Jackson 使用和注意项

依赖maven:

   <dependency>

            <groupId>com.fasterxml.jackson.core</groupId>

            <artifactId>jackson-databind</artifactId>

            <version>2.6.5</version>

        </dependency>

        <dependency>

            <groupId>com.fasterxml.jackson.core</groupId>

            <artifactId>jackson-core</artifactId>

            <version>2.6.5</version>

        </dependency>

        <dependency>

            <groupId>com.fasterxml.jackson.core</groupId>

            <artifactId>jackson-annotations</artifactId>

            <version>2.6.5</version>

        </dependency>

code:

User:

import lombok.*;

@Data

@ToString

@NoArgsConstructor

@AllArgsConstructor

public class User {

    private int id;

    private String name;

    private String email;

    private String address;

    private Birthday birthday;

}

Birthday:

import lombok.*;

@Data

@ToString

@NoArgsConstructor

@AllArgsConstructor

public class Birthday {

    private String birthday;

}

User2:

import lombok.AllArgsConstructor;

import lombok.Data;

import lombok.NoArgsConstructor;

import lombok.ToString;

@Data

@ToString

@NoArgsConstructor

@AllArgsConstructor

public class User2 {

    private int id;

    private String name;

    private String email;

//    private String address;

//    private Birthday birthday;

}

1.查看基础类型的序列化与反序列化：

import com.fasterxml.jackson.databind.ObjectMapper;

import lombok.val;

import java.io.IOException;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

public class test{

    private final static ObjectMapper objectMapper = new ObjectMapper();

    public static void main(String[] args) {

        User user = new User();

        user.setAddress("asdf");

        user.setAddress("中国河南省");

        user.setEmail("xiaokui_wingfly@sina.com.cn");

        user.setId(1);

        user.setName("X-rapido");

        user.setBirthday(new Birthday("2015-08-06"));

        List<String> list = new ArrayList<String>();

        list.add("a");

        list.add("b");

        list.add("c");

        Map<String, Object> map = new HashMap<String, Object>();

        map.put("a", "1");

        map.put("b", "2");

        map.put("c", "3");

        map.put("list", list);

        String []sz = {"a","b","c"};

        try {

            System.out.println(objectMapper.writeValueAsString(user));

            System.out.println(objectMapper.writeValueAsString(list));

            System.out.println(objectMapper.writeValueAsString(map));

            System.out.println(objectMapper.writeValueAsString(sz));

            String s = "{\"name\":\"X-rapido\"}";

            // Json转换JavaBean

            User a = objectMapper.readValue(s, User.class);

            System.out.println(a.getName());

            // JavaBean转换Json

            System.out.println(objectMapper.writeValueAsString(a));

        } catch (IOException e) {

            e.printStackTrace();

        }

    }

}

Output:

{"id":1,"name":"X-rapido","email":"xiaokui_wingfly@sina.com.cn","address":"中国河南省","birthday":{"birthday":"2015-08-06"}}

["a","b","c"]

{"a":"1","b":"2","c":"3","list":["a","b","c"]}

["a","b","c"]

X-rapido

{"id":0,"name":"X-rapido","email":null,"address":null,"birthday":null}

2.有这么种情况，就是字符串反序列化为对象，但是字符串中的很多字段我都不需要，只需要一部分，这个时候怎么反序列化：

import com.fasterxml.jackson.databind.DeserializationFeature;

import com.fasterxml.jackson.databind.ObjectMapper;

import lombok.val;

import java.io.IOException;

public class test{

    private final static ObjectMapper objectMapper = new ObjectMapper();

    public static void main(String[] args) {

        //当反序列化json时，未知属性会引起的反序列化被打断，这里我们禁用未知属性打断反序列化功能，

        //因为，例如json里有10个属性，而我们的bean中只定义了2个属性，其它8个属性将被忽略

        objectMapper .disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);

        User user = new User();

        user.setAddress("asdf");

        user.setAddress("中国河南省");

        user.setEmail("xiaokui_wingfly@sina.com.cn");

        user.setId(1);

        user.setName("X-rapido");

        user.setBirthday(new Birthday("2015-08-06"));

        try {

            System.out.println("========begin=======");

            val content=objectMapper.writeValueAsString(user);

            System.out.println(content);

            User2 u=objectMapper.readValue(content,User2.class);

            System.out.println(objectMapper.writeValueAsString(u));

            System.out.println("========end=======");

        } catch (IOException e) {

            e.printStackTrace();

        }

    }

}

Output:

========begin=======

{"id":1,"name":"X-rapido","email":"xiaokui_wingfly@sina.com.cn","address":"中国河南省","birthday":{"birthday":"2015-08-06"}}

{"id":1,"name":"X-rapido","email":"xiaokui_wingfly@sina.com.cn"}

========end=======

注意：

        objectMapper .disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);

如果不加这个会报错：

========begin=======

{"id":1,"name":"X-rapido","email":"xiaokui_wingfly@sina.com.cn","address":"中国河南省","birthday":{"birthday":"2015-08-06"}}

com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "address" (class com.qhong.json.User2), not marked as ignorable (3 known properties: "id", "email", "name"])

 at [Source: {"id":1,"name":"X-rapido","email":"xiaokui_wingfly@sina.com.cn","address":"中国河南省","birthday":{"birthday":"2015-08-06"}}; line: 1, column: 76] (through reference chain: com.qhong.json.User2["address"])

    at com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException.from(UnrecognizedPropertyException.java:51)

    at com.fasterxml.jackson.databind.DeserializationContext.reportUnknownProperty(DeserializationContext.java:839)

    at com.fasterxml.jackson.databind.deser.std.StdDeserializer.handleUnknownProperty(StdDeserializer.java:1045)

    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownProperty(BeanDeserializerBase.java:1352)

    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownVanilla(BeanDeserializerBase.java:1330)

    at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:264)

    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:125)

    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3736)

    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2726)

    at com.qhong.json.test.main(test.java:29)

3.怎么反序列化对象数组：

import com.fasterxml.jackson.databind.DeserializationFeature;

import com.fasterxml.jackson.databind.ObjectMapper;

import lombok.val;

import java.io.IOException;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.List;

public class test{

    private final static ObjectMapper objectMapper = new ObjectMapper();

    public static void main(String[] args) {

        //当反序列化json时，未知属性会引起的反序列化被打断，这里我们禁用未知属性打断反序列化功能，

        //因为，例如json里有10个属性，而我们的bean中只定义了2个属性，其它8个属性将被忽略

        objectMapper .disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);

        List<User> arr= Arrays.asList(

                    new User(1, "name1", "email1", "address1", new Birthday("2016-08-01")),

                    new User(2 ,"name2", "email2", "address2", new Birthday("2016-08-02")),

                    new User(3, "name3", "email3", "address3", new Birthday("2016-08-03"))

        );

        try {

            System.out.println("========begin=======");

            val content=objectMapper.writeValueAsString(arr);

            System.out.println(content);

            List<User> list=objectMapper.readValue(content,new com.fasterxml.jackson.core.type.TypeReference<List<User>>(){});

            System.out.println(objectMapper.writeValueAsString(list));

            System.out.println("另外的方式：");

           // List<MyClass> myObjects = mapper.readValue(jsonInput, mapper.getTypeFactory().constructCollectionType(List.class, MyClass.class));

            List<User> list2=objectMapper.readValue(content,objectMapper.getTypeFactory().constructCollectionType(ArrayList.class,User.class));

            System.out.println(objectMapper.writeValueAsString(list2));

            System.out.println("========end=======");

        } catch (IOException e) {

            e.printStackTrace();

        }

    }

}

Output:

========begin=======

[{"id":1,"name":"name1","email":"email1","address":"address1","birthday":{"birthday":"2016-08-01"}},{"id":2,"name":"name2","email":"email2","address":"address2","birthday":{"birthday":"2016-08-02"}},{"id":3,"name":"name3","email":"email3","address":"address3","birthday":{"birthday":"2016-08-03"}}]

[{"id":1,"name":"name1","email":"email1","address":"address1","birthday":{"birthday":"2016-08-01"}},{"id":2,"name":"name2","email":"email2","address":"address2","birthday":{"birthday":"2016-08-02"}},{"id":3,"name":"name3","email":"email3","address":"address3","birthday":{"birthday":"2016-08-03"}}]

另外的方式：

[{"id":1,"name":"name1","email":"email1","address":"address1","birthday":{"birthday":"2016-08-01"}},{"id":2,"name":"name2","email":"email2","address":"address2","birthday":{"birthday":"2016-08-02"}},{"id":3,"name":"name3","email":"email3","address":"address3","birthday":{"birthday":"2016-08-03"}}]

========end=======

还有一些其他的特殊情况，比如json对象key没有双引号等

import com.fasterxml.jackson.annotation.JsonInclude;

import com.fasterxml.jackson.core.JsonGenerator;

import com.fasterxml.jackson.core.JsonParser;

import com.fasterxml.jackson.core.type.TypeReference;

import com.fasterxml.jackson.databind.DeserializationFeature;

import com.fasterxml.jackson.databind.ObjectMapper;

import com.fasterxml.jackson.databind.SerializationFeature;

import lombok.AllArgsConstructor;

import lombok.Data;

import lombok.NoArgsConstructor;

import lombok.ToString;

import java.util.List;

public class test2{

    private final static  ObjectMapper mapper= new ObjectMapper();

        public static void main(String[] args) {

          try {

              mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);

              // 如果为空则不输出

              mapper.setSerializationInclusion(JsonInclude.Include.NON_EMPTY);

              // 对于空的对象转json的时候不抛出错误

              mapper.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS);

              // 禁用序列化日期为timestamps

              mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);

              // 禁用遇到未知属性抛出异常

              mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);

              // 视空字符传为null

              mapper.enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);

              // 低层级配置

              mapper.configure(JsonParser.Feature.ALLOW_COMMENTS, true);

              // 允许属性名称没有引号

              mapper.configure(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES, true);

              // 允许单引号

              mapper.configure(JsonParser.Feature.ALLOW_SINGLE_QUOTES, true);

              // 取消对非ASCII字符的转码

              mapper.configure(JsonGenerator.Feature.ESCAPE_NON_ASCII, false);

              //mapper.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS);

              String str = " [\n" +

                      "    {\n" +

                      "        \"symbol\": \"sh603111\", \n" +

                      "        \"code\": \"603111\", \n" +

                      "        \"name\": \"康尼机电\", \n" +

                      "        \"trade\": \"14.530\", \n" +

                      "        \"pricechange\": \"0.770\", \n" +

                      "        \"changepercent\": \"5.596\", \n" +

                      "        \"buy\": \"14.530\", \n" +

                      "        \"sell\": \"14.540\", \n" +

                      "        \"settlement\": \"13.760\", \n" +

                      "        \"open\": \"13.820\", \n" +

                      "        \"high\": \"14.540\", \n" +

                      "        \"low\": \"13.820\", \n" +

                      "        \"volume\": 18591408, \n" +

                      "        \"amount\": 266138177, \n" +

                      "        \"ticktime\": \"15:00:00\", \n" +

                      "        \"per\": 44.339, \n" +

                      "        \"pb\": 7.731, \n" +

                      "        \"mktcap\": 1072870.86225, \n" +

                      "        \"nmc\": 697004.688465, \n" +

                      "        \"turnoverratio\": 3.87563\n" +

                      "    }, \n" +

                      "    {\n" +

                      "        \"symbol\": \"sz300355\", \n" +

                      "        \"code\": \"300355\", \n" +

                      "        \"name\": \"蒙草生态\", \n" +

                      "        \"trade\": \"12.330\", \n" +

                      "        \"pricechange\": \"0.620\", \n" +

                      "        \"changepercent\": \"5.295\", \n" +

                      "        \"buy\": \"12.330\", \n" +

                      "        \"sell\": \"12.340\", \n" +

                      "        \"settlement\": \"11.710\", \n" +

                      "        \"open\": \"11.640\", \n" +

                      "        \"high\": \"12.580\", \n" +

                      "        \"low\": \"11.640\", \n" +

                      "        \"volume\": 142839605, \n" +

                      "        \"amount\": 1741652819, \n" +

                      "        \"ticktime\": \"15:06:03\", \n" +

                      "        \"per\": 35.229, \n" +

                      "        \"pb\": 6.27, \n" +

                      "        \"mktcap\": 1978030.485873, \n" +

                      "        \"nmc\": 1428385.32288, \n" +

                      "        \"turnoverratio\": 12.33009\n" +

                      "    }\n" +

                      "]";

              System.out.println(str);

              List<riseInfo> list = mapper.readValue(str, new TypeReference<List<riseInfo>>() {

              });

              System.out.println(list.size());

          }catch (Exception ex){

              System.out.println(ex.getMessage());

              System.out.println(ex.getStackTrace());

          }

        }

}

@Data

@ToString

@NoArgsConstructor

@AllArgsConstructor

class riseInfo {

    private String symbol;

    private String code;

    private String name;

}

Output:

 [

    {

        "symbol": "sh603111",

        "code": "",

        "name": "康尼机电",

        "trade": "14.530",

        "pricechange": "0.770",

        "changepercent": "5.596",

        "buy": "14.530",

        "sell": "14.540",

        "settlement": "13.760",

        "open": "13.820",

        "high": "14.540",

        "low": "13.820",

        "volume": ,

        "amount": ,

        "ticktime": "15:00:00",

        "per": 44.339,

        "pb": 7.731,

        "mktcap": 1072870.86225,

        "nmc": 697004.688465,

        "turnoverratio": 3.87563

    },

    {

        "symbol": "sz300355",

        "code": "",

        "name": "蒙草生态",

        "trade": "12.330",

        "pricechange": "0.620",

        "changepercent": "5.295",

        "buy": "12.330",

        "sell": "12.340",

        "settlement": "11.710",

        "open": "11.640",

        "high": "12.580",

        "low": "11.640",

        "volume": ,

        "amount": ,

        "ticktime": "15:06:03",

        "per": 35.229,

        "pb": 6.27,

        "mktcap": 1978030.485873,

        "nmc": 1428385.32288,

        "turnoverratio": 12.33009

    }

]

添加配置即可！

http://blog.csdn.net/langzi7758521/article/details/52072457

http://www.cnblogs.com/kakag/p/5054772.html

http://www.cnblogs.com/dupang/p/5673097.html

https://codeday.me/bug/20170221/3548.html

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