JAVA实现json和对象间的相互转换

一、新建一个项目，导入这两个jar包，下载见附件：

jackson-core-asl-1.9.12.jar

jackson-mapper-asl-1.9.12.jar

二、新建一个工具类

JsonMapper.java

Java代码

package com.ebiz.logic.service.impl;

import java.io.IOException;

import java.text.SimpleDateFormat;

import java.util.List;

import org.apache.commons.lang3.StringUtils;

import org.codehaus.jackson.JsonNode;

import org.codehaus.jackson.JsonProcessingException;

import org.codehaus.jackson.map.DeserializationConfig;

import org.codehaus.jackson.map.ObjectMapper;

import org.codehaus.jackson.map.SerializationConfig;

import org.codehaus.jackson.map.annotate.JsonSerialize.Inclusion;

import org.codehaus.jackson.map.util.JSONPObject;

import org.codehaus.jackson.type.JavaType;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

import com.ebiz.framework.util.date.DateUtil;

/**

* 简单封装Jackson，实现JSON String<->Java Object的Mapper.

*

* 封装不同的输出风格, 使用不同的builder函数创建实例.

*

*/

public class JsonMapper {

private static Logger logger = LoggerFactory.getLogger(JsonMapper.class);

private ObjectMapper mapper;

public JsonMapper(Inclusion inclusion) {

mapper = new ObjectMapper();

//设置输出时包含属性的风格

mapper.setSerializationInclusion(inclusion);

//设置输入时忽略在JSON字符串中存在但Java对象实际没有的属性

mapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);

//禁止使用int代表Enum的order()來反序列化Enum,非常危險

mapper.configure(DeserializationConfig.Feature.FAIL_ON_NUMBERS_FOR_ENUMS, true);

}

/**

* 创建输出全部属性到Json字符串的Mapper.

*/

public static JsonMapper buildNormalMapper() {

return new JsonMapper(Inclusion.ALWAYS);

}

/**

* 创建只输出非空属性到Json字符串的Mapper.

*/

public static JsonMapper buildNonNullMapper() {

return new JsonMapper(Inclusion.NON_NULL);

}

/**

* 创建只输出初始值被改变的属性到Json字符串的Mapper.

*/

public static JsonMapper buildNonDefaultMapper() {

return new JsonMapper(Inclusion.NON_DEFAULT);

}

/**

* 创建只输出非Null且非Empty(如List.isEmpty)的属性到Json字符串的Mapper.

*/

public static JsonMapper buildNonEmptyMapper() {

return new JsonMapper(Inclusion.NON_EMPTY);

}

/**

* 如果对象为Null, 返回"null".

* 如果集合为空集合, 返回"[]".

*/

public String toJson(Object object) {

try {

return mapper.writeValueAsString(object);

} catch (IOException e) {

throw NestedException.wrap(e);

}

}

/**

* 如果JSON字符串为Null或"null"字符串, 返回Null.

* 如果JSON字符串为"[]", 返回空集合.

*

* 如需读取集合如List/Map, 且不是List<String>这种简单类型时,先使用函數constructParametricType构造类型.

* @see #constructParametricType(Class, Class...)

*/

public <T> T fromJson(String jsonString, Class<T> clazz) {

if (StringUtils.isEmpty(jsonString)) {

return null;

}

try {

return mapper.readValue(jsonString, clazz);

} catch (IOException e) {

throw NestedException.wrap(e);

}

}

/**

* 如果JSON字符串为Null或"null"字符串, 返回Null.

* 如果JSON字符串为"[]", 返回空集合.

*

* 如需读取集合如List/Map, 且不是List<String>这种简单类型时,先使用函數constructParametricType构造类型.

* @see #constructParametricType(Class, Class...)

*/

@SuppressWarnings("unchecked")

public <T> T fromJson(String jsonString, JavaType javaType) {

if (StringUtils.isEmpty(jsonString)) {

return null;

}

try {

return (T) mapper.readValue(jsonString, javaType);

} catch (IOException e) {

throw NestedException.wrap(e);

}

}

@SuppressWarnings("unchecked")

public <T> T fromJson(String jsonString, Class<?> parametrized, Class<?>... parameterClasses) {

return (T) this.fromJson(jsonString, constructParametricType(parametrized, parameterClasses));

}

@SuppressWarnings("unchecked")

public <T> List<T> fromJsonToList(String jsonString, Class<T> classMeta){

return (List<T>) this.fromJson(jsonString,constructParametricType(List.class, classMeta));

}

@SuppressWarnings("unchecked")

public <T> T fromJson(JsonNode node, Class<?> parametrized, Class<?>... parameterClasses) {

JavaType javaType = constructParametricType(parametrized, parameterClasses);

try {

return (T) mapper.readValue(node, javaType);

} catch (IOException e) {

throw NestedException.wrap(e);

}

}

@SuppressWarnings("unchecked")

public <T> T pathAtRoot(String json, String path, Class<?> parametrized, Class<?>... parameterClasses){

JsonNode rootNode = parseNode(json);

JsonNode node = rootNode.path(path);

return (T) fromJson(node, parametrized, parameterClasses);

}

@SuppressWarnings("unchecked")

public <T> T pathAtRoot(String json, String path, Class<T> clazz){

JsonNode rootNode = parseNode(json);

JsonNode node = rootNode.path(path);

return (T) fromJson(node, clazz);

}

/**

* 構造泛型的Type如List<MyBean>, 则调用constructParametricType(ArrayList.class,MyBean.class)

* Map<String,MyBean>则调用(HashMap.class,String.class, MyBean.class)

*/

public JavaType constructParametricType(Class<?> parametrized, Class<?>... parameterClasses) {

return mapper.getTypeFactory().constructParametricType(parametrized, parameterClasses);

}

/**

* 當JSON裡只含有Bean的部分屬性時，更新一個已存在Bean，只覆蓋該部分的屬性.

*/

@SuppressWarnings("unchecked")

public <T> T update(T object, String jsonString) {

try {

return (T) mapper.readerForUpdating(object).readValue(jsonString);

} catch (JsonProcessingException e) {

logger.warn("update json string:" + jsonString + " to object:" + object + " error.", e);

} catch (IOException e) {

logger.warn("update json string:" + jsonString + " to object:" + object + " error.", e);

}

return null;

}

/**

* 輸出JSONP格式數據.

*/

public String toJsonP(String functionName, Object object) {

return toJson(new JSONPObject(functionName, object));

}

/**

* 設定是否使用Enum的toString函數來讀寫Enum,

* 為False時時使用Enum的name()函數來讀寫Enum, 默認為False.

* 注意本函數一定要在Mapper創建後, 所有的讀寫動作之前調用.

*/

public void setEnumUseToString(boolean value) {

mapper.configure(SerializationConfig.Feature.WRITE_ENUMS_USING_TO_STRING, value);

mapper.configure(DeserializationConfig.Feature.READ_ENUMS_USING_TO_STRING, value);

}

/**

* 取出Mapper做进一步的设置或使用其他序列化API.

*/

public ObjectMapper getMapper() {

return mapper;

}

public JsonNode parseNode(String json){

try {

return mapper.readValue(json, JsonNode.class);

} catch (IOException e) {

throw NestedException.wrap(e);

}

}

/**

* 输出全部属性

* @param object

* @return

*/

public static String toNormalJson(Object object){

return new JsonMapper(Inclusion.ALWAYS).toJson(object);

}

/**

* 输出非空属性

* @param object

* @return

*/

public static String toNonNullJson(Object object){

return new JsonMapper(Inclusion.NON_NULL).toJson(object);

}

/**

* 输出初始值被改变部分的属性

* @param object

* @return

*/

public static String toNonDefaultJson(Object object){

return new JsonMapper(Inclusion.NON_DEFAULT).toJson(object);

}

/**

* 输出非Null且非Empty(如List.isEmpty)的属性

* @param object

* @return

*/

public static String toNonEmptyJson(Object object){

return new JsonMapper(Inclusion.NON_EMPTY).toJson(object);

}

public void setDateFormat(String dateFormat){

mapper.setDateFormat(new SimpleDateFormat(dateFormat));

}

public static String toLogJson(Object object){

JsonMapper jsonMapper = new JsonMapper(Inclusion.NON_EMPTY);

jsonMapper.setDateFormat(DateUtil.yyyy_MM_dd_HH_mm_ss);

return jsonMapper.toJson(object);

}

}

三、再提供一个异常类

NestedException.java

Java代码

package com.ebiz.logic.service.impl;

public class NestedException extends RuntimeException {

private static final long serialVersionUID = 5893258079497055346L;

private Throwable throwable;

private NestedException(Throwable t) {

this.throwable = t;

}

/** Wraps another exeception in a RuntimeException. */

public static RuntimeException wrap(Throwable t) {

if (t instanceof RuntimeException)

return (RuntimeException) t;

return new NestedException(t);

}

public Throwable getCause() {

return this.throwable;

}

public void printStackTrace() {

this.throwable.printStackTrace();

}

}

新建两个实体

Student.java

Java代码

package com.ebiz.uniservice.fightdata.test;

import java.util.List;

public class Student {

private String name;

private int age;

private List<Teacher> teachers;

public void setName(String name) {

this.name = name;

}

public String getName() {

return name;

}

public void setAge(int age) {

this.age = age;

}

public int getAge() {

return age;

}

public void setTeachers(List<Teacher> teachers) {

this.teachers = teachers;

}

public List<Teacher> getTeachers() {

return teachers;

}

}

Teacher.java

Java代码

package com.ebiz.uniservice.fightdata.test;

public class Teacher {

private String name;

private int age;

public Teacher() {

}

public Teacher(String name, int age) {

super();

this.name = name;

this.age = age;

}

public void setName(String name) {

this.name = name;

}

public String getName() {

return name;

}

public void setAge(int age) {

this.age = age;

}

public int getAge() {

return age;

}

}

好了，来测试一把

JsonTest.java

Java代码

package com.ebiz.uniservice.fightdata.test;

import java.util.ArrayList;

import com.ebiz.logic.service.impl.JsonMapper;

/**

*

* @author jsqiu

*

*/

public class JsonTest {

public static void main(String[] args) {

Student student = getStudents();

Long beginTime = System.currentTimeMillis();

//bean2json

String json = JsonMapper.toLogJson(student);

System.out.println("对象转换为json：" + json);

System.out.println("转换用时：" + (System.currentTimeMillis()-beginTime) + "ms");

//json2bean，需要注意：Student类和Teacher类必须有一个空的构造方法

beginTime = System.currentTimeMillis();

//JsonMapper提供了很多创建Mapper的方法，不是非要用buildNonDefaultMapper，你可以对比几种方法的转换时间，挑个最快的

Student student2 = JsonMapper.buildNonDefaultMapper().fromJson(json, Student.class);

System.out.println("json转换成对象：" + student2);

System.out.println("转换用时：" + (System.currentTimeMillis()-beginTime) + "ms");

}

/**

* 初始化一个student

* @return

*/

private static Student getStudents() {

Teacher t1 = new Teacher("teacher1",35);

Teacher t2 = new Teacher("teacher1",25);

Teacher t3 = new Teacher("teacher1",30);

ArrayList<Teacher> teachers = new ArrayList<Teacher>();

teachers.add(t1);

teachers.add(t2);

teachers.add(t3);

Student s = new Student();

s.setAge(20);

s.setName("student1");

s.setTeachers(teachers);

return s;

}

}

输出如下：

对象转换为json：{"name":"student1","age":20,"teachers":[{"name":"teacher1","age":35},{"name":"teacher1","age":25},{"name":"teacher1","age":30}]}

转换用时：224ms

json转换成对象：com.ebiz.uniservice.fightdata.test.Student@55e55f

转换用时：25ms