Passing dynamic method name to another method as parameter in java

Question

I have a calling method as genJsonPayload(). Inside this method I am calling a replace() method to replace some string with randomly generated values. I want to call the replace() by passing another method as parameter. My sample code below.

public static StringBuffer replace(String jsonparam, StringBuffer jsondata, String replacedWith) { 
    int start = 0;
    int last = 0;
    while (jsondata.indexOf(jsonparam)!= jsondata.lastIndexOf(jsonparam)) {
        start = jsondata.indexOf(jsonparam);
        last = start + jsonparam.length();
        jsondata = jsondata.replace(start,last,replacedwith); 
    }
    start = jsondata.indexOf(jsonparam);
    last = start + jsonparam.length();
    jsondata = jsondata.replace(start,last,replacedwith); 
    
    return jsondata;
}
    
public String genJSONPayload(String jsonpayload) {
    StringBuffer sbuffer = new StringBuffer(jsonpayload);
    
    try {
        jsondata = replace("expectedAreaCode",jsondata, CreateRandom.createAreaCDRandom());
    }
    catch (Exception e) {
        ....
    }
    try {
        jsondata = replace("expectedextensionNo",jsondata, CreateRandom.createExtensionNumberRandom());
    }
    catch (Exception e) {
        ....
    }
}

Json payload as below:

{
    ...
    ...
    "phonenumber": [
    {
     "areaCode": "expectedAreaCode",
     "extensionNo": "expectedextensionNo",
      ...
    }
    {
     "areaCode": "expectedAreaCode",
     "extensionNo": "expectedextensionNo",
      ...
    }
    {
     "areaCode": "expectedAreaCode",
     "extensionNo": "expectedextensionNo",
      ...
    }],
    ...
    ...
    
}

Note: CreateRandom.createAreaCDRandom() return a random String.

Problem statement: My requirement is to replace "expectedAreaCode" of json file with randomly generated area code using the replace() method. But as I am executing the CreateRandom.createAreaCDRandom() from genJSONPayload() only once so replacedWith in replace() method is getting store with fixed area code and for all the area code in the json array phonenumber, I am getting the same areacode.

Question:

Instead of passing the replacedWith String to the replace() method, can I pass the createAreaCDRandom() static method as parameter and instead of executing createAreaCDRandom() method from genJSONPayload, then I will execute it inside replace method multiple times inside the while loop. I have more than 5 such random mentods, basically for different json parameters. How can I pass the createAreaCDRandom(), createExtensionNumberRandom(), etc methods as the parameter in the repace() method?

Answer 1

Use Supplier class as a method parameter ( https://docs.oracle.com/javase/8/docs/api/java/util/function/Supplier.html ).

Then You can pass lambda or method reference to provide value generating logic.

public static StringBuffer replace(String jsonparam, StringBuffer jsondata, Supplier<String> supplier) {
    int start = 0;
    int last = 0;
    while (jsondata.indexOf(jsonparam) != jsondata.lastIndexOf(jsonparam)) {
        start = jsondata.indexOf(jsonparam);
        last = start + jsonparam.length();
        jsondata = jsondata.replace(start, last, supplier.get());
    }
    start = jsondata.indexOf(jsonparam);
    last = start + jsonparam.length();
    jsondata = jsondata.replace(start, last, supplier.get());

    return jsondata;
}


public String genJSONPayload(String jsonpayload) {
    StrignBuffer sbuffer = new StrignBuffer(jsonpayload);

    try{
        jsondata = replace("expectedAreaCode",jsondata, CreateRandom::createAreaCDRandom);
    }
    catch(Exception e){
        ....
    }
    try{
        jsondata = replace("expectedextensionNo",jsondata, CreateRandom::createExtensionNumberRandom);
    }
    catch(Exception e){
        ....
    }
}