Jackson第一篇【JSON字符串、实体之间的相互转换】

既然你看到这篇文章相信你已经了解JSON的好处了，那么废话不多说直接进入主题。

Jackson是java中众多json处理工具的一个，比起常见的Json-lib,Gson要快一些。

Jackson的官网：http://jackson.codehaus.org/

里面可以下载Jackson的Jar包 注意jackson依赖：Apache的commons-loggin。

下面聊一下Jackson的常见用法==================================

Bean----->JSON

Java代码



public static String beanToJson(Object obj) throws IOException {

// 这里异常都未进行处理，而且流的关闭也不规范。开发中请勿这样写，如果发生异常流关闭不了

ObjectMapper mapper = CommonUtil.getMapperInstance(false);

StringWriter writer = new StringWriter();

JsonGenerator gen = new JsonFactory().createJsonGenerator(writer);

mapper.writeValue(gen, obj);

gen.close();

String json = writer.toString();

writer.close();

return json;

}

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public static String beanToJson(Object obj) throws IOException {

// 这里异常都未进行处理，而且流的关闭也不规范。开发中请勿这样写，如果发生异常流关闭不了

ObjectMapper mapper = CommonUtil.getMapperInstance(false);

StringWriter writer = new StringWriter();

JsonGenerator gen = new JsonFactory().createJsonGenerator(writer);

mapper.writeValue(gen, obj);

gen.close();

String json = writer.toString();

writer.close();

return json;

}

JSON------>Bean

Java代码



public static Object jsonToBean(String json, Class<?> cls) throws Exception {

Object vo = mapper.readValue(json, cls);

return vo;

}

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public static Object jsonToBean(String json, Class<?> cls) throws Exception {

Object vo = mapper.readValue(json, cls);

return vo;

}

好了方法写完了咱们测试一下吧 看看他是否支持复杂类型的转换

Java代码



public static void main(String[] args) throws Exception {

// 准备数据

List<Person> pers = new ArrayList<Person>();

Person p = new Person("张三", 46);

pers.add(p);

p = new Person("李四", 19);

pers.add(p);

p = new Person("王二麻子", 23);

pers.add(p);

TestVo vo = new TestVo("一个容器而已", pers);

// 实体转JSON字符串

String json = beanToJson(vo);

System.out.println("Bean>>>Json----" + json);

// 字符串转实体

TestVo vo2 = (TestVo)jsonToBean(json, TestVo.class);

System.out.println("Json>>Bean--与开始的对象是否相等：" + vo2.equals(vo));

}

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public static void main(String[] args) throws Exception {

// 准备数据

List<Person> pers = new ArrayList<Person>();

Person p = new Person("张三", 46);

pers.add(p);

p = new Person("李四", 19);

pers.add(p);

p = new Person("王二麻子", 23);

pers.add(p);

TestVo vo = new TestVo("一个容器而已", pers);

// 实体转JSON字符串

String json = beanToJson(vo);

System.out.println("Bean>>>Json----" + json);

// 字符串转实体

TestVo vo2 = (TestVo)jsonToBean(json, TestVo.class);

System.out.println("Json>>Bean--与开始的对象是否相等：" + vo2.equals(vo));

}

输出结果

Bean>>>Json----{"voName":"一个容器而已","pers":[{"name":"张三","age":46},{"name":"李四","age":19},{"name":"王二麻子","age":23}]}

Json>>Bean--与开始的对象是否相等：true

从结果可以看出从咱们转换的方法是对的，本文只是对Jackson的一个最简单的使用介绍。接下来的几篇文章咱们深入研究一下这玩意到底有多强大！

下面是本人涉及到的Bean 以及 CommonUtil

Java代码



public class CommonUtil {

private static ObjectMapper mapper;

/**

* 一个破ObjectMapper而已，你为什么不直接new 还搞的那么复杂。接下来的几篇文章我将和你一起研究这个令人蛋疼的问题

*

* @param createNew

* 是否创建一个新的Mapper

* @return

*/

public static synchronized ObjectMapper getMapperInstance(boolean createNew) {

if (createNew) {

return new ObjectMapper();

} else if (mapper == null) {

mapper = new ObjectMapper();

}

return mapper;

}

}

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public class CommonUtil {

private static ObjectMapper mapper;

/**

* 一个破ObjectMapper而已，你为什么不直接new 还搞的那么复杂。接下来的几篇文章我将和你一起研究这个令人蛋疼的问题

*

* @param createNew

* 是否创建一个新的Mapper

* @return

*/

public static synchronized ObjectMapper getMapperInstance(boolean createNew) {

if (createNew) {

return new ObjectMapper();

} else if (mapper == null) {

mapper = new ObjectMapper();

}

return mapper;

}

}

Java代码



public class Person {

private String name;

private int age;

public Person() {

}

public Person(String name, int age) {

super();

this.name = name;

this.age = age;

}

public int getAge() {

return age;

}

public void setAge(int age) {

this.age = age;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

@Override

public boolean equals(Object obj) {

if (this == obj) {

return true;

}

if (obj == null) {

return false;

}

if (getClass() != obj.getClass()) {

return false;

}

Person other = (Person) obj;

if (age != other.age) {

return false;

}

if (name == null) {

if (other.name != null) {

return false;

}

} else if (!name.equals(other.name)) {

return false;

}

return true;

}

}

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public class Person {

private String name;

private int age;

public Person() {

}

public Person(String name, int age) {

super();

this.name = name;

this.age = age;

}

public int getAge() {

return age;

}

public void setAge(int age) {

this.age = age;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

@Override

public boolean equals(Object obj) {

if (this == obj) {

return true;

}

if (obj == null) {

return false;

}

if (getClass() != obj.getClass()) {

return false;

}

Person other = (Person) obj;

if (age != other.age) {

return false;

}

if (name == null) {

if (other.name != null) {

return false;

}

} else if (!name.equals(other.name)) {

return false;

}

return true;

}

}

Java代码



public class TestVo {

private String voName;

private List<Person> pers;

public TestVo() {

}

public TestVo(String voName, List<Person> pers) {

super();

this.voName = voName;

this.pers = pers;

}

public String getVoName() {

return voName;

}

public void setVoName(String voName) {

this.voName = voName;

}

public List<Person> getPers() {

return pers;

}

public void setPers(List<Person> pers) {

this.pers = pers;

}

@Override

public boolean equals(Object obj) {

if (this == obj) {

return true;

}

if (obj == null) {

return false;

}

if (getClass() != obj.getClass()) {

return false;

}

TestVo other = (TestVo) obj;

if (pers == null) {

if (other.pers != null) {

return false;

}

} else if (pers.size() != other.pers.size()) {

return false;

} else {

for (int i = 0; i < pers.size(); i++) {

if (!pers.get(i).equals(other.pers.get(i))) {

return false;

}

}

}

if (voName == null) {

if (other.voName != null) {

return false;

}

} else if (!voName.equals(other.voName)) {

return false;

}

return true;

}

}