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

 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  

 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

 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

 

 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;
     }
 }

 

 

 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;
     }

 }

 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;
     }
 }