Gson also support the old java classes which had not support of generics in them for type information. It just work with these legacy classes smoothly.
In this tutorial, I am giving few examples of very common tasks you can perform with Google Gson.
Examples Listing 1) Two ways to create Gson objects 2) Convert Java objects to JSON format 3) Convert JSON to Java Objects 4) Writing an Instance Creator 5) Custom Serialization and De-serialization 6) Pretty Printing for JSON Output Format 7) Versioning Support
Before coming to examples, let’s have a POJO class which we will use in given examples.
public class Employee { private Integer id; private String firstName; private String lastName; private List<String> roles; public Employee(){ } public Employee(Integer id, String firstName, String lastName, Date birthDate){ this .id = id; this .firstName = firstName; this .lastName = lastName; } public Integer getId() { return id; } public void setId(Integer id) { this .id = id; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this .firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this .lastName = lastName; } public List<String> getRoles() { return roles; } public void setRoles(List<String> roles) { this .roles = roles; } @Override public String toString() { return "Employee [id=" + id + ", firstName=" + firstName + ", " + "lastName=" + lastName + ", roles=" + roles + "]" ; } } |
Let’s jump into examples without putting more un-necessary text in between.
1) Two ways to create Gson objects
Gson object can be created in two ways. First way gives you a quick Gson object ready for faster coding, while second way uses
GsonBuilder
to build a more sophisticated Gson object.//First way to create a Gson object for faster coding Gson gson = new Gson(); //Second way to create a Gson object using GsonBuilder Gson gson = new GsonBuilder() .disableHtmlEscaping() .setFieldNamingPolicy(FieldNamingPolicy.UPPER_CAMEL_CASE) .setPrettyPrinting() .serializeNulls() .create(); |
When using
GsonBuilder
, there are plenty of other useful options you can provide to Gson
object. Go ahead and check them out.
2) Convert Java objects to JSON format
To convert the java objects to JSON format, use
toJson()
method.Employee employee = new Employee(); employee.setId( 1 ); employee.setFirstName( "Lokesh" ); employee.setLastName( "Gupta" ); employee.setRoles(Arrays.asList( "ADMIN" , "MANAGER" )); Gson gson = new Gson(); System.out.println(gson.toJson(employee)); Output: { "id" : 1 , "firstName" : "Lokesh" , "lastName" : "Gupta" , "roles" :[ "ADMIN" , "MANAGER" ]} |
3) Convert JSON to Java Objects
To convert the JSON to java object, use
fromJson()
method.Gson gson = new Gson(); System.out.println( gson.fromJson( "{'id':1,'firstName':'Lokesh','lastName':'Gupta','roles':['ADMIN','MANAGER']}" , Employee. class )); Output: Employee [id= 1 , firstName=Lokesh, lastName=Gupta, roles=[ADMIN, MANAGER]] |
4) Writing an Instance Creator
In most of the cases, Gson library is smart enough to create instances even if any class does not provide default no-args constructor. But, if you found any problem using a class having no no-args constructor, you can use
InstanceCreator
support. You need to register the InstanceCreator
of a java class type with Gson first before using it.
For example, Department.java does not have any default constructor.
public class Department { public Department(String deptName) { this .deptName = deptName; } private String deptName; public String getDeptName() { return deptName; } public void setDeptName(String deptName) { this .deptName = deptName; } @Override public String toString() { return "Department [deptName=" +deptName+ "]" ; } } |
And our
Employee
class has reference of Department
as:public class Employee { private Integer id; private String firstName; private String lastName; private List<String> roles; private Department department; //Department reference //Other setters and getters } |
To use
Department
class correctly, you need to register an InstanceCreator
for Department.java as below:class DepartmentInstanceCreator implements InstanceCreator<Department> { public Department createInstance(Type type) { return new Department( "None" ); } } //Now <strong>use the above InstanceCreator</strong> as below GsonBuilder gsonBuilder = new GsonBuilder(); gsonBuilder.registerTypeAdapter(Department. class , new DepartmentInstanceCreator()); Gson gson = gsonBuilder.create(); System.out.println( gson.fromJson( "{'id':1,'firstName':'Lokesh','lastName':'Gupta','roles':['ADMIN','MANAGER'],'department':{'deptName':'Finance'}}" , Employee. class )); Output: Employee [id= 1 , firstName=Lokesh, lastName=Gupta, roles=[ADMIN, MANAGER], department=Department [deptName=Finance]] |
5) Custom Serialization and De-serialization
Many times, we need to write/read the JSON values which are not default representation of java object. In that case, we need to write custom serializer and deserializer of that java type.
In our example, I am writing serializer and deserializer for
java.util.Date
class, which will help writing the Date format in “dd/MM/yyyy” format.
DateSerializer.java
import java.lang.reflect.Type; import java.text.SimpleDateFormat; import java.util.Date; import com.google.gson.JsonElement; import com.google.gson.JsonPrimitive; import com.google.gson.JsonSerializationContext; import com.google.gson.JsonSerializer; public class DateSerializer implements JsonSerializer<Date> { private static final SimpleDateFormat dateFormat = new SimpleDateFormat( "dd/MM/yyyy" ); public JsonElement serialize(Date date, Type typeOfSrc, JsonSerializationContext context) { return new JsonPrimitive(dateFormat.format(date)); } } |
DateDeserializer.java
import java.lang.reflect.Type; import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Date; import com.google.gson.JsonDeserializationContext; import com.google.gson.JsonDeserializer; import com.google.gson.JsonElement; public class DateDeserializer implements JsonDeserializer<Date> { private static final SimpleDateFormat dateFormat = new SimpleDateFormat( "dd/MM/yyyy" ); public Date deserialize(JsonElement dateStr, Type typeOfSrc, JsonDeserializationContext context) { try { return dateFormat.parse(dateStr.getAsString()); } catch (ParseException e) { e.printStackTrace(); } return null ; } } |
Now you can register these serializer and deserializer with
GsonBuilder
as below:GsonBuilder gsonBuilder = new GsonBuilder(); gsonBuilder.registerTypeAdapter(Date. class , new DateSerializer()); gsonBuilder.registerTypeAdapter(Date. class , new DateDeserializer()); |
Complete example of serializer and deserializer is as below:
Employee employee = new Employee(); employee.setId( 1 ); employee.setFirstName( "Lokesh" ); employee.setLastName( "Gupta" ); employee.setRoles(Arrays.asList( "ADMIN" , "MANAGER" )); employee.setBirthDate( new Date()); GsonBuilder gsonBuilder = new GsonBuilder(); gsonBuilder.registerTypeAdapter(Date. class , new DateSerializer()); gsonBuilder.registerTypeAdapter(Date. class , new DateDeserializer()); Gson gson = gsonBuilder.create(); //Convert to JSON System.out.println(gson.toJson(employee)); //Convert to java objects System.out.println(gson.fromJson( "{'id':1,'firstName':'Lokesh','lastName':'Gupta','roles':['ADMIN','MANAGER'],'birthDate':'17/06/2014'}" , Employee. class )); Output: { "id" : 1 , "firstName" : "Lokesh" , "lastName" : "Gupta" , "roles" :[ "ADMIN" , "MANAGER" ], "birthDate" : "17/06/2014" } Employee [id= 1 , firstName=Lokesh, lastName=Gupta, roles=[ADMIN, MANAGER], birthDate=Tue Jun 17 00 : 00 : 00 IST 2014 ] |
6) Pretty Printing for JSON Output Format
The default JSON output that is provide by Gson is a compact JSON format. This means that there will not be any white-space in the output JSON structure. To generate a more readable and pretty looking JSON use
setPrettyPrinting()
in GsonBuilder
.Gson gson = new GsonBuilder().setPrettyPrinting().create(); String jsonOutput = gson.toJson(employee); Output: { "id" : 1 , "firstName" : "Lokesh" , "lastName" : "Gupta" , "roles" : [ "ADMIN" , "MANAGER" ], "birthDate" : "17/06/2014" } |
7) Versioning Support
This is excellent feature you can use, if the class file you are working has been modified in different versions and fields has been annotated with
@Since
. All you need to do is to use setVersion()
method of GsonBuilder
.GsonBuilder gsonBuilder = new GsonBuilder(); gsonBuilder.registerTypeAdapter(Date. class , new DateSerializer()); gsonBuilder.registerTypeAdapter(Date. class , new DateDeserializer()); //Specify the version like this gsonBuilder.setVersion( 1.0 ); Gson gson = gsonBuilder.create(); |
Fields added in various versions in Employee.java
public class Employee { @Since ( 1.0 ) private Integer id; private String firstName; private String lastName; @Since ( 1.1 ) private List<String> roles; @Since ( 1.2 ) private Date birthDate; //Setters and Getters } |
Now test the version feature:
//Using version 1.0 fields gsonBuilder.setVersion( 1.0 ); Output: { "id" : 1 , "firstName" : "Lokesh" , "lastName" : "Gupta" } ///////////////////////////////////////////////////////////// //Using version 1.1 fields gsonBuilder.setVersion( 1.1 ); Output: { "id" : 1 , "firstName" : "Lokesh" , "lastName" : "Gupta" , "roles" :[ "ADMIN" , "MANAGER" ]} ///////////////////////////////////////////////////////////// //Using version 1.2 fields gsonBuilder.setVersion( 1.2 ); Output: { "id" : 1 , "firstName" : "Lokesh" , "lastName" : "Gupta" , "roles" :[ "ADMIN" , "MANAGER" ], "birthDate" : "17/06/2014" } |
That’s all for this very useful java library to convert java objects from /to JSON structure. Drop a comment is you have any query or feedback.
Source: programming-free.com/2013/03/ajax-fetch-data-from-database-in-jsp.html
Source: programming-free.com/2013/03/ajax-fetch-data-from-database-in-jsp.html
2 nhận xét
Write nhận xétSlot Machines - Jeopardy Casino
ReplyYou'll never be able to play slot 수원 출장안마 machines in this state, but you'll find 보령 출장샵 plenty 광양 출장안마 of fun to play. It's an ideal option 안동 출장샵 for anyone 세종특별자치 출장샵 with a gaming passion for
Cơ Bản Về Gson Json - Mobi Wed >>>>> Download Now
Reply>>>>> Download Full
Cơ Bản Về Gson Json - Mobi Wed >>>>> Download LINK
>>>>> Download Now
Cơ Bản Về Gson Json - Mobi Wed >>>>> Download Full
>>>>> Download LINK 4w
ConversionConversion EmoticonEmoticon