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;
    }
}