FastJson对复杂的泛型对象的解析问题

秒速五厘米 2022-05-22 22:20 413阅读 0赞

首先要说的是FastJson提供了一个用于处理泛型反序列化的类[TypeReference][],在知道具体泛型类型的情况下可以实现反序列化，这里由于应用场景不适用不对其进行讨论。

如下场景：

public class PieChartVO<T extends BaseDebtVO> implements Serializable {
       
    
    	private static final long serialVersionUID = -6422895776727574355L;
    
    	private BigDecimal avgYearRate;
    	
    	private ArrayList<T> transVOs;
    
    	public BigDecimal getAvgYearRate() {
       
    		return avgYearRate;
    	}
    
    	public void setAvgYearRate(BigDecimal avgYearRate) {
       
    		this.avgYearRate = avgYearRate;
    	}
    
    	public ArrayList<T> getTransVOs() {
       
    		return transVOs;
    	}
    
    	public void setTransVOs(ArrayList<T> transVOs) {
       
    		this.transVOs = transVOs;
    	}
    }

public class CreditorDebtVO extends BaseDebtVO {
       
    
    	private static final long serialVersionUID = -254172337494852158L;
    
    	private BigDecimal totalEarning;
    
    	public BigDecimal getTotalEarning() {
       
    		return totalEarning;
    	}
    
    	public void setTotalEarning(BigDecimal totalEarning) {
       
    		this.totalEarning = totalEarning;
    	}
    
    }

public class ObligorDebtVO extends BaseDebtVO {
       
    
        private static final long serialVersionUID = 3314361571700869005L;
    
        private Integer overdueCount;
    
        private BigDecimal overdueOtherFee;
    
        public Integer getOverdueCount() {
       
            return overdueCount;
        }
    
        public void setOverdueCount(Integer overdueCount) {
       
            this.overdueCount = overdueCount;
        }
    
        public BigDecimal getOverdueOtherFee() {
       
            return overdueOtherFee;
        }
    
        public void setOverdueOtherFee(BigDecimal overdueOtherFee) {
       
            this.overdueOtherFee = overdueOtherFee;
        }
    }

{
       
        "body": {
       
            "avgYearRate": 14.8, 
            "transVOs": [
                {
       
                    "avgRate": 19.2, 
                    "cleanCount": 8, 
                    "id": 15, 
                    "subTitle": "aaa", 
                    "title": "bbb", 
                    "totalEarning": 20.75, 
                    "totalPrincipal": 17000, 
                    "transCount": 3, 
                    "transMoney": 4698.93, 
                    "transOverdueMoney": 0
                }
            ]
        }, 
        "result": 1
    }

对于获取到的json数据并不知道具体的泛型类型，也就没法指定的情况下，解决方案是对反序列化进行自定义定制，fastJson自身对基础的field内置了许多反序列化器，当对json反序列化时，会根据filed的class找到相应的反序列化器来执行反序列化。

public class ParserConfig {
       
    
        private final IdentityHashMap<Type, ObjectDeserializer> deserializers = new IdentityHashMap<Type, ObjectDeserializer>();
    
        /**省略了其他代码*/
        private void initDeserializers() {
       
            deserializers.put(SimpleDateFormat.class, MiscCodec.instance);
            deserializers.put(java.sql.Timestamp.class, SqlDateDeserializer.instance_timestamp);
            deserializers.put(java.sql.Date.class, SqlDateDeserializer.instance);
            deserializers.put(java.sql.Time.class, TimeDeserializer.instance);
            deserializers.put(java.util.Date.class, DateCodec.instance);
            deserializers.put(Calendar.class, CalendarCodec.instance);
            deserializers.put(XMLGregorianCalendar.class, CalendarCodec.instance);
    
            deserializers.put(JSONObject.class, MapDeserializer.instance);
            deserializers.put(JSONArray.class, CollectionCodec.instance);
    
            deserializers.put(Map.class, MapDeserializer.instance);
            deserializers.put(HashMap.class, MapDeserializer.instance);
            deserializers.put(LinkedHashMap.class, MapDeserializer.instance);
            deserializers.put(TreeMap.class, MapDeserializer.instance);
            deserializers.put(ConcurrentMap.class, MapDeserializer.instance);
            deserializers.put(ConcurrentHashMap.class, MapDeserializer.instance);
    
            deserializers.put(Collection.class, CollectionCodec.instance);
            deserializers.put(List.class, CollectionCodec.instance);
            deserializers.put(ArrayList.class, CollectionCodec.instance);
    
            deserializers.put(Object.class, JavaObjectDeserializer.instance);
            deserializers.put(String.class, StringCodec.instance);
            deserializers.put(StringBuffer.class, StringCodec.instance);
            deserializers.put(StringBuilder.class, StringCodec.instance);
            deserializers.put(char.class, CharacterCodec.instance);
            deserializers.put(Character.class, CharacterCodec.instance);
            deserializers.put(byte.class, NumberDeserializer.instance);
            deserializers.put(Byte.class, NumberDeserializer.instance);
            deserializers.put(short.class, NumberDeserializer.instance);
            deserializers.put(Short.class, NumberDeserializer.instance);
            deserializers.put(int.class, IntegerCodec.instance);
            deserializers.put(Integer.class, IntegerCodec.instance);
            deserializers.put(long.class, LongCodec.instance);
            deserializers.put(Long.class, LongCodec.instance);
            deserializers.put(BigInteger.class, BigIntegerCodec.instance);
            deserializers.put(BigDecimal.class, BigDecimalCodec.instance);
            deserializers.put(float.class, FloatCodec.instance);
            deserializers.put(Float.class, FloatCodec.instance);
            deserializers.put(double.class, NumberDeserializer.instance);
            deserializers.put(Double.class, NumberDeserializer.instance);
            deserializers.put(boolean.class, BooleanCodec.instance);
            deserializers.put(Boolean.class, BooleanCodec.instance);
            deserializers.put(Class.class, MiscCodec.instance);
            deserializers.put(char[].class, new CharArrayCodec());
    
            deserializers.put(AtomicBoolean.class, BooleanCodec.instance);
            deserializers.put(AtomicInteger.class, IntegerCodec.instance);
            deserializers.put(AtomicLong.class, LongCodec.instance);
            deserializers.put(AtomicReference.class, ReferenceCodec.instance);
    
            deserializers.put(WeakReference.class, ReferenceCodec.instance);
            deserializers.put(SoftReference.class, ReferenceCodec.instance);
    
            deserializers.put(UUID.class, MiscCodec.instance);
            deserializers.put(TimeZone.class, MiscCodec.instance);
            deserializers.put(Locale.class, MiscCodec.instance);
            deserializers.put(Currency.class, MiscCodec.instance);
            deserializers.put(InetAddress.class, MiscCodec.instance);
            deserializers.put(Inet4Address.class, MiscCodec.instance);
            deserializers.put(Inet6Address.class, MiscCodec.instance);
            deserializers.put(InetSocketAddress.class, MiscCodec.instance);
            deserializers.put(File.class, MiscCodec.instance);
            deserializers.put(URI.class, MiscCodec.instance);
            deserializers.put(URL.class, MiscCodec.instance);
            deserializers.put(Pattern.class, MiscCodec.instance);
            deserializers.put(Charset.class, MiscCodec.instance);
            deserializers.put(JSONPath.class, MiscCodec.instance);
            deserializers.put(Number.class, NumberDeserializer.instance);
            deserializers.put(AtomicIntegerArray.class, AtomicCodec.instance);
            deserializers.put(AtomicLongArray.class, AtomicCodec.instance);
            deserializers.put(StackTraceElement.class, StackTraceElementDeserializer.instance);
    
            deserializers.put(Serializable.class, JavaObjectDeserializer.instance);
            deserializers.put(Cloneable.class, JavaObjectDeserializer.instance);
            deserializers.put(Comparable.class, JavaObjectDeserializer.instance);
            deserializers.put(Closeable.class, JavaObjectDeserializer.instance);
    
            deserializers.put(JSONPObject.class, new JSONPDeserializer());
        }
    
        public ObjectDeserializer getDeserializer(Class<?> clazz, Type type) {
       
            /** 首先从内部已经注册查找特定type的反序列化实例 */
            ObjectDeserializer derializer = deserializers.get(type);
            if (derializer != null) {
       
                return derializer;
            }
    	.......
        }
    
    }

可以看到对于ArrayList的默认的反序列化器是CollectionCodec，另外fastjson还提供了@JSONField注解对field可以有一些自定义的处理，其deserializeUsing属性可以指定具体的反序列化器。我们要做的就很简单了。

自定义反序列化器实现CollectionCodec，具体的反序列化工作仍然交由CollectionCodec处理，只不过须要对得到的对象进行自定义的加工。这里通过判断某个field是否存在来决定以哪个类来反序列化。

public class DebtVODeserializer extends CollectionCodec {
       
        @Override
        public <T> T deserialze(DefaultJSONParser parser, Type type, Object fieldName) {
       
            T list = super.deserialze(parser, type, fieldName);
            JSONArray jsonArray = JSON.parseArray(JSON.toJSONString(list));
            ArrayList<CreditorDebtVO> debtVOs = new ArrayList<>();
            if (jsonArray != null && jsonArray.size()>0){
       
                if (jsonArray.getJSONObject(0).get("totalEarning")!=null){
       
                    ArrayList<CreditorDebtVO> creditorDebtVOList = (ArrayList<CreditorDebtVO>)JSON.parseArray(JSON.toJSONString(list),CreditorDebtVO.class);
                    return (T)creditorDebtVOList;
                } else if (jsonArray.getJSONObject(0).get("overdueOtherFee")!=null){
       
                    ArrayList<ObligorDebtVO> obligorDebtVOList = (ArrayList<ObligorDebtVO>)JSON.parseArray(JSON.toJSONString(list),ObligorDebtVO.class);
                    return (T)obligorDebtVOList;
                }
            } else {
       
                return list;
            }
    
            return (T)debtVOs;
        }
    }

修改PieChartVO，指定自定义的反序列化器

@JSONField(deserializeUsing = DebtVODeserializer.class)
    	public void setTransVOs(ArrayList<T> transVOs) {
       
    		this.transVOs = transVOs;
    	}

PieChartVO vo = JSON.parseObject(json,PieChartVO.class);

如上，直接反序列化即可，对于使用方而言，不需要判断用哪个类来反序列化，代码上看简洁了许多...

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