标签：hang str return rgs == [1] 默认 nas his
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
上面的SerializerFeature主要是针对Object对象序列化转换时的情况（这个时候才能判断参数的类型），而在Map中，你放进入了null就是null，进行序列化时已经没法判断它原来的类型了，所以并没有起作用。要使用SerializerFeature里相关null的参数，应该传入对象进行序列化。
对规则的理解：
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。
示例代码
import java.util.ArrayList; import java.util.HashMap; import java.util.HashSet; import java.util.List; import java.util.Map; import java.util.Set; import com.alibaba.fastjson.JSON; import com.alibaba.fastjson.JSONObject; import com.alibaba.fastjson.serializer.SerializerFeature; import com.alibaba.fastjson.serializer.ValueFilter; 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"}
标签：hang str return rgs == [1] 默认 nas his
原文地址：http://www.cnblogs.com/softidea/p/6619072.html
