How to convert between HashMap and String in Java?

Background:

When we need to convert HashMap to String in Json format, remember not to use the toString() method of HashMap. You need to use FastJson/Gson to convert HashMap to String. If you use the toString() method for conversion, you cannot convert the string into a HashMap. It will only cause a serialization error:

demo code:

        HashMap<String, String> dataMap = new HashMap<>(4);
        dataMap.put("key1", "value1");
        dataMap.put("key2", "value2");
        dataMap.put("key3", "value3");
        dataMap.put("key4", "value4");

        String byToString = dataMap.toString();
        String byJSONString = JSON.toJSONString(dataMap);
        System.out.println(byToString);
        System.out.println(byJSONString);

        HashMap<String ,String> hashMap = JSON.parseObject(byJSONString, HashMap.class);
        HashMap<String ,String> hashMap2 = JSON.parseObject(byToString, HashMap.class);

log:

{key1=value1, key2=value2, key3=value3, key4=value4}
{"key1":"value1","key2":"value2","key3":"value3","key4":"value4"}

Further execution, visible through Debug:

Convert String to HashMap by converting FastJson to String, but converting toString will report serialization errors.

Reason:

HashMap toString source code:

HashMap overrides the toString method of the base class. The principle is through a for loop. Connect key and value with = and output. Obviously this is not a Json string format.

JSON.toJSONString(Object object) source code:

FastJson can convert the Object object into a string in Json format through the toJSONString method, and vice versa, you can use Serialization/deserialization method converts Json string into original object.

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