Shulou(Shulou.com)06/02 Report--

This article mainly introduces "the detailed introduction of Json and the tutorial of using fastjson". In the daily operation, I believe that many people have doubts about the detailed introduction of Json and the tutorial of using fastjson. The editor has consulted all kinds of materials and sorted out simple and easy-to-use methods of operation. I hope it will be helpful to answer the doubts of "detailed introduction of Json and tutorial of fastjson". Next, please follow the editor to study!

Json is a lightweight data exchange format, which uses a text format of "key: value" pairs to store and represent data. It is often used in the process of system data exchange, and is an ideal data exchange language. When using Java for Web development, it is inevitable to encounter the use of Json. Let's briefly talk about the use of Json and the use of fastjson.jar packages.

One: JSON form and grammar 1.1:JSON object

Let's first look at the following data:

{"ID": 1001, "name": "Zhang San", "age": 24}

The first data is a Json object. If you look at its data form, you can get the following syntax:

1: the data is in curly braces

2: data appears in the form of "key: value" pairs (where keys are mostly in the form of strings, values can be strings, numeric values, or even other json objects)

3: every two key: value pairs are separated by commas (the last key: value pair omits commas)

Follow the above three points and you can form a json object.

1.2:JSON object array

Next, let's look at the second data and look at its data form, and we can get the following syntax:

[{"ID": 1001, "name": "Zhang San", "age": 24}, {"ID": 1002, "name": "Li Si", "age": 25}, {"ID": 1003, "name": "Wang Wu", "age": 22}]

1: the data is in square brackets (can be understood as an array)

2: each data in square brackets appears as a json object

3: every two pieces of data are separated by commas (the last one does not need a comma)

Observe the above three points to form an array of json objects (and an array in which multiple json objects are stored)

By understanding the above two basic forms, we can arrive at other forms of data, such as the following:

{"Department name": "R & D Department", "Department member": [{"ID": 1001, "name": "Zhang San", "age": 24}, {"ID": 1002, "name": "Li Si", "age": 25}, {"ID": 1003, "name": "Wang Wu", "age": 22}] "Department location": "21 xx Building"}

This is a combination of the above two basic forms of deformation, through this transformation, so that the data encapsulation has great flexibility, allowing developers to freely use their imagination.

1.3:JSON string

JSON strings are also frequently used in normal development. Json strings should meet the following conditions:

1: it must be a string, which is wrapped by "" or "'" to support various operations of the string.

2: the data format should satisfy one of these formats. It can be a json object, an array of json objects, or a combination of two basic forms of deformation.

Summary: json can be simply divided into basic forms: json objects, json object arrays. The combination of the two basic formats transforms into other forms, but it is essentially one of the json objects or an array of json objects. Json objects or object arrays can be converted into json strings, which can be used in different situations.

Note: it is easy to make errors when encapsulating json data, such as carelessly adding a comma at the end of the last piece of data, etc. Here I provide an online verification tool to facilitate you to verify the correctness of the json data format.

Http://www.bejson.com/

Introduction and use of fastjson introduction to 2.1:fastjson and jar download

Fastjson.jar is a package specially developed by Ali's father for Java development, which can easily realize the conversion between json object and JavaBean object, the conversion between JavaBean object and json string, and the conversion between json object and json string. In addition to this fastjson, there are Gson packages developed by Google, and other forms, such as net.sf.json packages, can be transformed into json. The name of the method is different, and the final implementation result is the same.

Convert json strings to json objects JSONObject obj= new JSONObject () .fromObject (jsonStr) that does this in net.sf.json; / / convert json strings to JSONObject obj=JSON.parseObject (jsonStr) that json objects do in fastjson; / / convert json strings to json objects

Today we are mainly about the use of fastjson. First of all, we should import the corresponding fastjson.jar package into the Java project.

Original download address of fastjson.jar package: https://github.com/alibaba/fastjson

Click download on the page to download the latest package

Download address of fastjson.jar package Baidu cloud disk: https://pan.baidu.com/s/1CCGoRCdSjNUDB736cRCDBw

Analysis and use of 2.2:fastjson Source Code

In the package, you can find three main classes, JSON,JSONArray,JSONObject

The relationship between the three is as follows: JSONObject and JSONArray inherit JSON

Observing the inheritance and implementation relationship of this class, it is not difficult to find that JSONObject implements the Map interface, while the data in the json object appears in the form of "key: value" pairs. It can be guessed that the underlying operation of JSONObject is implemented by Map.

Let's look at the main methods in the class:

Looking at the source code, we can see that the internal implementation is mainly implemented by the get (key) method, which is found as follows:

The discovery interior is mainly implemented by the get () method in the Map interface.

Let's take a look at another commonly used method in JSONObject, getInteger (String key), which gets the integer data in the json object, such as the integer value 20. 0 corresponding to age in the "age:20" key-value pair.

Summary: JSONObject corresponds to the json object, through various forms of get () method can get the data in the json object, you can also use methods such as size (), isEmpty () and other methods to obtain the number of "key: value" pairs and determine whether it is empty. Its essence is accomplished by implementing the Map interface and calling the methods in the interface.

Analysis and use of JSONArray Class Source Code

It is mainly realized by the corresponding methods in the List interface.

Like JSONObject, there are some get () methods in JSONArray, but they are not commonly used. The most useful method should be the getJSONObject (int index) method, which is used to get JSONObject objects at a specified location in an array of json objects. Together with the size () method, it can be used to traverse each object in an array of json objects.

Through the above two methods, in conjunction with the for loop, we can achieve the traversal of the array of json objects, of course, JSONArray also implements the iterator method to traverse, which is very similar to the traversal of List.

This method is overloaded many times, but the final goal is to convert json objects to json strings and javabean objects to json strings. Among them, the toJSONString () about the key transient modification is used in the json object serialization process, hoping that some "key: value" is used in the application of the data unchanged.

The parseObject () method of the JSON class, which converts json strings into json objects or javabean objects

This method returns the JSONObject object, which is used to realize the conversion from json string to json object. The parse () method is called internally, and the underlying DefaultJSONParser parsing class is called for conversion. When the conversion fails, a can not cast to JSONObject exception is thrown.

This method can not only realize the transformation from json string to json object, but also realize the transformation from json string to javabean object after overloading.

The conversion between json strings and javaBean can use either the TypeReference class or the Class class.

Student stu1=JSON.parseObject (jsonstr,new TypeReference () {}); Student stu1=JSON.parseObject (jsonstr,Student.class)

I recommend using the second Class class reflection, which is relatively simple.

The JSONArray () method of the JSON class, which converts json strings into an array of json objects or List

Similar to the parseObject () method, parseArray () converts a json string to an array of json objects or to a List containing generics

The toJSON () method of the JSON class to convert a javabean object into a json object

This method is rarely used, and is mainly used to transform javabean objects into json objects, which is internally implemented through collection interfaces such as Map,LinkedHashMap,HashMap.

At this point, the methods in the JSON class are almost explained, and the following Java examples are given to implement the above transformations.

Test class:

Package jsonTest;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import com.alibaba.fastjson.JSON;import com.alibaba.fastjson.JSONArray;import com.alibaba.fastjson.JSONObject;import com.alibaba.fastjson.TypeReference;public class MyJson {public static void main (String [] args) {List list=new ArrayList (); Student student=new Student ("bob", 24) Student student12=new Student ("lily", 23); list.add (student); list.add (student12); System.out.println ("* javaBean to jsonString*"); String str1=JSON.toJSONString (student); System.out.println (str1) System.out.println (JSON.toJSONString (list)); System.out.println (); System.out.println ("* jsonString to javaBean*"); / / Student stu1=JSON.parseObject (str1,new TypeReference () {}); Student stu1=JSON.parseObject (str1,Student.class) System.out.println (stu1); System.out.println (); System.out.println ("* javaBean to jsonObject*"); JSONObject jsonObject1= (JSONObject) JSON.toJSON (student); System.out.println (jsonObject1.getString ("name")) System.out.println (); System.out.println ("* jsonObject to javaBean*"); Student student2=JSON.toJavaObject (jsonObject1, Student.class); System.out.println (student2); System.out.println () System.out.println ("* javaBean to jsonArray*"); List stulist=new ArrayList (); for (int item0)

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.