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;
}



[java] view plain copy print?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; }

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;
}



[java] view plain copy print?public static Object jsonToBean(String json, Class<?> cls) throws Exception {
Object vo = mapper.readValue(json, cls);
return vo;
}

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));

}



[java] view plain copy print?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));

}

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;
}
}



[java] view plain copy print?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; } }

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; } }


[java] view plain copy print?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; } }

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;
}
}