Fastjson's tojsonstring() source code analysis for special processing of time classes - "deepnova developer community"

author ： Hezijiang

1. Background introduction
   This article is in the process of project iteration , Found an interesting bug Caused by the source code analysis , Here with a little face , Look at the fastjson Source code
2. case analysis
   2.1 The process of finding problems
   In project use , Find out about Timestamp The type of toJSONString() When the method is called , The output structure is not displayed as expected , Later, it will be dismantled separately demo To do research

public static void main(String[] args) {
Timestamp timestamp = new Timestamp(System.currentTimeMillis());
JSONObject jsonObject = new JSONObject();
jsonObject.put(“timestamp”,timestamp);
System.out.println(jsonObject.toJSONString());
}

expect ： Output Timestamp Class tostring Information

actual ： The output is Timestamp The timestamp long value

2.2 debug Process and code analysis
When we meet people who think differently from us , We need to see how the source code is implemented . My first reaction here is fastjson Of bug, Then we need to verify that this is fastjson Of bug Or is it its own strategy
Call stack trace

public String toJSONString() {
SerializeWriter out = new SerializeWriter();

    String var2;
    try {
        (new JSONSerializer(out)).write(this);
        var2 = out.toString();
    } finally {
        out.close();
    }

    return var2;
}

It's direct here new A serialization writer Object to write operation , Click in and continue to see

public final void write(Object object) {
if (object == null) {
this.out.writeNull();
} else {
Class<?> clazz = object.getClass();
ObjectSerializer writer = this.getObjectWriter(clazz);

        try {
            writer.write(this, object, (Object)null, (Type)null, 0);
        } catch (IOException var5) {
            throw new JSONException(var5.getMessage(), var5);
        }
    }
}

Here's one ObjectSerializer Object is more important , Here is also the beginning to enter the core method

You can find it here ObjectSerializer Interfaces have many implementation classes , after debug Find us Timestamp The corresponding serialization class is DateCodec

Click to continue to watch , It is obvious to find some real implementation logic
Here are some if else To realize some inheritance Date The serialization operation of some classes of class , among WriteDateUseDateFormat WriteClassName UseISO8601DateFormat these SerializerFeature Enumeration classes play a very important role , At this time, we finally found that fastjson about date The implementation class of has special serialization operations , Here we need to make some special configurations to complete toJSONString The implementation of the .

2.3 Solution Research
1. encounter date Implementation class of , Own business use related tostring Method , Do not use native types , Use string replace

2. configuration-dependent SerializerFeature Use fastjson Class of

3. The comparison of the two schemes
   3.1 encounter date Implementation class of , Own business use related tostring Method , Do not use native types , Use string replace
   
   Execution results ：
   

The elapsed time ： 98ms

3.2 configuration-dependent SerializerFeature Use fastjson Class of

Execution results ：

The elapsed time ：113ms

4. Conclusion
   fastjson There is no advantage in dealing with time types , We are using fastjson Pay attention to when printing time type , In the course of business , If you have requirements for time type, you'd better convert it yourself , In this way, the output is intuitive and easy to control , Time zone processing is also more flexible , The threshold is still low . Of course, this is only my personal opinion , There are different opinions to exchange .