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 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 hashMap = JSON.parseObject(byJSONString, HashMap.class);
HashMap 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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