Fastjson. Methods and source code analysis for the processing of underline and hump problems

I. Preface

In the development process often encountered JSON parsing and generation problems, so you have been using Fastjson to achieve this function.

However, a recent problem has been encountered:

1. Many of the data inside the JSON string are "_" underlined, for example, op_id.

2. And in Java, a lot of the hump is written, such as Opid

Can these two match and then parse?

Two. Workaround for HTTP requests

The HTTP request has a @jsonproperty annotation, but this annotation, Fastjson, is not recognized.

Three. Smart Matching

Fastjson provides smart matching rules, which are automatically mapped

Op_id->opid->ipid

This means that even if the JSON string is ' op_id ', the Java variable can be opid or opid, and then the corresponding data can be obtained.

As follows:

public class Runme {static int one_day_seconds = $ * $ * 1000;public static void Main (string[] args) {String json = "{\" op-id\ ": 1000}"; Mo mo = json.parseobject (JSON, Mo.class); System.out.println (Mo.getopid ());} public static class Mo {private string Opid;public string Getopid () {return opid;} public void Setopid (String opid) {this.opid = Opid;}}}

Four. Principle Analysis

How did the Fastjson do it?

Read the next source code

Https://github.com/alibaba/fastjson

The logic of discovering it is as follows:

Files: Src/main/java/com/alibaba/fastjson/parser/deserializer/javabeandeserializer.java

Method: Smartmatch (String key, int[] setflags)

Public fielddeserializer smartmatch (string key, int[] setflags)  {         if  (key == null)  {             return null;        }                 fielddeserializer  fielddeserializer = getfielddeserializer (key, setflags);         if  (fielddeserializer == null)  {             long smartkeyhash = typeutils.fnv1a_64_lower (Key);             if  (this.smartmatchhasharray ==  null)  {                 long[] hashArray = new long[sortedfielddeserializers.length];                 for  (int i = 0; i <  sortedfielddeserializers.length; i++)  {                     hasharray[i] = typeutils.fnv1a_64_lower ( Sortedfielddeserializers[i].fieldinfo.name);                 }                 arrays.sort (Hasharray);                 this.smartMatchHashArray = hashArray;             }             // smartmatchhasharraymapping            int pos =  Arrays.binarysearch (Smartmatchhasharray, smartkeyhash);             boolean is = false;             if  (pos < 0 &&  (Is = key.startswith ("is" )))  {                 Smartkeyhash = typeutils.fnv1a_64_lower (key.substring (2));                 pos = arrays.binarysearch (SmartMatchHashArray,  smartkeyhash);            }             if  (pos >= 0)  {                 if  (Smartmatchhasharraymapping == null)  {                     short[] mapping = new short[smartMatchHashArray.length];                      Arrays.fill (mapping,  (short)  -1);                     for  (int i = 0; i <  sortedfielddeserializers.length; i++)  {                         int p =  arrays.binarysearch (smartmatchhasharray                                 ,  Typeutils.fnv1a_64_lower (sortedfielddeserializers[i].fieldinfo.name));                         if   (p >= 0)  {             &NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;MAPPING[P]  =  (short)  i;                         }                     }                      Smartmatchhasharraymapping = mapping;                }                 int deserindex =  smartMatchHashArrayMapping[pos];                 if  (deserindex != -1)  {                     if  (!issetflag (Deserindex,  setflags))  {                         fieldDeserializer =  sortedfielddeserializers[deserindex];                     }                 }            }             if  (fielddeserializer != null)  {                 FieldInfo fieldInfo =  fielddeserializer.fieldinfo;                 if  ((Fieldinfo.parserfeatures & feature.disablefieldsmartmatch.mask)  != 0)  {                     return null;                 }                 Class fieldClass = fieldInfo.fieldClass;                 if  (is &&  (fieldclass !=  Boolean.class && fieldclass != boolean.class))  {                      fielddeserializer = null;                 }            }         }        return  fielddeserializer;    }

An important part of this is calling the Typeutils.fnv1a_64_lower (String) method, calculating the incoming key (op_id) and the defined Java member variable opid, and then calculating whether they match.

If it matches, it will be overwritten.

So the key is to implement the Typeutils.fnv1a_64_lower (String) method, as follows:

This method is if it is ' _ ' or '-', then ignore, that is, if it is op_id, then it will become opid.

If it is uppercase, then it is converted to lowercase, that is, opid, it becomes opid.

So Op-id or op_id can match opid or opid.

Public static long fnv1a_64_lower (String key) {         long hashcode = 0xcbf29ce484222325l;        for ( Int i = 0; i < key.length ();  ++i) {             char ch = key.charat (i);             if (ch ==  ' _ '  | |  ch ==  '-') {                 continue;            }             if (ch >=  ' A '  &&  ch <=  ' Z ') {                 ch =  (char)   (CH&NBSP;+&NBSP;32);             }             hashCode ^= ch;             hashCode *= 0x100000001b3L;        }         return hashcode;    }

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Fastjson. Methods and source code analysis for the processing of underline and hump problems