Fastjson 专题

https://github.com/eishay/jvm-serializers/wiki

TypeReference

1. 基础使用

在fastjson中提供了一个用于处理泛型反序列化的类TypeReference。

import com.alibaba.fastjson.TypeReference;

List<VO> list = JSON.parseObject("...", new TypeReference<List<VO>>() {});

如下写法有更好的性能

import com.alibaba.fastjson.TypeReference;

final static Type type = new TypeReference<List<VO>>() {}.getType();

List<VO> list = JSON.parseObject("...", type);

在这里例子中，通过TypeReference能够解决List中T的类型问题。

    @Test
    public void TestListGenerics() {
        List<UserDO> userDOList = Arrays.asList(new UserDO(1L, "Name1"), new UserDO(2L, "Name2"));
        String userListStr = JSON.toJSONString(userDOList);
        List<UserDO> userDOS = JSON.parseArray(userListStr, UserDO.class);
        assertThat(userDOS.size()).isEqualTo(userDOList.size());
        assertThat(userDOS.get(0)).isEqualToComparingFieldByField(userDOList.get(0));
        assertThat(userDOS.get(1)).isEqualToComparingFieldByField(userDOList.get(1));
        System.out.println(userDOS);
        List<UserDO> result = JSON.parseObject(userListStr, new TypeReference<List<UserDO>>() {
        }.getType());
        assertThat(result.size()).isEqualTo(userDOList.size());
        assertThat(result.get(0)).isEqualToComparingFieldByField(userDOList.get(0));
        assertThat(result.get(1)).isEqualToComparingFieldByField(userDOList.get(1));
        System.out.println(result);
    }

2. 带参数使用

在1.2.9 & 1.1.49.android版本中，TypeReference支持泛型参数，方便一些框架实现通用的反序列化类。用法如下：

2.1. 单参数例子

public class Response<T> {
     public T data;
}
public static <T> Response<T> parseToMap(String json, Class<T> type) {
     return JSON.parseObject(json,
                            new TypeReference<Response<T>>(type) {});
}

2.2. 双参数例子

public static <K, V> Map<K, V> parseToMap(String json,
                                            Class<K> keyType,
                                            Class<V> valueType) {
     return JSON.parseObject(json,
                            new TypeReference<Map<K, V>>(keyType, valueType) {
                            });
}

// 可以这样使用
String json = "{1:{name:\"ddd\"},2:{name:\"zzz\"}}";
Map<Integer, Model> map = parseToMap(json, Integer.class, Model.class);
assertEquals("ddd", map.get(1).name);
assertEquals("zzz", map.get(2).name);

https://github.com/alibaba/fastjson/wiki/TypeReference

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.TypeReference;
import com.google.gson.Gson;
import com.google.gson.JsonSyntaxException;
import com.google.gson.reflect.TypeToken;
import io.swagger.annotations.ApiModel;
import io.swagger.annotations.ApiModelProperty;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.junit.Test;

import java.lang.reflect.Type;

/**
 * @Auther: cheng.tang
 * @Date: 2019/7/31
 * @Description:
 */
public class GsonTest {

    private static final String source = "{\"code\":500,\"data\":\"\",\"msg\":\"未知异常\",\"success\":false}";

    /**
     * com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 21 path $.data
     * <p>
     * at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:226)
     * at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:131)
     * at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:222)
     * at com.google.gson.Gson.fromJson(Gson.java:922)
     * at com.google.gson.Gson.fromJson(Gson.java:887)
     * at com.google.gson.Gson.fromJson(Gson.java:836)
     * at com.zkh360.gbb.user.utils.GsonTest.gsonDeserializationTest(GsonTest.java:36)
     * at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
     * at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
     * at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
     * at java.lang.reflect.Method.invoke(Method.java:498)
     * at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
     * at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
     * at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
     * at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
     * at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
     * at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
     * at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
     * at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
     * at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
     * at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
     * at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
     * at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
     * at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
     * at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
     * at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
     * at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
     * at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
     * at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
     * Caused by: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 21 path $.data
     * at com.google.gson.stream.JsonReader.beginObject(JsonReader.java:385)
     * at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:215)
     * ... 28 more
     */
    @Test(expected = JsonSyntaxException.class)
    public void gsonDeserializationTest() {
        Gson gson = new Gson();
        Type type = new TypeToken<ResultDTO<UserIdDTO>>() {
        }.getType();
        ResultDTO<UserIdDTO> resultDTO = gson.fromJson(source, type);
        System.out.println(JSON.toJSONString(resultDTO));
    }

    @Test
    public void fastjsonDeserializationTest() {
        ResultDTO<UserIdDTO> userIdDTOResultDTO = JSON.parseObject(source, new TypeReference<ResultDTO<UserIdDTO>>() {
        });
        System.out.println(JSON.toJSONString(userIdDTOResultDTO));
    }

}

fastjson实例化对象时，如果1，true 会转换成true,其它的都为false

import com.alibaba.fastjson.JSON;
import lombok.Data;
import org.junit.Test;

import static org.assertj.core.api.Java6Assertions.assertThat;

/**
 * @author: tangcheng
 * @description:
 * @since: Created in 2018/08/03 16:31
 */
public class JSONBooleanTypeTest {

    @Test
    public void testFastJson() {
        BooleanType booleanType = new BooleanType();
        booleanType.setEnable(true);
        String output = JSON.toJSONString(booleanType);
        assertThat(output).isEqualTo("{\"enable\":true}");

        /**
         * 字符串的值除了1和true外，都是false
         */
        BooleanType serialObj = JSON.parseObject("{\"enable\":true}", BooleanType.class);
        assertThat(serialObj.getEnable()).isTrue();
        serialObj = JSON.parseObject("{\"enable\":1}", BooleanType.class);
        assertThat(serialObj.getEnable()).isTrue();

        serialObj = JSON.parseObject("{\"enable\":false}", BooleanType.class);
        assertThat(serialObj.getEnable()).isFalse();
        serialObj = JSON.parseObject("{\"enable\":2}", BooleanType.class);
        assertThat(serialObj.getEnable()).isFalse();
        serialObj = JSON.parseObject("{\"enable\":0}", BooleanType.class);
        assertThat(serialObj.getEnable()).isFalse();

        serialObj = JSON.parseObject("{\"enable\":-1}", BooleanType.class);
        assertThat(serialObj.getEnable()).isFalse();
    }

    @Data
    public static class BooleanType {
        private Boolean enable;
    }
}

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

SerializerFeature.DisableCircularReferenceDetect ，
如果没有设置这个参数会出现的问题【

FastJson如何解决循环引用/重复引用
fastjson支持循环引用/重复引用，并且是缺省打开的。
* 第一个例子序列化后输出结果为：{"1":{},"2":{"$ref":"$.1"}}
第一个对象正常序列化，第二个对象则用引用表示
* 第二个列子序列化后输出结果为：{"1":{"1":{"$ref":".."}}}

】：
如果对象中两个字段存放的是相同的List 对象，则会出现这种情况
http://www.cnblogs.com/softidea/p/5873277.html

https://blog.csdn.net/qq_35873847/article/details/78850528

代码：

                List<JobResVO> jobs = recommendJobBO.getJobs();
                resultResVO.setModern(jobs);
                resultResVO.setTraditional(jobs);

Converter中FastJson的配置：

    @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        FastJsonHttpMessageConverter httpMessageConverter = new FastJsonHttpMessageConverter();
        FastJsonConfig fastJsonConfig = new FastJsonConfig();
        fastJsonConfig.setSerializerFeatures(SerializerFeature.QuoteFieldNames,
                SerializerFeature.WriteEnumUsingToString,
                SerializerFeature.WriteMapNullValue,
                SerializerFeature.WriteDateUseDateFormat);
        fastJsonConfig.setSerializeFilters((ValueFilter) (o, s, source) -> {
            if (source == null) {
                return "";
            }
            if (source instanceof Date) {
                return ((Date) source).getTime();
            }
            return source;
        });
        httpMessageConverter.setFastJsonConfig(fastJsonConfig);
        converters.add(httpMessageConverter);
    }

解决办法：

    @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        FastJsonHttpMessageConverter httpMessageConverter = new FastJsonHttpMessageConverter();
        FastJsonConfig fastJsonConfig = new FastJsonConfig();
        fastJsonConfig.setSerializerFeatures(SerializerFeature.QuoteFieldNames,
                SerializerFeature.WriteEnumUsingToString,
                SerializerFeature.WriteMapNullValue,
                SerializerFeature.WriteDateUseDateFormat,
                SerializerFeature.DisableCircularReferenceDetect);
        fastJsonConfig.setSerializeFilters((ValueFilter) (o, s, source) -> {
            if (source == null) {
                return "";
            }
            if (source instanceof Date) {
                return ((Date) source).getTime();
            }
            return source;
        });
        httpMessageConverter.setFastJsonConfig(fastJsonConfig);
        converters.add(httpMessageConverter);
    }

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：

1. 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）

2. 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。

3. 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"}

JsonPathTestData.json

{
  "store": {
    "book": [
      {
        "category": "reference",
        "author": "Nigel Rees",
        "title": "Sayings of the Century",
        "price": 8.95
      },
      {
        "category": "fiction",
        "author": "Evelyn Waugh",
        "title": "Sword of Honour",
        "price": 12.99,
        "isbn": "0-553-21311-3"
      }
    ],
    "bicycle": {
      "color": "red",
      "price": 19.95
    }
  }
}

    @Test
    public void testJsonPath() throws IOException {
        InputStream resourceAsStream = this.getClass().getResourceAsStream("/JsonPathTestData.json");
        String jsonStr = IOUtils.toString(resourceAsStream, "utf-8");
        System.out.println(jsonStr);

        System.out.println(jsonStr);
        JSONObject jsonObject = JSON.parseObject(jsonStr);

        System.out.println("\nBook数目：" + JSONPath.eval(jsonObject, "$.store.book.size()"));
        System.out.println("第一本书title：" + JSONPath.eval(jsonObject, "$.store.book[0].title"));
        System.out.println("price大于10元的book：" + JSONPath.eval(jsonObject, "$.store.book[price > 10]"));
        System.out.println("price大于10元的title：" + JSONPath.eval(jsonObject, "$.store.book[price > 10][0].title"));
        System.out.println("category(类别)为fiction(小说)的book：" + JSONPath.eval(jsonObject, "$.store.book[category = 'fiction']"));
        System.out.println("bicycle的所有属性值" + JSONPath.eval(jsonObject, "$.store.bicycle.*"));
        System.out.println("bicycle的color和price属性值" + JSONPath.eval(jsonObject, "$.store.bicycle['color','price']"));
    }

    @Test
    public void testGenerics() {
        Result<User> result = new Result<>();
        result.setMsg("Success");
        List<User> users = new ArrayList<>();
        users.add(new User(1L, "Name1"));
        users.add(new User(2L, "Name2"));
        result.setModule(users);
        String js = JSON.toJSONString(result);
        System.out.println(js);
        //java.lang.ClassCastException: com.alibaba.fastjson.JSONObject cannot be cast to com.tangcheng.learning.json.User
//        Result<User> obj = (Result<User>) JSON.parseObject(js, Result.class);
        Result<User> userResult = JSON.parseObject(js, new TypeReference<Result<User>>() {
        });
        System.out.println(userResult);
    }

public class User {
    private Long id;
    private String name;

    public User() {
    }

    public User(Long id, String name) {
        this.id = id;
        this.name = name;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }

}

import java.util.List;

public class Result<T> {

    private String msg;

    private List<T> module;

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }

    public List<T> getModule() {
        return module;
    }

    public void setModule(List<T> module) {
        this.module = module;
    }

    @Override
    public String toString() {
        return "Result{" +
                "msg='" + msg + '\'' +
                ", module=" + module +
                '}';
    }
}

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.TypeReference;
import com.alibaba.fastjson.util.ParameterizedTypeImpl;
import lombok.Data;

@Data
public class Response<T> {
    private T data;

    @Override
    public String toString() {
        return JSON.toJSONString(this);
    }

    public static void main(String[] args) {
        String jsonText = "{\"data\":{\"id\":1,\"name\":\"张三\"}}";
        Response<User> response = JSON.parseObject(jsonText, new ParameterizedTypeImpl(new Class[]{User.class}, null, Response.class));
        /**
         * {"data":{"id":1,"name":"张三"}}
         */
        System.out.println(response);

        response = JSON.parseObject(jsonText, new TypeReference<Response<User>>() {
        });
        /**
         * {"data":{"id":1,"name":"张三"}}
         */
        System.out.println(response);
    }
}

@Data
class User {
    private Integer id;
    private String name;

    @Override
    public String toString() {
        return JSON.toJSONString(this);
    }
}

https://www.slideshare.net/randfish/inside-googles-numbers-in-2017?next_slideshow=1

由于json中的key与bean中的属性不能匹配，因此在转换过程中出现了部分属性为null的情况。经过查看官方文档，发现可以使用@JSONField进行解释，但是并没有详细的使用说明。

@JSONField的作用对象:
1. Field
2. Setter 和 Getter方法
注：FastJson在进行操作时，是根据getter和setter的方法进行的，并不是依据Field进行。

一、作用Field
@JSONField作用在Field时，其name不仅定义了输入key的名称，同时也定义了输出的名称。

二、作用在setter和getter方法上
顾名思义，当作用在setter方法上时，就相当于根据 name 到 json中寻找对应的值，并调用该setter对象赋值。
当作用在getter上时，在bean转换为json时，其key值为name定义的值

在fastjson-1.2.12版本中，JSONField支持一个新的配置项jsonDirect，
它的用途是：当你有一个字段是字符串类型，里面是json格式数据，你希望直接输入，而不是经过转义之后再输出。
Model:

import com.alibaba.fastjson.annotation.JSONField;

public static class Model {
    public int id;
    @JSONField(jsonDirect=true)
    public String value;
}

Usage:

Model model = new Model();
model.id = 1001;
model.value = "{}";

String json = JSON.toJSONString(model);
Assert.assertEquals("{\"id\":1001,\"value\":{}}", json);

https://github.com/alibaba/fastjson/wiki/JSONField_jsonDirect_cn
https://github.com/alibaba/fastjson/issues/1244
http://www.cnblogs.com/softidea/p/5681928.html

fastjson 过滤不需要的字段或者只要某些字段

//第一种：在对象响应字段前加注解，这样生成的json也不包含该字段。
@JSONField(serialize=false)
private String name;  

第二种：在对象对应字段前面加transient，表示该字段不用序列化，即在生成json的时候就不会包含该字段了。
private transient  String name;  

transient使用小结
1）一旦变量被transient修饰，变量将不再是对象持久化的一部分，该变量内容在序列化后无法获得访问。
2）transient关键字只能修饰变量，而不能修饰方法和类。注意，本地变量是不能被transient关键字修饰的。变量如果是用户自定义类变量，则该类需要实现Serializable接口。
3）被transient关键字修饰的变量不再能被序列化，一个静态变量不管是否被transient修饰，均不能被序列化。
第三点可能有些人很迷惑，因为发现在User类中的username字段前加上static关键字后，程序运行结果依然不变，即static类型的username也读出来为“Alexia”了，这不与第三点说的矛盾吗？

实际上是这样的：第三点确实没错（一个静态变量不管是否被transient修饰，均不能被序列化），反序列化后类中static型变量username的值为当前JVM中对应static变量的值，这个值是JVM中的不是反序列化得出的

https://www.cnblogs.com/lanxuezaipiao/p/3369962.html

//第三种：使用fastjson的拦截器
PropertyFilter profilter = new PropertyFilter(){  

            @Override
            public boolean apply(Object object, String name, Object value) {
                if(name.equalsIgnoreCase("last")){
                    //false表示last字段将被排除在外
                    return false;
                }
                return true;
            }  

        };
        json = JSON.toJSONString(user, profilter);
        System.out.println(json);   

https://blog.csdn.net/stubbornness1219/article/details/52947013

jackson也是一个很优秀的jackson库，但是如果你因为某些理由想迁移到fastjson，这个指南将会为你介绍如何从jackson迁移到fastjson。

Annotions

在fastjson中，有四个Annotation，JSONType、JSONField、JSONCreator、JSONPOJOBuilder，能够完成jackson大多数Annotation对应的功能。

1. JsonView迁移

在fastjson中，提供有一个LabelFilter，能够实现Jackson JsonView的功能，用于定制序列化。详细文档 https://github.com/alibaba/fastjson/wiki/LabelFilter

2. JsonPOJOBuilder

在Jackson中提供了对Builder模式支持的JsonPOJOBuilder，在fastjson中对应的是JSONPOJOBuilder。详细文档 https://github.com/alibaba/fastjson/wiki/BuilderSupport

3. JsonAnyGetter & JsonAnySetter & JsonUnwrapped

在fastjson 1.2.32版本中引入JSONField.unwrapped配置，支持类似JsonAnyGetter/JsonAnySetter的功能，详细文档 https://github.com/alibaba/fastjson/wiki/JSONField_unwrapped_cn

4. JsonPropertyOrder

在fastjson的JSONType.orders提供了同样的功能。例如：

@JSONType(orders={"name", "id"})
public static class VO {
    public int    id;
    public String name;
}

5. JsonRawValue

在fastjson中，通过JSONField.jsonDirect配置能实现同样的功能。

public static class Model {
    public int id;
    @JSONField(jsonDirect=true)
    public String value;
}

6. JsonSerialize

在fastjson中，可以通过使用JSONField.serializeUsing和JSONType.serializer实现同样的功能。

7. JsonCreator

在fastjson中有对应的JSONCreator

8. JsonSetter

在fastjson中，可以用JSONField实现同样的功能。

9. JsonDeserialize

在fastjson中，可以通过使用JSONField.deserializeUsing和JSONType.deserializer实现同样的功能。

10. JsonIgnoreProperties

在fastjson中，可以通过使用JSONType.ignores实现同样的功能

11. JsonIgnore

在fastjson中，可以通过使用JSONField.serilaize=false和JSONField.deserilaize=false和实现同样的功能

12. JsonFormat

在fastjson中，可以通过使用JSONField.format实现同样的功能

13. Jackson Polymorphic Type Handling Annotations

在fastjson中，可以通过JSONType.seeAlso实现类似的功能。详细文档 https://github.com/alibaba/fastjson/wiki/JSONType_seeAlso_cn

https://github.com/alibaba/fastjson/wiki/guid_to_migrating_from_jackson_to_fastjson_cn

2.4. @JsonRawValue

@JsonRawValue is used to instruct the Jackson to serialize a property exactly as is.

In the following example – we use @JsonRawValue to embed some custom JSON as a value of an entity:

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public class RawBean {     public String name;       @JsonRawValue     public String json; }

The output of serializing the entity is:

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{     "name":"My bean",     "json":{         "attr":false     } }

And a simple test:

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@Test public void whenSerializingUsingJsonRawValue_thenCorrect()   throws JsonProcessingException {        RawBean bean = new RawBean("My bean", "{"attr":false}");       String result = new ObjectMapper().writeValueAsString(bean);     assertThat(result, containsString("My bean"));     assertThat(result, containsString("{"attr":false}")); }

http://www.baeldung.com/jackson-annotations

9.4 日期格式处理

Fastjson能识别下面这么多种日期格式的字符串：

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

private final static String defaultPatttern = "yyyy-MM-dd HH:mm:ss"; private final static DateTimeFormatter defaultFormatter = DateTimeFormatter.ofPattern(defaultPatttern); private final static DateTimeFormatter formatter_dt19_tw = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss"); private final static DateTimeFormatter formatter_dt19_cn = DateTimeFormatter.ofPattern("yyyy年M月d日 HH:mm:ss"); private final static DateTimeFormatter formatter_dt19_cn_1 = DateTimeFormatter.ofPattern("yyyy年M月d日 H时m分s秒"); private final static DateTimeFormatter formatter_dt19_kr = DateTimeFormatter.ofPattern("yyyy년M월d일 HH:mm:ss"); private final static DateTimeFormatter formatter_dt19_us = DateTimeFormatter.ofPattern("MM/dd/yyyy HH:mm:ss"); private final static DateTimeFormatter formatter_dt19_eur = DateTimeFormatter.ofPattern("dd/MM/yyyy HH:mm:ss"); private final static DateTimeFormatter formatter_dt19_de = DateTimeFormatter.ofPattern("dd.MM.yyyy HH:mm:ss"); private final static DateTimeFormatter formatter_dt19_in = DateTimeFormatter.ofPattern("dd-MM-yyyy HH:mm:ss"); private final static DateTimeFormatter formatter_d8 = DateTimeFormatter.ofPattern("yyyyMMdd"); private final static DateTimeFormatter formatter_d10_tw = DateTimeFormatter.ofPattern("yyyy/MM/dd"); private final static DateTimeFormatter formatter_d10_cn = DateTimeFormatter.ofPattern("yyyy年M月d日"); private final static DateTimeFormatter formatter_d10_kr = DateTimeFormatter.ofPattern("yyyy년M월d일"); private final static DateTimeFormatter formatter_d10_us = DateTimeFormatter.ofPattern("MM/dd/yyyy"); private final static DateTimeFormatter formatter_d10_eur = DateTimeFormatter.ofPattern("dd/MM/yyyy"); private final static DateTimeFormatter formatter_d10_de = DateTimeFormatter.ofPattern("dd.MM.yyyy"); private final static DateTimeFormatter formatter_d10_in = DateTimeFormatter.ofPattern("dd-MM-yyyy"); private final static DateTimeFormatter ISO_FIXED_FORMAT = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss").withZone(ZoneId.systemDefault()); private final static String formatter_iso8601_pattern = "yyyy-MM-dd'T'HH:mm:ss"; private final static DateTimeFormatter formatter_iso8601 = DateTimeFormatter.ofPattern(formatter_iso8601_pattern);

默认序列化Date输出使用”yyyy-MM-dd HH:mm:ss”格式，可以用UseISO8601DateFormat特性换成”yyyy-MM-dd’T’HH:mm:ss”格式。

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JSON.defaultTimeZone = TimeZone.getTimeZone("Asia/Shanghai"); JSON.defaultLocale = Locale.US; public static class Model { @JSONField(format = "MMM dd, yyyy h:mm:ss aa") private java.util.Date date; public java.util.Date getDate() { return date; } public void setDate(java.util.Date date) { this.date = date; } @JSONField(format = "MMM-dd-yyyy h:mm:ss aa") public java.sql.Date date2; }

9.5 常见序列化特性的使用

Fastjson的序列化特性定义在枚举类com\alibaba\fastjson\serializer\SerializerFeature.java中，目前正好有30项。
可以通过设置多个特性到FastjsonConfig中全局使用，也可以在某个具体的JSON.writeJSONString时作为参数使用。

1. QuoteFieldNames, //key使用引号
2. UseSingleQuotes, //使用单引号
3. WriteMapNullValue, //输出Map的null值
4. WriteEnumUsingToString, //枚举属性输出toString的结果
5. WriteEnumUsingName, //枚举数据输出name
6. UseISO8601DateFormat, //使用日期格式
7. WriteNullListAsEmpty, //List为空则输出[]
8. WriteNullStringAsEmpty, //String为空则输出””
9. WriteNullNumberAsZero, //Number类型为空则输出0
10. WriteNullBooleanAsFalse, //Boolean类型为空则输出false
11. SkipTransientField,
12. SortField, //排序字段
13. WriteTabAsSpecial,
14. PrettyFormat, // 格式化JSON缩进
15. WriteClassName, // 输出类名
16. DisableCircularReferenceDetect, // 禁止循环引用
17. WriteSlashAsSpecial, // 对斜杠’/’进行转义
18. BrowserCompatible,
19. WriteDateUseDateFormat, // 全局修改日期格式,默认为false。JSON.DEFFAULT_DATE_FORMAT = “yyyy-MM-dd”;JSON.toJSONString(obj, SerializerFeature.WriteDateUseDateFormat);
20. NotWriteRootClassName,
21. DisableCheckSpecialChar,
22. BeanToArray,
23. WriteNonStringKeyAsString,
24. NotWriteDefaultValue,
25. BrowserSecure,
26. IgnoreNonFieldGetter,
27. WriteNonStringValueAsString,
28. IgnoreErrorGetter,
29. WriteBigDecimalAsPlain,
30. MapSortField

使用示例如下（可以参见此处）：

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Word word = new Word(); word.setA("a"); word.setB(2); word.setC(true); word.setD("d"); word.setE(""); word.setF(null); word.setDate(new Date()); System.out.println(JSON.toJSONString(word)); System.out.println(JSON.toJSONString(word, SerializerFeature.PrettyFormat, SerializerFeature.WriteMapNullValue, SerializerFeature.WriteNullStringAsEmpty, SerializerFeature.DisableCircularReferenceDetect, SerializerFeature.WriteNullListAsEmpty));

9.6 Annotation注解的使用

1) JSONField

可以配置在属性（setter、getter）和字段（必须是public field）上。
详情参见此处：JSONField用法

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

package com.alibaba.fastjson.annotation; public @interface JSONField { // 配置序列化和反序列化的顺序，1.1.42版本之后才支持 int ordinal() default 0; // 指定字段的名称 String name() default ""; // 指定字段的格式，对日期格式有用 String format() default ""; // 是否序列化 boolean serialize() default true; // 是否反序列化 boolean deserialize() default true; }

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

@JSONField(name="ID") public int getId() {return id;} // 配置date序列化和反序列使用yyyyMMdd日期格式 @JSONField(format="yyyyMMdd") public Date date1; // 不序列化 @JSONField(serialize=false) public Date date2; // 不反序列化 @JSONField(deserialize=false) public Date date3; // 按ordinal排序 @JSONField(ordinal = 2) private int f1; @JSONField(ordinal = 1) private int f2;

http://kimmking.github.io/2017/06/06/json-best-practice/

7. fastjson序列化的需要像json-lib一样配置java bean的序列化么？

不需要，fastjson的序列化和反序列化都不需要做特别配置，唯一的要求是，你序列化的类符合java bean规范。

8. fastjson如何处理日期

fastjson处理日期的API很简单，例如：

JSON.toJSONStringWithDateFormat(date, "yyyy-MM-dd HH:mm:ss.SSS")

使用ISO-8601日期格式

JSON.toJSONString(obj, SerializerFeature.UseISO8601DateFormat);

全局修改日期格式

JSON.DEFFAULT_DATE_FORMAT = "yyyy-MM-dd";
JSON.toJSONString(obj, SerializerFeature.WriteDateUseDateFormat);

反序列化能够自动识别如下日期格式：

• ISO-8601日期格式
• yyyy-MM-dd
• yyyy-MM-dd HH:mm:ss
• yyyy-MM-dd HH:mm:ss.SSS
• 毫秒数字
• 毫秒数字字符串
• .NET JSON日期格式
• new Date(198293238)

11. IE 6不支持JSON带中文字符串，要怎么处理？

fastjson提供了BrowserCompatible这个配置，打开之后，所有的中文都会序列化为\uXXXX这种格式，字节数会多一些，但是能兼容IE 6。

String  jsonString = JSON.toJSONString(obj, SerializerFeature.BrowserCompatible);

10. 当对象存在引用时，序列化后的结果浏览器不支持，怎么办？

使用SerializerFeature.DisableCircularReferenceDetect特性关闭引用检测和生成。
例如：

String  jsonString = JSON.toJSONString(obj, SerializerFeature.DisableCircularReferenceDetect);

https://github.com/alibaba/fastjson/wiki/%E5%B8%B8%E8%A7%81%E9%97%AE%E9%A2%98

做个分析 FastJson 在使用 toJSONString 会使用 写入操作，而 我的类里面有这样一个方法 public int getLengthOfByte()
这样FastJson 就会认为 这个类 有一个 lengthOfByte 的属性，于是就出现了异常，解决方法

@JSONType(ignores = "lengthOfByte")
public class DRMessageBody {

  public int getLengthOfByte(){
        String json = toJson();
        int num = -1;
        num = json.getBytes().length;
        if(num==-1){
            new RuntimeException("Messagebody of json length is error!");
        }
        return num;
    }
}

https://www.jianshu.com/p/f96e257c7682