Tutorial on using Jackson to convert Java objects to JSON _java

One, Getting Started
Jackson has a objectmapper class that is useful for the interchange of Java objects with JSON.
1.JAVA Object Json[json serialization]

Import java.io.IOException; 
Import java.text.ParseException; 
 
Import Java.text.SimpleDateFormat; 
 
Import Com.fasterxml.jackson.databind.ObjectMapper;  public class Jacksondemo {public static void main (string[] args) throws ParseException, IOException {User user = 
    New User ();  
    User.setname ("Wang"); 
    User.setemail ("xiaomin@sina.com"); 
     
    User.setage (20); 
    SimpleDateFormat DateFormat = new SimpleDateFormat ("Yyyy-mm-dd");     
     
    User.setbirthday (Dateformat.parse ("1996-10-01")); 
     /** * Objectmapper is the core of the JSON operation, and all of Jackson's JSON operations are implemented in Objectmapper. 
     * Objectmapper has multiple JSON serialization methods that can save JSON strings in different media, such as file, OutputStream, and so on. 
     * WriteValue (file arg0, Object arg1) turns arg1 into a JSON sequence and saves it to the arg0 file. 
     * WriteValue (OutputStream arg0, Object arg1) turns arg1 into a JSON sequence and saves it to the arg0 output stream. 
     * Writevalueasbytes (Object arg0) turns arg0 into a JSON sequence and outputs the result as a byte array. 
     * Writevalueasstring (Object arg0) turns arg0 into a JSON sequence and outputs the result as a string. * * Objectmapper mapper = new Objectmapper (); User class to JSON//output result: {"name": "Min", "Age": "Birthday": 844099200000, "email": "xiaomin@sina.com"} String JSON = Mapp 
    er.writevalueasstring (user); 
     
    SYSTEM.OUT.PRINTLN (JSON); Java set goto JSON//output result: [{"Name": "Min", "Age": "Birthday": 844099200000, "email": "xiaomin@sina.com"}] List<user&gt ; 
    Users = new arraylist<user> (); 
    Users.add (user); 
    String jsonlist = mapper.writevalueasstring (users); 
  System.out.println (jsonlist); 

 } 
}

2.JSON turn Java class [JSON deserialization]

Import java.io.IOException; 
Import java.text.ParseException; 
Import Com.fasterxml.jackson.databind.ObjectMapper; 
 
public class Jacksondemo {public 
  static void Main (string[] args) throws ParseException, IOException { 
    String JSON = "{\" name\ ": \" Wang ", \" age\ ": 20,\" birthday\ ": 844099200000,\" email\ ": \" Xiaomin@sina.com\ "}"; 
     
    /** 
     * Objectmapper supports JSON deserialization of data from byte[], File, InputStream, strings, and so on. 
     */ 
    Objectmapper mapper = new Objectmapper (); 
    User user = Mapper.readvalue (JSON, user.class); 
    SYSTEM.OUT.PRINTLN (user); 
  } 
 

Second, Jackson support 3 ways to use:
1, Data Binding: The most convenient to use.
(1) Full Data Binding:

private static final String model_binding = "{\ name\": \ "name1\", \ "type\": 1} "; 
  public void Fulldatabinding () throws exception{ 
    objectmapper mapper = new Objectmapper (); 
    Model user = Mapper.readvalue (model_binding, Model.class);//readvalue to an entity class. 
    System.out.println (User.getname ()); 
    System.out.println (User.gettype ()); 
  } 

Model class:

private static class model{ 
    private String name; 
    private int type; 
     
    Public String GetName () {return 
      name; 
    } 
    public void SetName (String name) { 
      this.name = name; 
    } 
    public int GetType () {return 
      type; 
    } 
    public void SetType (int type) { 
      this.type = type; 
    } 
  } 

(2) Raw Data Binding:

/** 
  Concrete Java types that Jackson would use for simple data binding are: 
  JSON type    java type 
  object     linkedhashmap<string,object> 
  Array      arraylist<object> 
  string     string number 
  (no Fraction) Integer, Long or BigInteger (smallest applicable) number 
  (fraction)  Double (configurable to use BigDecimal) 
  true|false   Boolean 
  null      null 
  * 
  /public void rawdatabinding () throws exception{ 
    Objectmapper mapper = new Objectmapper (); 
    HashMap map = Mapper.readvalue (model_binding,hashmap.class);//readvalue to an original data type. 
    System.out.println (Map.get ("name")); 
    System.out.println (Map.get ("type")); 
  } 

(3) Generic Data Binding:

private static final String generic_binding = "{\ key1\": {\ "name\": \ "name2\", \ "type\": 2},\ "key2\": {\ "name\": \ "name3\ ", \" Type\ ": 3}}"; 
  public void Genericdatabinding () throws exception{ 
    objectmapper mapper = new Objectmapper (); 
    hashmap<string,model> Modelmap = Mapper.readvalue (Generic_binding,new typereference 
 

2, Tree Model: the most flexible.

private static final String tree_model_binding = "{\ treekey1\": \ "treevalue1\", \ "treekey2\": \ "treevalue2\", \ " 
  Children\ ": [{\" childkey1\ ": \" Childkey1\ "}]}"; 
    public void Treemodelbinding () throws exception{objectmapper mapper = new Objectmapper (); 
    Jsonnode RootNode = Mapper.readtree (tree_model_binding); 
    Path is the same as get, but returns missing node instead of NULL when the node is not found. String Treekey2value = Rootnode.path ("Treekey2"). Gettextvalue ()//System.out.println ("Treekey2value:" + treekey2val 
    UE); 
    Jsonnode Childrennode = Rootnode.path ("Children"); 
    String childkey1value = childrennode.get (0). Path ("Childkey1"). Gettextvalue (); 
     
    System.out.println ("Childkey1value:" +childkey1value); 
    Create root node Objectnode root = Mapper.createobjectnode (); 
    Create child nodes 1 Objectnode node1 = Mapper.createobjectnode (); 
    Node1.put ("Nodekey1", 1); 
    Node1.put ("Nodekey2", 2); 
    Binding child nodes 1 root.put ("Children", node1); Array node Arraynode Arraynode = Mapper.createarraynodE (); 
    Arraynode.add (Node1); 
    Arraynode.add (1); 
    Binding array Node Root.put ("Arraynode", Arraynode); 
    JSON reads to the tree node Jsonnode valuetotreenode = Mapper.valuetotree (tree_model_binding); 
    Bind JSON node Root.put ("Valuetotreenode", Valuetotreenode); 
    JSON binds to the JSON node object Jsonnode bindjsonnode = Mapper.readvalue (generic_binding, jsonnode.class);//bind JSON to the JSON node object. 
    Bind JSON node Root.put ("Bindjsonnode", Bindjsonnode); 
  System.out.println (mapper.writevalueasstring (root)); 
 }

3, streaming API: Best performance.
 
for performance-demanding programs, it is recommended that you use a streaming API, otherwise use jsonfactory, either for creating Jsongenerator or Jsonparser.

Package Com.jingshou.jackson; 
Import Java.io.File; 
 
Import java.io.IOException; 
Import com.fasterxml.jackson.core.JsonEncoding; 
Import Com.fasterxml.jackson.core.JsonFactory; 
Import Com.fasterxml.jackson.core.JsonGenerator; 
Import Com.fasterxml.jackson.core.JsonParser; 
 
Import Com.fasterxml.jackson.core.JsonToken; public class JacksonTest6 {public static void main (string[] args) throws IOException {Jsonfactory jfactory = n 
      
    EW jsonfactory (); /*** write to file ***/jsongenerator jgenerator = jfactory.creategenerator (new file ("C:\\user.json"), JSON 
    ENCODING.UTF8); Jgenerator.writestartobject ();  {Jgenerator.writestringfield ("name", "Mkyong");//"name": "Mkyong" Jgenerator.writenumberfield ("Age", 29); "Age": Jgenerator.writefieldname ("messages"); "Messages": Jgenerator.writestartarray (); [Jgenerator.writestring ("MSG 1");//"MSG 1" jgenerator.writestring ("MSG 2");//"MsG 2 "Jgenerator.writestring (" MSG 3 "); "MSG 3" Jgenerator.writeendarray (); ] Jgenerator.writeendobject (); 
     
    } jgenerator.close (); 
    /*** read from file ***/jsonparser jparser = jfactory.createparser (new file ("C:\\user.json"));  Loop until token equal to '} ' while (Jparser.nexttoken ()!= jsontoken.end_object) {String fieldname = 
      Jparser.getcurrentname (); 
       if ("Name". Equals (fieldname)) {//Current token are ' name ',//move to Next, which is ' name ' ' s value 
       Jparser.nexttoken (); System.out.println (Jparser.gettext ());  
       Display Mkyong} if (' Age '. Equals (fieldname)) {//Current token is ' age ', 
       Move to Next, the which is "name" ' s value jparser.nexttoken (); System.out.println (Jparser.getintvalue ()); Display ' if (' Messages '. Equals (fieldname)) {Jparser.nexttoken ();//CurreNT token is ' [', move next//messages are array, loop until token equal to '] ' while (jparser.nexttok En ()!= Jsontoken.end_array) {//Display MSG1, MSG2, MSG3 System.out.println (jparser.gettext  
    
       ()); 
 
  }} jparser.close (); 
 } 
 
}