如何在Java中使用JSON文件的输出来创建对象？

Question

我不得不为学校的一个项目用Java编写了一个小游戏。这个游戏是RushHour，你可以在这里看到一个例子：http://www.thinkfun.com/play-online/rush-hour/。

我的老师现在要求我允许我的代码读取外部文件，这样游戏的初始状态就不再是硬编码在我的main中，并且游戏的参数可以自定义(棋盘的大小，游戏中的汽车数量……)

这是我的第一个JSON文件，它设置了一个经典游戏。

{
"ClassicBoard" :
        {
            "height" : "6",
            "width"  : "6",
             "exit":
                 {
                   "row" : "2",
                   "column" : "5"
                 }
        },
"ListOfCars" :
        {
            "car2" :
                {
                   "char" : "2",
                   "size" : "3",
                   "orientation" : "vertical",
                   "currentPosition":
                            {
                             "row" : "2",
                             "column": "2"
                            }
                },            
            "car3"  :
                {
                "char" : "3",
                "size" : "3",
                "orientation" : "vertical",
                "currentPosition":
                            {
                             "row" : "2",
                             "column": "4"
                            }
                }
        },
"redCar":
        {
         "char" : "1",
         "size" : "2",
         "orientation" : "horizontal",
         "currentPosition":
            {
              "row" : "2",
              "column": "0"
            }
        }

}

我正在尝试找到如何读取文件并重用它的输出来创建一个RushHourGame对象。这是构造函数。

public RushHourGame(Board board, List <Car> cars, Car redCar) throws RushHourException
{
    this.board = board;
    this.redCar = redCar;

    if(((redCar.getOrientation() == Orientation.HORIZONTAL)
            && (board.getExit().getRow() != redCar.getCurrentPosition().getRow()))
            || (((redCar.getOrientation() == Orientation.VERTICAL)
            && (board.getExit().getColumn() != redCar.getCurrentPosition().getColumn()))))
    {
        throw new RushHourException("Car must be aligned with the exit, "
                + "a default game has been created");
    }
    board.put(redCar);
    for (Car putCars : cars)
    {
        board.put(putCars);
    }
}

我试着使用BufferedReader，就像这样。

public static String readFile(String filename)
{
    String result ="";
    try
    {
        BufferedReader br = new BufferedReader (new FileReader(filename));
        StringBuilder sb = new StringBuilder();
        String line = br.readLine();
        while (line != null)
        {
            sb.append(line);
            line = br.readLine();
        }
        result = sb.toString();
    }
    catch (Exception e)
    {
        e.printStackTrace();
    }
    return result;
}

但是我不知道如何使用它来解析我的JSON文件。有人能帮帮我吗？

Answer 1

你的问题的多个答案可以在here上找到。我更喜欢StaxMan提供的答案：

最简单的选项是Jackson

MyObject ob = new ObjectMapper().readValue(jsonString, RushHourState.class);

上面的代码应该会使用下面提供的Java POJO自动处理JSON/Java对象绑定：

public class RushHourState {
   private ArrayList<Car> listOfCars;
   private ClassicBoard classicBoard;
   private Car redCar;

   public ArrayList<Car> getListOfCars() {
       return listOfCars;
   }
   public void setListOfCars(ArrayList<Car> listOfCars) {
       this.listOfCars = listOfCars;
   }
   public ClassicBoard getClassicBoard() {
       return classicBoard;
   }
   public void setClassicBoard(ClassicBoard classicBoard) {
       this.classicBoard = classicBoard;
   }
   public Car getRedCar() {
       return redCar;
   }
   public void setRedCar(Car redCar) {
       this.redCar = redCar;
   }
}

// ---------------------------------------------------

public class ClassicBoard {
   private int height;
   private int width;
   private HashMap<String, String> exit;
   public int getHeight() {
    return height;
   }
   public void setHeight(int height) {
    this.height = height;
   }
   public int getWidth() {
    return width;
   }
   public void setWidth(int width) {
    this.width = width;
   }
   public HashMap<String, String> getExit() {
    return exit;
   }
   public void setExit(HashMap<String, String> exit) {
    this.exit = exit;
   }
}

// ---------------------------------------------------

public class Car {
    private int charr;
    private int size;
    private String orientation;
    private HashMap<String, String> currentPosition;
    public int getCharr() {
        return charr;
    }
    public void setCharr(int charr) {
        this.charr = charr;
    }
    public int getSize() {
        return size;
    }
    public void setSize(int size) {
        this.size = size;
    }
    public String getOrientation() {
        return orientation;
    }
    public void setOrientation(String orientation) {
        this.orientation = orientation;
    }
    public HashMap<String, String> getCurrentPosition() {
        return currentPosition;
    }
    public void setCurrentPosition(HashMap<String, String> currentPosition) {
        this.currentPosition = currentPosition;
    }
}

注意:我将Car类中的变量' char‘重命名为'charr’，因为char是一个Java保留关键字。希望这篇文章对你有帮助！