选择性将对象的属性转换为Json

上一篇写的Json转换项目中大部分情况都已经够用了，但是，有时候一个对象很多属性，而我们并不需要那么多，那么就选择性的过滤掉一些属性喽。

还有对于日期这样的属性，我们该让它以何种格式显示呢？ 这也是我们需要考虑的问题。

下面请看实例：

实体类Student.java 

public class Student {

	@Include("tt")
	private String userName;
	
	@Exclude("tt")
	private int age;
	
	@Include("tt")
	private Date birthDay;
	
	private List<String> hobbiy;
	
	/////////////////get/set方法已经省略/////////////////////////
}

我们采用注解的方式，在实体类上加上一个注解，加了注解的表示要转换成Json的，没加的则不转换，而且可以灵活的控制。

注解类：

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Include {
	String[] value() default "";
}

转换类：

public class JsonInclude {
	private static Map<String,List<String>> classfields=new HashMap<String,List<String>>();
	private JsonInclude() {
	}
/**
 * 
 * @param obj
 * @param includeTag 只将Include标签中包含此字符串的field转换成json 为null时将不过滤
 * @return
 */
	public static Object json(Object obj, String includeTag) {
		try {
			if (null != obj) {
				JsonConfig jsonConfig=null;
				if(StringUtils.isEmpty(includeTag))
					jsonConfig=getJsonConfig();
				else
					jsonConfig=getJsonConfig(includeTag);
				jsonConfig.registerJsonValueProcessor(Date.class, new JsonDateValueProcessor());  
				if (obj instanceof List ) {
					return JSONArray.fromObject(obj, jsonConfig);
				} else {
					return JSONObject.fromObject(obj, jsonConfig);
				}
			}
			return obj;
		} catch (Exception e) {
			System.out.println("json failed " + includeTag);
			System.out.println(e.getLocalizedMessage());
			System.out.println(e);
		}
		return obj;
	}

	private static JsonConfig getJsonConfig(final String includeTag) {
		JsonConfig jsonConfig = new JsonConfig();
		jsonConfig.setJsonPropertyFilter(new PropertyFilter(){
            @Override
            public boolean apply(Object obj, String name, Object value) {
            	if(value == null){
            		return true;
            	}else{
        			Class<?> objClass=obj.getClass();
        			Class<?> tempClass=obj.getClass();
        			List<String> fields=classfields.get(objClass.getName()+includeTag);
        			if(CollectionUtils.isEmpty(fields)){
        				fields=new ArrayList<String>();
        				while(objClass!=null){
            				Field[] fieldss=objClass.getDeclaredFields();
            				for(Field f:fieldss){
            					if(f.isAnnotationPresent(Include.class)){
            						String[] tag = f.getAnnotation(Include.class).value();
            						for (String str : tag) {
            							if (str.equals(includeTag)) {
            								fields.add(f.getName());
            								break;
            							}
            						}
            					}
            				}
            				objClass=objClass.getSuperclass();
            			}
        				classfields.put(tempClass.getName()+includeTag, fields);
        			}
    				for(String ff:fields){
    					if(ff.equals(name)){
    						return false;
    					}
    				}
        			return true;
            	}
            }
        });
		return jsonConfig;
	}
	private static JsonConfig getJsonConfig() {
		JsonConfig jsonConfig = new JsonConfig();
		jsonConfig.setJsonPropertyFilter(new PropertyFilter(){
            @Override
            public boolean apply(Object obj, String name, Object value) {
            	return null==value;
            }
        });
		return jsonConfig;
	}
}

这里面用到了日期格式转换的类，等最后面会贴出来。

现在就可以看测试类了：

public class IncludeTest {

	//所有属性都会转换
	public void objectNoTag(){
		Student s = new Student();
		s.setAge(45);
		s.setBirthDay(new Date());
		List<String> hobbiy = new ArrayList<String>();
		hobbiy.add("唱歌");hobbiy.add("跳舞");hobbiy.add("爬山");
		s.setHobbiy(hobbiy);
		s.setUserName("张三");
		
		System.out.println(JsonInclude.json(s, null));
	}
	
	//现在只有属性上加有@Include("tt")注解的才会转换了
	public void objectTag(){
		Student s = new Student();
		s.setAge(45);
		s.setBirthDay(new Date());
		List<String> hobbiy = new ArrayList<String>();
		hobbiy.add("唱歌");hobbiy.add("跳舞");hobbiy.add("爬山");
		s.setHobbiy(hobbiy);
		s.setUserName("张三");
		
		System.out.println(JsonInclude.json(s, "tt"));
	}
	
	public static void main(String[] args) {
		IncludeTest inc = new IncludeTest();
		inc.objectNoTag();
		inc.objectTag();
	}
	

日期转换类：

public class JsonDateValueProcessor implements JsonValueProcessor {
	
	public JsonDateValueProcessor() {
		super();
	}
	
	public JsonDateValueProcessor(String format) {
		super();
	}

	@Override
	public Object processArrayValue(Object paramObject,
			JsonConfig paramJsonConfig) {
		return process(paramObject);
	}

	@Override
	public Object processObjectValue(String paramString, Object paramObject,
			JsonConfig paramJsonConfig) {
		return process(paramObject);
	}
	
	
	private Object process(Object value){
        if(value instanceof Date){  
            return ((Date) value).getTime();
        }  
        return value == null ? "" : value.toString();  
    }

}

可能会有人觉得如果我只想去掉某一个属性，那你不会让我把剩下的属性全加你那个注解吧？ 当然不会。

我们可以再写一个嘛

注解类：

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Exclude {
	String[] value() default "";
}

转换类：

public class JsonExclude {
	
	private static Map<String,List<String>> classfields=new HashMap<String,List<String>>();
	private JsonExclude() {}
	
	/**
	 * 
	 * @param obj
	 * @param excludeTag 将过滤Exclude标签中包含此字符串的field的属 ?为null时将不过滤
	 * @return
	 */
	public static Object json(Object obj, String excludeTag) {
		try {
			if (null != obj) {
				JsonConfig jsonConfig=null;
				if(StringUtils.isEmpty(excludeTag))
					jsonConfig=getJsonConfig();
				else
					jsonConfig=getJsonConfig(excludeTag);
				jsonConfig.registerJsonValueProcessor(Date.class, new JsonDateValueProcessor());
				if (obj instanceof List) {
					return JSONArray.fromObject(obj, jsonConfig);
				} else {
					return JSONObject.fromObject(obj, jsonConfig);
				}
			}
			return obj;
		} catch (Exception e) {
			System.out.println("json failed . excludeTag={},msg={}" + excludeTag + e.getLocalizedMessage() + e);
		}
		return obj;
	}

	private static JsonConfig getJsonConfig(final String excludeTag) {
		JsonConfig jsonConfig = new JsonConfig();
		jsonConfig.setJsonPropertyFilter(new PropertyFilter(){
            @Override
            public boolean apply(Object obj, String name, Object value) {
            	if(value == null){
            		return true;
            	}else{
        			Class<?> objClass=obj.getClass();
        			Class<?> tempClass=obj.getClass();
        			List<String> fields=classfields.get(objClass.getName()+excludeTag);
        			if(CollectionUtils.isEmpty(fields)){
        				fields=new ArrayList<String>();
        				while(objClass!=null){
            				Field[] fieldss=objClass.getDeclaredFields();
            				for(Field f:fieldss){
            					if(f.isAnnotationPresent(Exclude.class)){
            						String[] tag = f.getAnnotation(Exclude.class).value();
            						for (String str : tag) {
            							if (str.equals(excludeTag)) {
            								fields.add(f.getName());
            								break;
            							}
            						}
            					}
            				}
            				objClass=objClass.getSuperclass();
            			}
        				classfields.put(tempClass.getName()+excludeTag, fields);
        			}
    				for(String ff:fields){
    					if(ff.equals(name)){
    						return true;
    					}
    				}
        			return false;
            	}
            }
        });
		return jsonConfig;
	}
	private static JsonConfig getJsonConfig() {
		JsonConfig jsonConfig = new JsonConfig();
		jsonConfig.setJsonPropertyFilter(new PropertyFilter(){
            @Override
            public boolean apply(Object obj, String name, Object value) {
            	return null==value;
            }
        });
		return jsonConfig;
	}
}

测试：

public class ExcludeTest {

	public void listTag(){
		Student s0 = new Student();
		s0.setAge(45);
		s0.setBirthDay(new Date());
		List<String> hobbiy0 = new ArrayList<String>();
		hobbiy0.add("唱歌");hobbiy0.add("跳舞");hobbiy0.add("爬山");
		s0.setHobbiy(hobbiy0);
		s0.setUserName("张三");
		
		Student s1 = new Student();
		s1.setAge(35);
		s1.setBirthDay(new Date());
		List<String> hobbiy1 = new ArrayList<String>();
		hobbiy1.add("唱歌1");hobbiy1.add("跳舞1");hobbiy1.add("爬山1");
		s1.setHobbiy(hobbiy1);
		s1.setUserName("李四");
		
		Student s2 = new Student();
		s2.setAge(25);
		s2.setBirthDay(new Date());
		List<String> hobbiy2 = new ArrayList<String>();
		hobbiy2.add("唱歌2");hobbiy2.add("跳舞2");hobbiy2.add("爬山2");
		s2.setHobbiy(hobbiy2);
		s2.setUserName("王五");
		List<Student> list = new ArrayList<Student>();
		
		list.add(s0);list.add(s1);list.add(s2);
		
		System.out.println(JsonExclude.json(list, "tt"));
	}
	
	
	public static void main(String[] args) {
		ExcludeTest exc = new ExcludeTest();
		exc.listTag();
	}