从元素列表中的 json 加载

Question

我需要将这个 king json 文件加载到 Java 中的某个对象中。

[
    {
        "id": 1,
        "name": "FA1_M",
        "ring_number": 1,
        "type": 3,
        "unit_index": 1,
        "device_type": 3,
        "address": 1,
        "index_ring": 1,
        "order": 0
    },
    {
        "id": 2,
        "name": "A1_1_LED",
        "ring_number": 1,
        "type": 4,
        "unit_index": 1,
        "device_type": 3,
        "address": 1,
        "index_ring": 2,
        "order": 1
    },
    {
        "id": 3,
        "name": "FA1_A",
        "ring_number": 1,
        "type": 3,
        "unit_index": 1,
        "device_type": 3,
        "address": 2,
        "index_ring": 3,
        "order": 2
    },
    {
        "id": 4,
        "name": "A1_2_LED",
        "ring_number": 1,
        "type": 4,
        "unit_index": 1,
        "device_type": 3,
        "address": 2,
        "index_ring": 4,
        "order": 3
    },
    {
        "id": 5,
        "name": "FA1_BMA",
        "ring_number": 1,
        "type": 3,
        "unit_index": 1,
        "device_type": 3,
        "address": 3,
        "index_ring": 5,
        "order": 4
    },
    {
        "id": 6,
        "name": "A1_3_LED",
        "ring_number": 1,
        "type": 4,
        "unit_index": 1,
        "device_type": 3,
        "address": 3,
        "index_ring": 6,
        "order": 5
    },
    {
        "id": 7,
        "name": "Reserve_IN_4",
        "ring_number": 1,
        "type": 3,
        "unit_index": 1,
        "device_type": 3,
        "address": 4,
        "index_ring": 7,
        "order": 6
    },
    {
        "id": 8,
        "name": "A1_4_LED",
        "ring_number": 1,
        "type": 4,
        "unit_index": 1,
        "device_type": 3,
        "address": 4,
        "index_ring": 8,
        "order": 7
    },
    {
        "id": 9,
        "name": "Reserve_IN_5",
        "ring_number": 1,
        "type": 3,
        "unit_index": 1,
        "device_type": 3,
        "address": 5,
        "index_ring": 9,
        "order": 8
    },
    {
        "id": 10,
        "name": "A1_5_LED",
        "ring_number": 1,
        "type": 4,
        "unit_index": 1,
        "device_type": 3,
        "address": 5,
        "index_ring": 10,
        "order": 9
    },
    {
        "id": 11,
        "name": "Reserve_IN_6",
        "ring_number": 1,
        "type": 3,
        "unit_index": 1,
        "device_type": 3,
        "address": 6,
        "index_ring": 11,
        "order": 10
    },
    {
        "id": 12,
        "name": "Reserve_OUT_6",
        "ring_number": 1,
        "type": 4,
        "unit_index": 1,
        "device_type": 3,
        "address": 6,
        "index_ring": 12,
        "order": 11
    },
    {
        "id": 13,
        "name": "Reserve_IN_7",
        "ring_number": 1,
        "type": 3,
        "unit_index": 1,
        "device_type": 3,
        "address": 7,
        "index_ring": 13,
        "order": 12
    },
    {
        "id": 14,
        "name": "KK1_ENB",
        "ring_number": 1,
        "type": 4,
        "unit_index": 1,
        "device_type": 3,
        "address": 7,
        "index_ring": 14,
        "order": 13
    },
    {
        "id": 15,
        "name": "FA2_BMA",
        "ring_number": 1,
        "type": 3,
        "unit_index": 1,
        "device_type": 3,
        "address": 8,
        "index_ring": 15,
        "order": 14
    },
    {
        "id": 16,
        "name": "KK2_ENB",
        "ring_number": 1,
        "type": 4,
        "unit_index": 1,
        "device_type": 3,
        "address": 8,
        "index_ring": 16,
        "order": 15
    },
    {
        "id": 17,
        "name": "Smoke1_1",
        "ring_number": 1,
        "type": 2,
        "unit_index": 2,
        "device_type": 2,
        "address": 1,
        "index_ring": 17,
        "order": 16
    },
    {
        "id": 18,
        "name": "Smoke1_2",
        "ring_number": 1,
        "type": 2,
        "unit_index": 3,
        "device_type": 12,
        "address": 1,
        "index_ring": 18,
        "order": 17
    },
    {
        "id": 19,
        "name": "Smoke1_3",
        "ring_number": 1,
        "type": 2,
        "unit_index": 4,
        "device_type": 2,
        "address": 1,
        "index_ring": 19,
        "order": 18
    },
    {
        "id": 20,
        "name": "Smoke1_4",
        "ring_number": 1,
        "type": 2,
        "unit_index": 5,
        "device_type": 2,
        "address": 1,
        "index_ring": 20,
        "order": 19
    },
    {
        "id": 21,
        "name": "Fire1_1",
        "ring_number": 1,
        "type": 1,
        "unit_index": 6,
        "device_type": 4,
        "address": 1,
        "index_ring": 21,
        "order": 20
    },
    {
        "id": 22,
        "name": "Fire1_2",
        "ring_number": 1,
        "type": 1,
        "unit_index": 6,
        "device_type": 4,
        "address": 2,
        "index_ring": 22,
        "order": 21
    },
    {
        "id": 23,
        "name": "Fire1_3",
        "ring_number": 1,
        "type": 1,
        "unit_index": 7,
        "device_type": 1,
        "address": 1,
        "index_ring": 23,
        "order": 22
    },
    {
        "id": 24,
        "name": "Motorless1",
        "ring_number": 1,
        "type": 5,
        "unit_index": 8,
        "device_type": 13,
        "address": 1,
        "index_ring": 24,
        "order": 23
    },
    {
        "id": 25,
        "name": "Fire1_4",
        "ring_number": 1,
        "type": 1,
        "unit_index": 9,
        "device_type": 14,
        "address": 1,
        "index_ring": 25,
        "order": 24
    },
    {
        "id": 26,
        "name": "Fire1_5",
        "ring_number": 1,
        "type": 1,
        "unit_index": 9,
        "device_type": 14,
        "address": 2,
        "index_ring": 26,
        "order": 25
    }
]

我有类 Element 描述一个元素

public class element {
    protected int id;
    protected int type;
    protected String state;
    protected int status;
    protected int device_type;
    private Map<String, Integer>mask;


    public int getId(){return this.id;}
    public void setId(int id){this.id=id;}
    public int getType(){return this.type;}
    public void setType(int type){this.type=type;}
    public String getState(){return this.state;}
    public void setState(String state){this.state=state;}
    public int getStatus(){return this.status;}
    public void setStatus(int status){this.status=status;}
    public int getDeviceType(){return this.device_type;}
    public void setDeviceType(int device_type){this.device_type=device_type;}
    public Map<String,Integer> getMask(){return this.mask;}
    public void setMask(Map<String,Integer> mask){this.mask=mask;}

    //index start by 1, not 0
    public boolean getBit(int index){
        return ((this.status>>(index-1)) & 0x1)==1;
    }

    public ElementView generateView(){
        return null;
    }

}

如何在元素列表中加载 json？我用 GSON 查看了 stackoverflow 问题，但是需要在 json 中为这个数组指定一些名称，但我没有。有人可以帮忙吗？

Answer 1

您需要指定元素类型/类。例如，你有下面的数组 json
[{"id":"01","name":"Joe"},{"id":"02","name":"Doe"}]

您必须创建学生班级

public class Student {
    private String id;
    private  String name;

    public Student() {

    }

    public Student(String id, String name) {
        super();
        this.id = id;
        this.name = name;
    }

    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Student [id=" + id + ", name=" + name + "]";
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((id == null) ? 0 : id.hashCode());
        result = prime * result + ((name == null) ? 0 : name.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Student other = (Student) obj;
        if (id == null) {
            if (other.id != null)
                return false;
        } else if (!id.equals(other.id))
            return false;
        if (name == null) {
            if (other.name != null)
                return false;
        } else if (!name.equals(other.name))
            return false;
        return true;
    }

}

之后需要指定集合类型，并访问fromJson方法

Type collectionType = new TypeToken<List<Student>>(){}.getType();
List<Student> students = gson.fromJson(json, collectionType);

整个测试代码如下

public class When_serialize_list_object {
    private List<Student> _students;
    private Gson gson = new Gson();

    @Before
    public void setUp() {
        _students = new ArrayList<Student>();

        Student student1 = new Student("01", "Joe");
        Student student2 = new Student("02", "Doe");

        _students.add(student1);
        _students.add(student2);
    }

    @Test
    public void should_able_to_deserialize() {      
        String json = gson.toJson(_students);

        System.out.println(json);
        Type collectionType = new TypeToken<List<Student>>(){}.getType();
        List<Student> students = gson.fromJson(json, collectionType);

        Assert.assertEquals(students, _students);
        System.out.println(students);
    }

}

Answer 2

例如，使用 JSON-Simple 库

  Object obj=JSONValue.parse(jsonString);
  JSONArray array=(JSONArray)obj;
  JSONObject element0=(JSONObject)array.get(0);

  Element el = new Element();
  el.setId( element0.get("id") );
  ...

Answer 3

看看杰克逊。它在解析 JSON 方面比 GSON 更有效。我通常先伟大我的对象，然后使用 Jackson 将其发送到 Json 字符串，这样我就知道我的 Json 字符串需要是什么样子。这是一个示例：

User user = new User();
        user.setFirstName("Kmb");
        ....
        UserStatus userStatus = new UserStatus();
        userStatus.setKey("1");
        userStatus.setKey("active");
        user.setUserStatus(userStatus);

        String strUser="";
        try {
            strUser =mapper.writeValueAsString(user);
        } catch (JsonGenerationException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (JsonMappingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
       System.out.println(strUser);

一旦您了解了字符串应如何格式化，请调整您的输入以匹配 Jackson 想要的格式。然后将字符串与您的类一起传递到映射器中。

try {
        String str; //your string here
           User user2 = mapper.readValue(str, User.class);
           System.out.println(user2.getFirstName());
           System.out.println(user2.getServiceType().getValue());

        } catch (JsonParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (JsonMappingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

如果您想要一个元素数组，您可能需要创建一个简单的类来包装元素列表并通过 Jackson 运行它。

  <dependencies>
    <dependency>
        <groupId>org.codehaus.jackson</groupId>
        <artifactId>jackson-mapper-asl</artifactId>
        <version>1.7.5</version>
        <type>jar</type>
        <scope>compile</scope>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.8.2</version>
        <type>jar</type>
        <scope>compile</scope>
    </dependency>
    <dependency>
        <groupId>org.codehaus.jackson</groupId>
        <artifactId>jackson-core-asl</artifactId>
        <version>1.7.5</version>
        <type>jar</type>
        <scope>compile</scope>
    </dependency>
  </dependencies>