Json工具Demo(二)

上篇文章Json工具Demo(一) 说了一些Json和Jackson框架的基本知识，以及Demo中需要用到的基本类。这篇文章主要写下json和java对象之间相互转换的工具类JacksonUtil.java和测试类Main.java。

如果是List<User>或者Map<String, User>使用toJsonWithRoot方法转换成json串，当用jsonToBeanByTypeReferenceWithRoot方法转换成Java Bean时，会导致该Bean为null。因此，需要使用一个新的类，如UserList或者UserMap类来实现，就可以避免这个问题。

使用下面的代码需要的依赖是：

<dependency><groupId>com.fasterxml.jackson.core</groupId><artifactId>jackson-core</artifactId><version>2.8.5</version></dependency><dependency><groupId>com.fasterxml.jackson.core</groupId><artifactId>jackson-databind</artifactId><version>2.8.5</version></dependency><dependency><groupId>com.fasterxml.jackson.core</groupId><artifactId>jackson-annotations</artifactId><version>2.8.5</version></dependency>

JacksonUtil

JacksonUtil.java

package org.fan.learn.utils;import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.*;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;import java.io.IOException;
import java.util.Locale;
import java.util.Map;/*** Created by fan on 15-11-18.*/
public class JacksonUtil {private static final Logger LOGGER = LoggerFactory.getLogger(JacksonUtil.class);private static ObjectMapper mapper;public static synchronized ObjectMapper getMapperInstance(boolean createNew) {if (createNew) {return new ObjectMapper();} else if (mapper == null) {mapper = new ObjectMapper();//对象属性按字母顺序排列mapper.configure(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY, true);//在反序列化时，如果类中没有对应的属性，不抛出JsonMappingException异常mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);//序列化时，如果对象的某属性为null,生成Json字符串时不包含这个null属性mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);mapper.setLocale(Locale.CHINA);}return mapper;}/*** 将java对象转换为字符串* @param param java 对象* @return json字符串*/public static String toJson(Object param){try {ObjectMapper objectMapper = JacksonUtil.getMapperInstance(false);objectMapper.configure(SerializationFeature.WRAP_ROOT_VALUE, false);String dataJson =  objectMapper.writeValueAsString(param);return dataJson;}catch (Exception e){LOGGER.warn("toJson",e);}return null;}/*** 将java对象为字符串 类名作为json的顶级属性* @param param java 对象* @returnjson字符串*/public static String toJsonWithRoot(Object param){try {ObjectMapper objectMapper = JacksonUtil.getMapperInstance(false);objectMapper.configure(SerializationFeature.WRAP_ROOT_VALUE, true);String dataJson =  objectMapper.writeValueAsString(param);return dataJson;}catch (Exception e){LOGGER.warn("toJson",e);}return null;}/*** 将json字符串转换为java对象* @param json json字符串* @param cls java对象类型* @param <T>* @return*/public static <T> T jsonToBean(String json, Class<T> cls){try {ObjectMapper objectMapper = JacksonUtil.getMapperInstance(false);objectMapper.configure(DeserializationFeature.UNWRAP_ROOT_VALUE,false);return objectMapper.readValue(json, cls);} catch (Exception e) {LOGGER.warn("jsonToBean",e);return null;}}/*** 将json字符串转换为java对象  ，解析字符串时，将类的名字或者别名作为顶级属性来解析* @param json json字符串* @param cls java对象类型* @param <T>* @return*/public static <T> T jsonToBeanWithRoot(String json, Class<T> cls){try {ObjectMapper objectMapper = JacksonUtil.getMapperInstance(false);objectMapper.configure(DeserializationFeature.UNWRAP_ROOT_VALUE, true);return objectMapper.readValue(json, cls);} catch (Exception e) {LOGGER.warn("jsonToBean",e);return null;}}/*** 将json字符串转换为java对象* @param json json字符串* @param typeReference 复杂的java对象类型* @param <T>* @return*/public static <T> T jsonToBeanByTypeReference(String json, TypeReference typeReference){try {ObjectMapper objectMapper = JacksonUtil.getMapperInstance(false);objectMapper.configure(DeserializationFeature.UNWRAP_ROOT_VALUE,false);return objectMapper.readValue(json, typeReference);} catch (Exception e) {LOGGER.warn("jsonToBean",e);return null;}}/*** 将json字符串转换为java对象，解析字符串时，将类的名字或者别名作为顶级属性来解析* @param json json字符串* @param typeReference 复杂的java对象类型* @param <T>* @return*/public static <T> T jsonToBeanByTypeReferenceWithRoot(String json, TypeReference typeReference){try {ObjectMapper objectMapper = JacksonUtil.getMapperInstance(false);objectMapper.configure(DeserializationFeature.UNWRAP_ROOT_VALUE,true);return objectMapper.readValue(json, typeReference);} catch (Exception e) {LOGGER.warn("jsonToBean",e);return null;}}/*** 从json字符串中读取出指定的节点** @param json* @param key* @return* @throws JsonProcessingException* @throws IOException*/public static JsonNode getValueFromJson(String json, String key) {ObjectMapper objectMapper = JacksonUtil.getMapperInstance(false);objectMapper.configure(DeserializationFeature.UNWRAP_ROOT_VALUE,false);JsonNode node = null;try {node = objectMapper.readTree(json);return node.get(key);} catch (IOException e) {LOGGER.warn("getValueFromJson",e);return null;}}
}

Main测试

package org.fan.learn.json;import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.JsonNode;
import com.google.common.collect.Lists;
import com.google.common.collect.Maps;
import org.fan.learn.utils.JacksonUtil;import java.util.List;
import java.util.Map;/*** Created by fan on 15-11-18.*/
public class Main {public static void main(String[] args) {List<User> userList = Lists.newArrayList();String[] phone = {"15888888888", "15222222222"};Birthday birthday = new Birthday(2000,8,8);User user = new User("宝宝", -26, phone, birthday, true);User user1 = new User("fan", 25, phone, birthday, false);
/*        User user = new User();user.setName("fan");user.setAge(26);User user1 = new User();user1.setName("li");user1.setAge(25);*/userList.add(user);userList.add(user1);Map<String, User> userMap = Maps.newHashMap();userMap.put("user1", user);userMap.put("user2", user1);//会调用get方法String userString = JacksonUtil.toJson(user);//会调用无参构造函数,set方法User userJson = JacksonUtil.jsonToBean(userString, User.class);Map<String,String> userJsonMap = JacksonUtil.jsonToBean(userString, Map.class);System.out.println(userJsonMap);JsonNode name = JacksonUtil.getValueFromJson(userString, "NAME");JsonNode age = JacksonUtil.getValueFromJson(userString, "AGE");JsonNode phoneNode = JacksonUtil.getValueFromJson(userString, "PHONE");JsonNode birthdayNode = JacksonUtil.getValueFromJson(userString, "BIRTHDAY");JsonNode maleNode = JacksonUtil.getValueFromJson(userString, "MALE");String nameStr = name.toString();int ageInt = age.intValue();//List<String> phoneArr = phoneNode.findValuesAsText("PHONE");String[] phoneArr = new String[phoneNode.size()];for (int i = 0; i < phoneNode.size(); i++) {phoneArr[i] = phoneNode.get(i).toString();}Birthday birthdayObj = new Birthday();//会分别调用Birthday的3个setter方法birthdayObj.setYear(birthdayNode.get("year").intValue());birthdayObj.setMonth(birthdayNode.get("month").intValue());birthdayObj.setDay(birthdayNode.get("day").intValue());boolean male = maleNode.booleanValue();String userString2 = JacksonUtil.toJsonWithRoot(user);//使用这种内部数据将会是nullUser userJson2_1 = JacksonUtil.jsonToBean(userString2, User.class);User userJson2_2 = JacksonUtil.jsonToBeanWithRoot(userString2, User.class);String userListString = JacksonUtil.toJson(userList);List<User> userListJson = JacksonUtil.jsonToBeanByTypeReference(userListString,new TypeReference<List<User>>(){});String userListStringRoot = JacksonUtil.toJsonWithRoot(userList);//这种使用方法，得到的userListJsonRoot是nullList<User> userListJsonRoot = JacksonUtil.jsonToBeanByTypeReferenceWithRoot(userListStringRoot,new TypeReference<List<User>>(){});//使用UserList类UserList userListClass = new UserList();userListClass.setUserList(userList);String userListClassString = JacksonUtil.toJson(userListClass);UserList userListClassJason = JacksonUtil.jsonToBean(userListClassString, UserList.class);String userListClassStringRoot = JacksonUtil.toJsonWithRoot(userListClass);UserList userListClassJasonRoot = JacksonUtil.jsonToBeanWithRoot(userListClassStringRoot, UserList.class);String userMapString = JacksonUtil.toJson(userMap);Map<String, User> userMapJson = JacksonUtil.jsonToBeanByTypeReference(userMapString,new TypeReference<Map<String, User>>(){});String userMapStringRoot = JacksonUtil.toJsonWithRoot(userMap);//这种使用方法，得到的userMapJsonRoot是nullMap<String, User> userMapJsonRoot = JacksonUtil.jsonToBeanByTypeReferenceWithRoot(userMapStringRoot,new TypeReference<Map<String, User>>(){});//使用UserMap类UserMap userMapClass = new UserMap();userMapClass.setUserMap(userMap);String userMapClassString = JacksonUtil.toJson(userMapClass);UserMap userMapClassJson = JacksonUtil.jsonToBean(userMapClassString, UserMap.class);String userMapClassStringRoot = JacksonUtil.toJsonWithRoot(userMapClass);UserMap userMapClassJsonRoot = JacksonUtil.jsonToBeanWithRoot(userMapClassStringRoot, UserMap.class);}
}

代码分析及运行结果

1 关于Google guava
google guava所包含的内容远不止在Demo中使用的样子。由于本篇博文的重点在json，这里对guava不详细说明，给出链接资料：http://ifeve.com/google-guava/
在java 7之前，在构造新的泛型集合时要反复重新声明泛型。如下所示：

List<User> userList = new ArrayList<User>();

这样写太繁琐，因此guava推出了能够推断泛型的静态工厂方法：

List<User> userList = Lists.newArrayList();

2 json与java对象之间的转换
java对象转换成json，使用JacksonUtil.toJson ，这个方法调用过程中会调用java bean的get方法。如果java bean中不存在get方法也不影响转换的过程。
json转换成java对象，使用JacksonUtil.jsonToBean , 这个方法调用过程中首先会调用java bean的默认构造函数。如果java bean没有其他构造函数的话，编译器会自动添加默认构造函数。总之，默认构造函数必须要有，否则会报错。由json转java bean时也会调用setter方法。如果java bean中不存在set方法也不影响转换的过程。

        //会调用get方法String userString = JacksonUtil.toJson(user);//会调用无参构造函数,set方法User userJson = JacksonUtil.jsonToBean(userString, User.class);Map<String,String> userJsonMap = JacksonUtil.jsonToBean(userString, Map.class);

为了检验默认构造方法，setter，getter方法的调用，在POJO中有打印信息。
上面代码的执行结果，如下所示。

userString的内容：

{"AGE":-26,"BIRTHDAY":{"day":8,"month":8,"year":2000},"MALE":true,"NAME":"宝宝","PHONE":["15888888888","15222222222"]}

从上面可以看到，键值对的排序都是按照字母顺序排序的，而且还是大写的。原因如下：

            mapper = new ObjectMapper();//对象属性按字母顺序排列mapper.configure(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY, true);

在创建POJO User.java时使用了注解。

    @JsonProperty("NAME")private String name;@JsonProperty("AGE")private int age;@JsonProperty("PHONE")private String[] phone;@JsonProperty("BIRTHDAY")private Birthday birthday;@JsonProperty("MALE")private boolean male;

userJson对象的内容

userJsonMap的内容

3 从json字符串中直接得到某一属性的值

        JsonNode name = JacksonUtil.getValueFromJson(userString, "NAME");JsonNode age = JacksonUtil.getValueFromJson(userString, "AGE");JsonNode phoneNode = JacksonUtil.getValueFromJson(userString, "PHONE");JsonNode birthdayNode = JacksonUtil.getValueFromJson(userString, "BIRTHDAY");JsonNode maleNode = JacksonUtil.getValueFromJson(userString, "MALE");String nameStr = name.toString();int ageInt = age.intValue();//List<String> phoneArr = phoneNode.findValuesAsText("PHONE");String[] phoneArr = new String[phoneNode.size()];for (int i = 0; i < phoneNode.size(); i++) {phoneArr[i] = phoneNode.get(i).toString();}Birthday birthdayObj = new Birthday();//会分别调用Birthday的3个setter方法birthdayObj.setYear(birthdayNode.get("year").intValue());birthdayObj.setMonth(birthdayNode.get("month").intValue());birthdayObj.setDay(birthdayNode.get("day").intValue());boolean male = maleNode.booleanValue();

4 在json字符串中显示根的名字

        String userString2 = JacksonUtil.toJsonWithRoot(user);//使用这种内部数据将会是nullUser userJson2_1 = JacksonUtil.jsonToBean(userString2, User.class);User userJson2_2 = JacksonUtil.jsonToBeanWithRoot(userString2, User.class);

userString2的内容如下所示：

{"FAN":{"AGE":-26,"BIRTHDAY":{"day":8,"month":8,"year":2000},"MALE":true,"NAME":"宝宝","PHONE":["15888888888","15222222222"]}}

之所以会显示头时因为，有注解：

@JsonRootName(value = "FAN")
@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY)
public class User {
}

userJson2_1和userJson2_2的内容如下：

userJson2_1是null的，因为json串是有root的，重新解析时也要使用有root的。

5 关于集合List

        String userListString = JacksonUtil.toJson(userList);List<User> userListJson = JacksonUtil.jsonToBeanByTypeReference(userListString,new TypeReference<List<User>>(){});String userListStringRoot = JacksonUtil.toJsonWithRoot(userList);//这种使用方法，得到的userListJsonRoot是nullList<User> userListJsonRoot = JacksonUtil.jsonToBeanByTypeReferenceWithRoot(userListStringRoot,new TypeReference<List<User>>(){});

userListString的内容如下：

[{"AGE":-26,"BIRTHDAY":{"day":8,"month":8,"year":2000},"MALE":true,"NAME":"宝宝","PHONE":["15888888888","15222222222"]},{"AGE":25,"BIRTHDAY":{"day":8,"month":8,"year":2000},"MALE":false,"NAME":"fan","PHONE":["15888888888","15222222222"]}]

userListJson的内容：

但是有了root之后就有问题了：

因此对于集合最好不要使用jsonToBeanByTypeReference这种方式来将json转换成java bean。当遇到集合时，最好能新建一个集合的类。

//使用UserList类UserList userListClass = new UserList();userListClass.setUserList(userList);String userListClassString = JacksonUtil.toJson(userListClass);UserList userListClassJason = JacksonUtil.jsonToBean(userListClassString, UserList.class);String userListClassStringRoot = JacksonUtil.toJsonWithRoot(userListClass);UserList userListClassJasonRoot = JacksonUtil.jsonToBeanWithRoot(userListClassStringRoot, UserList.class);

userListClassString的内容如下：

{"USERLIST":[{"AGE":-26,"BIRTHDAY":{"day":8,"month":8,"year":2000},"MALE":true,"NAME":"宝宝","PHONE":["15888888888","15222222222"]},{"AGE":25,"BIRTHDAY":{"day":8,"month":8,"year":2000},"MALE":false,"NAME":"fan","PHONE":["15888888888","15222222222"]}]}

userListClassStringRoot的内容如下：

{"AAAAA":{"USERLIST":[{"AGE":-26,"BIRTHDAY":{"day":8,"month":8,"year":2000},"MALE":true,"NAME":"宝宝","PHONE":["15888888888","15222222222"]},{"AGE":25,"BIRTHDAY":{"day":8,"month":8,"year":2000},"MALE":false,"NAME":"fan","PHONE":["15888888888","15222222222"]}]}}

6 （1）map的情况跟list类似

        String userMapString = JacksonUtil.toJson(userMap);Map<String, User> userMapJson = JacksonUtil.jsonToBeanByTypeReference(userMapString,new TypeReference<Map<String, User>>(){});String userMapStringRoot = JacksonUtil.toJsonWithRoot(userMap);//这种使用方法，得到的userMapJsonRoot是nullMap<String, User> userMapJsonRoot = JacksonUtil.jsonToBeanByTypeReferenceWithRoot(userMapStringRoot,new TypeReference<Map<String, User>>(){});

userMapString的内容：

{"user2":{"AGE":25,"BIRTHDAY":{"day":8,"month":8,"year":2000},"MALE":false,"NAME":"fan","PHONE":["15888888888","15222222222"]},"user1":{"AGE":-26,"BIRTHDAY":{"day":8,"month":8,"year":2000},"MALE":true,"NAME":"宝宝","PHONE":["15888888888","15222222222"]}}

userMapStringRoot的内容：

{"HashMap":{"user2":{"AGE":25,"BIRTHDAY":{"day":8,"month":8,"year":2000},"MALE":false,"NAME":"fan","PHONE":["15888888888","15222222222"]},"user1":{"AGE":-26,"BIRTHDAY":{"day":8,"month":8,"year":2000},"MALE":true,"NAME":"宝宝","PHONE":["15888888888","15222222222"]}}}

（2）

//使用UserMap类UserMap userMapClass = new UserMap();userMapClass.setUserMap(userMap);String userMapClassString = JacksonUtil.toJson(userMapClass);UserMap userMapClassJson = JacksonUtil.jsonToBean(userMapClassString, UserMap.class);String userMapClassStringRoot = JacksonUtil.toJsonWithRoot(userMapClass);UserMap userMapClassJsonRoot = JacksonUtil.jsonToBeanWithRoot(userMapClassStringRoot, UserMap.class);

userMapClassString的内容：

{"USERMAP":{"user2":{"AGE":25,"BIRTHDAY":{"day":8,"month":8,"year":2000},"MALE":false,"NAME":"fan","PHONE":["15888888888","15222222222"]},"user1":{"AGE":-26,"BIRTHDAY":{"day":8,"month":8,"year":2000},"MALE":true,"NAME":"宝宝","PHONE":["15888888888","15222222222"]}}}

userMapClassStringRoot的内容：

{"BB":{"USERMAP":{"user2":{"AGE":25,"BIRTHDAY":{"day":8,"month":8,"year":2000},"MALE":false,"NAME":"fan","PHONE":["15888888888","15222222222"]},"user1":{"AGE":-26,"BIRTHDAY":{"day":8,"month":8,"year":2000},"MALE":true,"NAME":"宝宝","PHONE":["15888888888","15222222222"]}}}}