public static final String toJSONString(Object object, SerializerFeature... features) {
        SerializeWriter out = new SerializeWriter();
        try {
            JSONSerializer serializer = new JSONSerializer(out);
            for (com.alibaba.fastjson.serializer.SerializerFeature feature : features) {
                serializer.config(feature, true);
            }
            serializer.write(object);
            return out.toString();
        } finally {
            out.close();
        }
    }

演示程序

import com.alibaba.fastjson.JSONObject;
import com.alibaba.fastjson.serializer.SerializerFeature;
import com.alibaba.fastjson.support.spring.PropertyPreFilters;
/**
 * 使用FastJson將實(shí)體對(duì)象轉(zhuǎn)換成Json字符串測(cè)試類
 */
public class FastJsonApplication {
     public static void main(String[] args) {
        User user = new User();
        user.setId(1L);
        user.setUsername("張三");
        user.setPassword("");
        user.setMobile(null);
        user.setCountry("中國(guó)");
        user.setCity("武漢");
     String jsonUser = null;
        /**
         * 指定排除屬性過濾器和包含屬性過濾器
         * 指定排除屬性過濾器：轉(zhuǎn)換成JSON字符串時(shí)，排除哪些屬性
         * 指定包含屬性過濾器：轉(zhuǎn)換成JSON字符串時(shí)，包含哪些屬性
         */
        String[] excludeProperties = {"country", "city"};
        String[] includeProperties = {"id", "username", "mobile"};
        PropertyPreFilters filters = new PropertyPreFilters();
        PropertyPreFilters.MySimplePropertyPreFilter excludefilter = filters.addFilter();
        excludefilter.addExcludes(excludeProperties);
        PropertyPreFilters.MySimplePropertyPreFilter includefilter = filters.addFilter();
        includefilter.addIncludes(includeProperties);
        /**
         * 情況一：默認(rèn)忽略值為null的屬性
         */
        jsonUser = JSONObject.toJSONString(user, SerializerFeature.PrettyFormat);
        System.out.println("情況一:\n" + jsonUser);
        /**
         * 情況二：包含值為null的屬性
         */
        jsonUser = JSONObject.toJSONString(user, SerializerFeature.PrettyFormat, SerializerFeature.WriteMapNullValue);
        System.out.println("情況二:\n" + jsonUser);
        /**
         * 情況三：默認(rèn)忽略值為null的屬性，但是排除country和city這兩個(gè)屬性
         */
        jsonUser = JSONObject.toJSONString(user, excludefilter, SerializerFeature.PrettyFormat);
        System.out.println("情況三:\n" + jsonUser);
        /**
         * 情況四：包含值為null的屬性，但是排除country和city這兩個(gè)屬性
         */
        jsonUser = JSONObject.toJSONString(user, excludefilter, SerializerFeature.PrettyFormat, SerializerFeature.WriteMapNullValue);
        System.out.println("情況四:\n" + jsonUser);
        /**
         * 情況五：默認(rèn)忽略值為null的屬性，但是包含id、username和mobile這三個(gè)屬性
         */
        jsonUser = JSONObject.toJSONString(user, includefilter, SerializerFeature.PrettyFormat);
        System.out.println("情況五:\n" + jsonUser);
        /**
         * 情況六：包含值為null的屬性，但是包含id、username和mobile這三個(gè)屬性
         */
        jsonUser = JSONObject.toJSONString(user, includefilter, SerializerFeature.PrettyFormat, SerializerFeature.WriteMapNullValue);
        System.out.println("情況六:\n" + jsonUser);
    }
    /**
     * 用戶實(shí)體類
     */
    public static class User {  
        private Long id;
        private String username;
        private String password;
        private String mobile;
        private String country;
        private String city;
    //此處省略了相應(yīng)屬性的set、get方法
}

運(yùn)行結(jié)果：

結(jié)果說明：

情況一和情況二說明了public static String toJSONString(Object object, SerializeFilter filter, SerializerFeature… features)這個(gè)方法將實(shí)體對(duì)象轉(zhuǎn)換成JSON字符串時(shí)，默認(rèn)是忽略掉值為null的屬性，并且說明了如何使得轉(zhuǎn)換后的JSON字符串包含值為null的屬性。
情況三和情況四說明了如何使用SerializeFilter來排除指定屬性，使得轉(zhuǎn)換后的JSON字符串中不包含這些屬性。
情況五和情況六說明了如何使用SerializeFilter來包含指定屬性，使得轉(zhuǎn)換后的JSON字符串中只包含這些屬性。

JSONObject toJSONString 遇到的坑

引入pom文件

  <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.73</version>
            <scope>test</scope>
        </dependency>

使用JSONObject 輸出 int類型的map

是非json格式

import java.util.HashMap;
import java.util.Map;
import com.alibaba.fastjson.JSONObject;
public class JsonTest {
    public static void main(String[] args) {
        Map<Integer, String> map = new HashMap<>();
        map.put(1, "aaasa");
        map.put(2, "bbbbb");
        map.put(3, "ccccc");
        map.put(4, "ddddd");
        map.put(5, "eeeee");
        System.out.println(JSONObject.toJSONString(map));
    }
}

輸出結(jié)果