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JSONObject基本内容(三)

来源: 阅读:

参考资料:http://swiftlet.net/archives/category/json    十分感谢!!!~~

 

第三篇的内容,主要讲述的有两点: 1 .如何获取JSONObject中对应key的value。   2.如何把JSONObject转换为javaBean对象。

 

一)获取JSONObject中属性值

首先我们写一个javaBean类

public class Emp {
    private String name;
    private Integer age;
    private boolean married;
    
    public boolean isMarried() {
        return married;
    }
    public void setMarried(boolean married) {
        this.married = married;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
}

然后按正常方法,生成对象,把它转换为JSONObject,接着看注释吧~

    public static void main(String[] args) {
        Emp emp = new Emp();
        emp.setName("Rime");
        emp.setAge(23);
        emp.setMarried(false);
        
        //转换为JSONObject
        JSONObject json = JSONObject.fromObject(emp);
        System.out.println(json.toString());
        
        //利用key获取属性值,和map相似
        String name = json.getString("name");
        Integer age = json.getInt("age");
        boolean married = json.getBoolean("married");

        System.out.println(name + "," + age + "," + married);        
    }

输出结果:

{"age":23,"married":false,"name":"Rime"}
Rime,23,false

 

看到这里你或许会有疑问,(1)假如JSONObject中并没有这个key存在,会怎么样?(2)这个key对应的value的类型错了,怎么办?(3)如果value是复杂数据类型,怎么办?

既然有疑问,那么我们一个一个解决。

 

(1)我们故意把"name"写错,写成"nane",结果系统报错:

Exception in thread "main" net.sf.json.JSONException: JSONObject["nane"] not found

为了防止这种异常,我们可以用optXXX方法,来代替getXXX方法。

即:

 String name = json.optString("nane");//当jsonObject中不存在该key时,可以用optXXX来获取空值或者默认值,而不是报异常

设置默认值:

String name = json.optString("nane","notExits");

设置默认之后,当nane属性不存在时,返回notExits字符串。

 

(2)我们把程序修改一下

        String name = json.getString("age");
        boolean married = json.getBoolean("name");
        Integer age = json.getInt("name");

运行程序,会报错:

Exception in thread "main" net.sf.json.JSONException: JSONObject["name"] is not a Boolean.

Exception in thread "main" net.sf.json.JSONException: JSONObject["name"] is not a number.这一类错误。

 

特别要注意的是{"age":23,"married":false,"name":"false"},其中没带""号的false是boolean类型,带引号的是字符串类型。

还有就是大多数类型可以转换为字符串类型,但是反过来就不行了。

 

(3)复杂数据类型

写一个复杂点的bean

public class Student implements Serializable{
    private static final long serialVersionUID = 1L;
    private String sname;
    private Integer age;
    private Date birth;
    private List<String> courses;
    private Map<String,String> photo;
    private Emp emp;

然后,生成对象,给属性赋值

    public static void main(String[] args) {
        Student s = new Student();
        List<String> sList = new LinkedList<String>();
        Map<String,String> photos = new HashMap<String,String>();
        Emp emp = new Emp();
        emp.setName("me");
        emp.setAge(10);
        emp.setMarried(false);
        
        sList.add("a");
        sList.add("b");
        
        photos.put("c", "c");
        photos.put("d", "d");
        
        s.setSname("EZ");
        s.setAge(23);
        s.setBirth(new Date());
        s.setCourses(sList);
        s.setPhoto(photos);
        s.setEmp(emp);
        
        JSONObject jsonObject = JSONObject.fromObject(s);
        System.out.println(jsonObject.toString());
        
        //jsonObject转换为javaBean        
        Student student = (Student) JSONObject.toBean(jsonObject, Student.class);
        System.out.println(student.getSname() + ";" + student.getAge() + ";" +student.getBirth() + ";" + student.getCourses().get(1) + ";" + student.getPhoto().get("c") + ";" + student.getEmp());
    }

运行结果:

{"age":23,"birth":{"date":7,"day":2,"hours":17,"minutes":24,"month":6,"seconds":33,"time":1436261073641,"timezoneOffset":-480,"year":115},"courses":["a","b"],"emp":{"age":10,"married":false,"name":"me"},"photo":{"d":"d","c":"c"},"sname":"EZ"}
2015-7-7 17:24:33 net.sf.json.JSONObject toBean
信息: Property 'day' of class java.util.Date has no write method. SKIPPED.
2015-7-7 17:24:33 net.sf.json.JSONObject toBean
信息: Property 'timezoneOffset' of class java.util.Date has no write method. SKIPPED.
EZ;23;Tue Jul 07 17:24:33 CST 2015;b;c;com.vmaxtam.json.Emp@43b09468

 

虽然顺利把数据转换回去了,但是出现了警告信息,总让人无法安心下来。

如果仔细观察,可以发现,以上警告都是有关 java.util.Date 的警告,那么Date类型该如何处理呢?

并且,留意   "birth":{"date":8,"day":3,"hours":11,"minutes":11,"month":6,"seconds":31,"time":1436325091564,"timezoneOffset":-480,"year":115},

你会发现这个格式的数据十分难懂,而且我们一般只要用到yyyy-MM-dd这种格式。

 

二)Date类型

关于Date类型的转换,我们可以通过转换器来实现。

先写一个转换器:

public class JsonDateValueProcessor implements JsonValueProcessor {
    private String datePattern = "yyyy-MM-dd";

    public JsonDateValueProcessor() {
        super();
    }

    public JsonDateValueProcessor(String format) {
        super();
        this.datePattern = format;
    }

    @Override
    public Object processArrayValue(Object value, JsonConfig jsonConfig) {
        return process(value);
    }

    @Override
    public Object processObjectValue(String key, Object value,
            JsonConfig jsonConfig) {
        return process(value);
    }

    private Object process(Object value) {
        try {
            if (value instanceof Date) {
                SimpleDateFormat sdf = new SimpleDateFormat(datePattern,
                        Locale.UK);
                return sdf.format((Date) value);
            }
            return value == null ? "" : value.toString();
        } catch (Exception e) {
            return "";
        }

    }

    public String getDatePattern() {
        return datePattern;
    }

    public void setDatePattern(String pDatePattern) {
        datePattern = pDatePattern;
    }
}

然后再进行测试:

    public static void main(String[] args) {
        Student s = new Student();
        s.setBirth(new Date());
        
        JsonConfig config = new JsonConfig();
        config.registerJsonValueProcessor(Date.class, new JsonDateValueProcessor());
                
        JSONObject jsonObject = JSONObject.fromObject(s,config);
        System.out.println(jsonObject.toString());
    }

最后输出的结果

{"age":0,"birth":"2015-07-08","courses":[],"emp":null,"photo":null,"sname":""}

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