fastjson SerializerFeature序列化属性
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Map < String , Object > jsonMap = new HashMap< String , Object>(); jsonMap.put("a",1); jsonMap.put("b",""); jsonMap.put("c",null); jsonMap.put("d","wuzhuti.cn"); String str = JSONObject.toJSONString(jsonMap); System.out.println(str); //输出结果:{"a":1,"b":"",d:"wuzhuti.cn"}
从输出结果可以看出,null对应的key已经被过滤掉;这明显不是我们想要的结果,这时我们就需要用到fastjson的SerializerFeature序列化属性
也就是这个方法:JSONObject.toJSONString(Object object, SerializerFeature… features)
SerializerFeature有用的一些枚举值
QuoteFieldNames———-输出key时是否使用双引号,默认为true WriteMapNullValue——–是否输出值为null的字段,默认为false WriteNullNumberAsZero—-数值字段如果为null,输出为0,而非null WriteNullListAsEmpty—–List字段如果为null,输出为[],而非null WriteNullStringAsEmpty—字符类型字段如果为null,输出为”“,而非null WriteNullBooleanAsFalse–Boolean字段如果为null,输出为false,而非null
例如:
Map < String , Object > jsonMap = new HashMap< String , Object>(); jsonMap.put("a",1); jsonMap.put("b",""); jsonMap.put("c",null); jsonMap.put("d","wuzhuti.cn"); String str = JSONObject.toJSONString(jsonMap,SerializerFeature.WriteMapNullValue); System.out.println(str); //输出结果:{"a":1,"b":"","c":null,"d":"wuzhuti.cn"}
但是,如果把WriteNullStringAsEmpty也加进去,为毛不起作用?
String str = JSONObject.toJSONString(jsonMap,SerializerFeature.WriteMapNullValue,SerializerFeature.WriteNullStringAsEmpty); System.out.println(str); //输出结果:{"a":1,"b":"","c":null,"d":"wuzhuti.cn"}
目前的解决办法是加一个过滤器
private ValueFilter filter = new ValueFilter() { @Override public Object process(Object obj, String s, Object v) { if(v==null) return ""; return v; }};JSON.toJSONString(jsonMap, filter)
fastjson github: https://github.com/alibaba/fastjson
SerializerFeature.WriteMapNullValue 是否输出值为null的字段,默认为false也就是说有null时会输出而不是忽略(默认策略是忽略,所以看不到为null的字段)
WriteNullStringAsEmpty—字符类型字段如果为null,输出为”“,而非null
注意是字段是字段是字段,而不是json.put(“key”,null),所以用它时,字段为null的可以转换为空字符串。
如果让输出的json中所有为null的字符串都变成空字符串,最简单的做法就是加一个值过滤器,这样就避免了有的字段为null,有的字段为空字符的现象。
public class Demo1 { public class Student { private String name; private int age; private boolean isMale; private Student gf; public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public boolean isMale() { return isMale; } public void setMale(boolean isMale) { this.isMale = isMale; } public Student getGf() { return gf; } public void setGf(Student gf) { this.gf = gf; } } private static ValueFilter filter = new ValueFilter() { @Override public Object process(Object obj, String s, Object v) { if (v == null) return ""; return v; } }; public static void main(String[] args) { new Demo1().foo(); new Demo1().bar(); } private void foo() { System.out.println("foo()---------------------------"); JSONObject j1 = new JSONObject(); j1.put("name", "zhangsan"); j1.put("age", 13); j1.put("isMale", true); j1.put("gf", null); Map<String, Object> fav = new HashMap<String, Object>(); Set<String> books = new HashSet<String>(); books.add("三国"); books.add("史记"); fav.put("history", books); String[] arts = new String[] {}; fav.put("arts", arts); String[] musics = new String[] { "北京欢迎你", "画心" }; fav.put("musics", musics); List<String> sports = new ArrayList<String>(); fav.put("sports", sports); j1.put("fav", fav); List<Student> classmates = new ArrayList<Student>(); classmates.add(new Student()); Student lisi = new Student(); lisi.setMale(false); lisi.setAge(11); classmates.add(lisi); Student zhangsan = new Student(); zhangsan.setAge(13); zhangsan.setName("张三"); zhangsan.setMale(true); zhangsan.setGf(lisi); classmates.add(zhangsan); j1.put("classmates", classmates); String str = null; j1.put("str", str); System.out.println(j1.toString()); System.out .println(JSON.toJSONString(j1, SerializerFeature.WriteMapNullValue, SerializerFeature.WriteNullStringAsEmpty)); System.out.println( JSON.toJSONString(j1, filter, SerializerFeature.WriteMapNullValue, SerializerFeature.WriteNullStringAsEmpty)); System.out.println(JSON.toJSONString(j1, SerializerFeature.WriteNullStringAsEmpty)); System.out.println(JSON.toJSONString(j1, filter, SerializerFeature.WriteNullStringAsEmpty)); Map<String, JSONObject> m = new HashMap<String, JSONObject>(); m.put("key", j1); System.out.println( JSON.toJSONString(m, SerializerFeature.WriteNonStringKeyAsString, SerializerFeature.WriteNullStringAsEmpty)); System.out.println(JSON.toJSONString(m, filter, SerializerFeature.WriteNonStringKeyAsString, SerializerFeature.WriteNullStringAsEmpty)); } private void bar() { System.out.println("bar()---------------------------"); Student zhangsan = new Student(); zhangsan.setAge(13); zhangsan.setName("张三"); zhangsan.setMale(true); Student lisi = new Student(); // lisi.setName("lisi"); lisi.setMale(false); lisi.setAge(11); zhangsan.setGf(lisi); System.out.println( JSON.toJSONString(zhangsan, SerializerFeature.WriteMapNullValue, SerializerFeature.WriteNullStringAsEmpty)); System.out.println(JSON.toJSONString(zhangsan, SerializerFeature.WriteMapNullValue)); System.out.println(JSON.toJSONString(zhangsan, SerializerFeature.WriteNullStringAsEmpty)); System.out.println(JSON.toJSONString(zhangsan)); System.out.println(JSON.toJSONString(zhangsan, filter)); System.out.println(JSON.toJSONString(zhangsan, filter, SerializerFeature.WriteMapNullValue, SerializerFeature.WriteNullStringAsEmpty)); }}
foo()---------------------------{"isMale":true,"name":"zhangsan","classmates":[{"age":0,"male":false},{"age":11,"male":false},{"age":13,"gf":{"$ref":"$.classmates[1]"},"male":true,"name":"张三"}],"fav":{"sports":[],"musics":["北京欢迎你","画心"],"history":["史记","三国"],"arts":[]},"age":13}{"str":null,"isMale":true,"name":"zhangsan","classmates":[{"age":0,"gf":null,"male":false,"name":""},{"age":11,"gf":null,"male":false,"name":""},{"age":13,"gf":{"$ref":"$.classmates[1]"},"male":true,"name":"张三"}],"fav":{"sports":[],"musics":["北京欢迎你","画心"],"history":["史记","三国"],"arts":[]},"age":13,"gf":null}{"str":"","isMale":true,"name":"zhangsan","classmates":[{"age":0,"gf":"","male":false,"name":""},{"age":11,"gf":"","male":false,"name":""},{"age":13,"gf":{"$ref":"$.classmates[1]"},"male":true,"name":"张三"}],"fav":{"sports":[],"musics":["北京欢迎你","画心"],"history":["史记","三国"],"arts":[]},"age":13,"gf":""}{"isMale":true,"name":"zhangsan","classmates":[{"age":0,"male":false},{"age":11,"male":false},{"age":13,"gf":{"$ref":"$.classmates[1]"},"male":true,"name":"张三"}],"fav":{"sports":[],"musics":["北京欢迎你","画心"],"history":["史记","三国"],"arts":[]},"age":13}{"str":"","isMale":true,"name":"zhangsan","classmates":[{"age":0,"gf":"","male":false,"name":""},{"age":11,"gf":"","male":false,"name":""},{"age":13,"gf":{"$ref":"$.classmates[1]"},"male":true,"name":"张三"}],"fav":{"sports":[],"musics":["北京欢迎你","画心"],"history":["史记","三国"],"arts":[]},"age":13,"gf":""}{"key":{"isMale":true,"name":"zhangsan","classmates":[{"age":0,"male":false},{"age":11,"male":false},{"age":13,"gf":{"$ref":"$.key.classmates[1]"},"male":true,"name":"张三"}],"fav":{"sports":[],"musics":["北京欢迎你","画心"],"history":["史记","三国"],"arts":[]},"age":13}}{"key":{"str":"","isMale":true,"name":"zhangsan","classmates":[{"age":0,"gf":"","male":false,"name":""},{"age":11,"gf":"","male":false,"name":""},{"age":13,"gf":{"$ref":"$.key.classmates[1]"},"male":true,"name":"张三"}],"fav":{"sports":[],"musics":["北京欢迎你","画心"],"history":["史记","三国"],"arts":[]},"age":13,"gf":""}}bar()---------------------------{"age":13,"gf":{"age":11,"gf":null,"male":false,"name":""},"male":true,"name":"张三"}{"age":13,"gf":{"age":11,"gf":null,"male":false,"name":null},"male":true,"name":"张三"}{"age":13,"gf":{"age":11,"male":false},"male":true,"name":"张三"}{"age":13,"gf":{"age":11,"male":false},"male":true,"name":"张三"}{"age":13,"gf":{"age":11,"gf":"","male":false,"name":""},"male":true,"name":"张三"}{"age":13,"gf":{"age":11,"gf":"","male":false,"name":""},"male":true,"name":"张三"}
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