Gson序列化範例

在本章中，我們將討論和學習如何使用陣列，集合和泛型的序列化/反序列化。

1. 陣列

int[] marks = {100,90,85}; 

//Serialization 
System.out.println("marks:" + gson.toJson(marks));        

//De-serialization 
marks = gson.fromJson("[100,90,85]", int[].class); 
System.out.println("marks:" + Arrays.toString(marks));

範例

我們來看看陣列的序列化/反序列化。 建立一個名為GsonTester的Java類檔案:GsonTester.java -

import java.util.Arrays; 
import com.google.gson.Gson;  

public class GsonTester { 
   public static void main(String args[]) { 
      Gson gson = new Gson(); 
      int[] marks = {100,90,85}; 
      String[] names = {"Maxsu","Yiibai","Mohan"}; 

      //Serialization 
      System.out.print("{"); 
      System.out.print("marks:" + gson.toJson(marks) + ",");       
      System.out.print("names:" + gson.toJson(names));       
      System.out.println("}");  

      //De-serialization 
      marks = gson.fromJson("[100,90,85]", int[].class); 
      names = gson.fromJson("[\"Maxsu\",\"Yiibai\",\"Mohan\"]", String[].class);
      System.out.println("marks:" + Arrays.toString(marks)); 
      System.out.println("names:" + Arrays.toString(names));     
   }      
}

執行上面範例程式碼，得到以下結果 -

{marks:[100,90,85],names:["Maxsu","Yiibai","Mohan"]} 
marks:[100, 90, 85] 
names:[Maxsu, Yiibai, Mohan]

2. 集合

List marks = new ArrayList(); 

//Serialization 
System.out.println("marks:" + gson.toJson(marks));        

//De-serialization 
//get the type of the collection. 
Type listType = new TypeToken<list>(){}.getType(); 

//pass the type of collection 
marks = gson.fromJson("[100,90,85]", listType); 
System.out.println("marks:" +marks);</list>

讓我們看看集合(Collection)序列化/反序列化的實際操作。 建立一個名為GsonTester的Java類檔案: GsonTester.java -

import java.lang.reflect.Type; 
import java.util.ArrayList; 
import java.util.Collection;  

import com.google.gson.Gson; 
import com.google.gson.reflect.TypeToken;  

public class GsonTester { 
   public static void main(String args[]) { 
      Gson gson = new Gson(); 
      Collection<Integer> marks = new ArrayList<Integer>();  
      marks.add(100); 
      marks.add(90); 
      marks.add(85);  

      //Serialization 
      System.out.print("{"); 
      System.out.print("marks:" + gson.toJson(marks));             
      System.out.println("}");  

      //De-serialization 
      Type listType = new TypeToken<Collection<Integer>>(){}.getType(); 
      marks = gson.fromJson("[100,90,85]", listType); 
      System.out.println("marks:" +marks);     
   }      
}

執行上面範例程式碼，得到以下結果 -

{marks:[100,90,85]} 
marks:[100, 90, 85]

3. 泛型

Gson使用Java反射API來獲取要將Json文字對映到的物件的型別。 但是在泛型中，這些資訊在序列化過程中丟失了。 為了解決這個問題，Gson提供了一個com.google.gson.reflect.TypeToken類來儲存通用物件的型別。

範例

讓我們來看看泛型序列化/反序列化。 建立一個名為GsonTester的Java類檔案:GsonTester.java -

import java.lang.reflect.Type; 

import com.google.gson.Gson; 
import com.google.gson.reflect.TypeToken;  

public class GsonTester { 
   public static void main(String args[]) { 
      // create a shape class of type circle. 
      Shape<Circle> shape = new Shape<Circle>();  

      // Create a Circle object 
      Circle circle = new Circle(5.0);  

      //assign circle to shape 
      shape.setShape(circle);  
      Gson gson = new Gson(); 

      // Define a Type shapeType of type circle. 
      Type shapeType = new TypeToken<Shape<Circle>>() {}.getType();  

      //Serialize the json as ShapeType 
      String jsonString = gson.toJson(shape, shapeType); 
      System.out.println(jsonString);  
      Shape shape1 = gson.fromJson(jsonString, Shape.class); 

      System.out.println(shape1.get().getClass()); 
      System.out.println(shape1.get().toString()); 
      System.out.println(shape1.getArea());  
      Shape shape2 = gson.fromJson(jsonString, shapeType); 
      System.out.println(shape2.get().getClass()); 
      System.out.println(shape2.get().toString()); 
      System.out.println(shape2.getArea()); 
   }      
}  
class Shape <T> { 
   public T shape;  

   public void setShape(T shape) { 
      this.shape = shape; 
   }  
   public T get() { 
      return shape; 
   }  
   public double getArea() { 
      if(shape instanceof Circle) { 
         return ((Circle) shape).getArea(); 
      } else { 
         return 0.0; 
      } 
   } 
}  
class Circle { 
   private double radius;  

   public Circle(double radius){ 
      this.radius = radius; 
   }  
   public String toString() { 
      return "Circle"; 
   }  
   public double getRadius() { 
      return radius; 
   }  
   public void setRadius(double radius) { 
      this.radius = radius; 
   }  
   public double getArea() { 
      return (radius*radius*3.14); 
   } 
}

執行上面範例程式碼，得到以下結果 -

{"shape":{"radius":5.0}} 
class com.google.gson.internal.LinkedTreeMap 
{radius = 5.0} 
0.0 
class Circle 
Circle 
78.5