How to retieve specify data from String Entity-CodePudding

I have some value for parsing, for example :

Student{id=19, groupId=1, firstName='Alex', lastName='Sparrow'}

I want to parse this String and get new Arraylist, that will have 1,Alex,Sparrow.

Only this data.

I want to make general parser even if comes some other object f.e. Group{id=22, groupName="BKS",groupCity="Moscow"};

I also will be able to parse it and get List BKS,groupCity,Moscow.

Maybe I can use StringBuilder for it but I am not sure.

CodePudding user response：

In case you only want to get only attribute values. You can consider parse by key-value.

Student{id=19, groupId=1, firstName='Alex', lastName='Sparrow'}

Get the string in {}

id=19, groupId=1, firstName='Alex', lastName='Sparrow'

Then split by ",", you will get array of key=value.

Use loop to continue to split key and value by =

for(string item: data.split(",")){
    String[] keyValues = item.split("=")
    String key = keyValues[0];
    String value = keyValues[1];
}

In case you want to convert to DTO or Pojo, You will have more step to convert key-value to object field.

you can use java reflection to set value for field by name.

https://www.oracle.com/technical-resources/articles/java/javareflection.html

CodePudding user response：

If you have string:

String string = "Student{id=19, groupId=1, firstName='Alex', lastName='Sparrow'}";

Use regular expression to clear string from whitespaces, text before {, and { and } characters itself (it may need adjustments if value or key can contain whitespaces) with:

string = string.replaceAll("\\s|.*\\{|\\}","");

Create a map, which is perfect for key-value pairs, makes it easy and fast to get value based on key. Additionaly HashMap will also ensure that keys are unique:

Map<String,String> map = new HashMap<>();

Populate map with splitted string data:

for (String item : string.split(",")){
        map.put(item.split("=")[0],item.split("=")[1]);
}

Now you can get your data with map.get(String key). For example:

map.get("groupId");

And use all map methods as described in: https://docs.oracle.com/javase/8/docs/api/java/util/Map.html