def randomParentDirectorySelected = list[rnd.nextInt(list.size())]
randomParentDirectorySelected.eachDir() {
secDirList ->
listNew << secDirList
}
if (listNew.size() > 2) {
def totalFile = ranSelect.nextInt(listNew.size());
} else {
Random ranSelect = new Random();
def totalFile = ranSelect.nextInt(listNew.size() + 4);
def random_ModalitySelection = listNew[rnd.nextInt(listNew.size())]
random_ModalitySelection.eachDir() {
modalityD ->
modalityDir << modalityD
}
for (int i = 0; i < modalityDir.size(); i++) {
File[] modalityFiles = modalityDir[i].listFiles();
modalityFileName << modalityFiles
}
for (int j = 0; j < modalityFileName.size(); j++) {
for (int k = 0; k < modalityFileName[j].size(); k++) {
finalModalityName << modalityFileName[j][k]
}
}
vars.putObject("All_Modality",finalModalityName);
}
}

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This code work fine but I have declared too many list inside my code, when I am running for large number of image file I am getting longer response in the code

1. I don't think it's a good idea to use random data because I believe tests need to be repeatable and with your approach if you detect a performance issue you will have to take extra steps to replay the test scenario
2. If generating the list is time/resource consuming you could move it to setUp Thread Group to pre-generate the list of files for each virtual user and write it to the CSV file. Then in the main Thread Group you can use CSV Data Set Config, it will be the fastest option and will give you the repeatability mentioned in the point 1.