fast json详解二

• 通过maven引入相应的json包

    <dependencies>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.49</version>
        </dependency>
    </dependencies>

• 定义一个需要转换所实体类User，代码如下：

package com.ivan.json.entity;

import java.util.Date;

import com.alibaba.fastjson.annotation.JSONField;

public class User {

    private Long   id;

    private String name;

    @JSONField(format = "yyyy-MM-dd HH:mm:ss")
    private Date   createTime;

    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;
    }

    public Date getCreateTime() {
        return createTime;
    }

    public void setCreateTime(Date createTime) {
        this.createTime = createTime;
    }
    
}

1. 写个简单的测试类用于测试fastjson的序列化与反序列化，代码如下：

package com.ivan.json;

import java.util.Date;

import com.alibaba.fastjson.JSON;
import com.ivan.json.entity.User;

public class SimpleTest {

    public static void main(String[] args) {
        serialize();
        deserialize();
    }

    public static void serialize() {
        User user = new User();
        user.setId(11L);
        user.setName("西安");
        user.setCreateTime(new Date());
        String jsonString = JSON.toJSONString(user);
        System.out.println(jsonString);
    }

    public static void deserialize() {
        String jsonString = "{"createTime":"2018-08-17 14:38:38","id":11,"name":"西安"}";
        User user = JSON.parseObject(jsonString, User.class);
        System.out.println(user.getName());
        System.out.println(user.getCreateTime());
    }
}

• fastjson通过SerializerFeature对生成的json格式的数据进行一些定制，比如可以输入的格式更好看，使用单引号而非双引号等。例子程序如下：

package com.ivan.json;

import java.util.Date;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.serializer.SerializerFeature;
import com.ivan.json.entity.User;

public class SerializerFeatureTest {

    public static void main(String[] args) {
        User user = new User();
        user.setId(11L);
        user.setCreateTime(new Date());
        String jsonString = JSON.toJSONString(user, SerializerFeature.PrettyFormat, 
                SerializerFeature.WriteNullStringAsEmpty, SerializerFeature.UseSingleQuotes);
        System.out.println(jsonString);

    }

}

• SerializerFeature常用属性

• JSONField与JSONType注解的使用

package com.alibaba.fastjson.annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import com.alibaba.fastjson.parser.Feature;
import com.alibaba.fastjson.serializer.SerializerFeature;

@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.METHOD, ElementType.FIELD, ElementType.PARAMETER })
public @interface JSONField {
// 配置序列化和反序列化的顺序
    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;
//字段级别的SerializerFeature
    SerializerFeature[] serialzeFeatures() default {};
//
    Feature[] parseFeatures() default {};
   //给属性打上标签， 相当于给属性进行了分组
    String label() default "";
    
    boolean jsonDirect() default false;
    
//制定属性的序列化类
    Class<?> serializeUsing() default Void.class;
 //制定属性的反序列化类
    Class<?> deserializeUsing() default Void.class;

    String[] alternateNames() default {};

    boolean unwrapped() default false;
}

其中serializeUsing与deserializeUsing可以用于对字段的序列化与反序列化进行定制化。比如我们在User实体上加上个sex属性，类型为boolean。下面分别定义了序列化类与反序列化类，序列化类代码如下：

package com.ivan.json.converter;

import java.io.IOException;
import java.lang.reflect.Type;

import com.alibaba.fastjson.serializer.JSONSerializer;
import com.alibaba.fastjson.serializer.ObjectSerializer;

public class SexSerializer implements ObjectSerializer {

    public void write(JSONSerializer serializer,
                      Object object,
                      Object fieldName,
                      Type fieldType,
                      int features)
            throws IOException {
        Boolean value = (Boolean) object;
        String text = "女";
        if (value != null && value == true) {
            text = "男";
        }
        serializer.write(text);
    }

}

 反序列化类代码如下：

package com.ivan.json.converter;

import java.lang.reflect.Type;


import com.alibaba.fastjson.parser.DefaultJSONParser;
import com.alibaba.fastjson.parser.JSONToken;
import com.alibaba.fastjson.parser.deserializer.ObjectDeserializer;

public class SexDeserialize implements ObjectDeserializer {

    public <T> T deserialze(DefaultJSONParser parser,
                                        Type type,
                                        Object fieldName) {
        


        String sex = parser.parseObject(String.class);
        if ("男".equals(sex)) {
            return (T) Boolean.TRUE;
        } else {
            return (T) Boolean.FALSE;
        }
    }

    public int getFastMatchToken() {
        return JSONToken.UNDEFINED;
    }

}

fastjosn提供了JSONType用于类级别的定制化, JSONType的源码如下：

package com.alibaba.fastjson.annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import com.alibaba.fastjson.PropertyNamingStrategy;
import com.alibaba.fastjson.parser.Feature;
import com.alibaba.fastjson.serializer.SerializeFilter;
import com.alibaba.fastjson.serializer.SerializerFeature;

@Retention(RetentionPolicy.RUNTIME)
//需要标注在类上
@Target({ ElementType.TYPE })
public @interface JSONType {

    boolean asm() default true;
//这里可以定义输出json的字段顺序
    String[] orders() default {};
//包含的字段
    String[] includes() default {};
//不包含的字段
    String[] ignores() default {};
//类级别的序列化特性定义
    SerializerFeature[] serialzeFeatures() default {};
    Feature[] parseFeatures() default {};
    //按字母顺序进行输出
    boolean alphabetic() default true;
    
    Class<?> mappingTo() default Void.class;
    
    Class<?> builder() default Void.class;
    
    String typeName() default "";

    String typeKey() default "";
    
    Class<?>[] seeAlso() default{};
    //序列化类
    Class<?> serializer() default Void.class;
    //反序列化类
    Class<?> deserializer() default Void.class;

    boolean serializeEnumAsJavaBean() default false;

    PropertyNamingStrategy naming() default PropertyNamingStrategy.CamelCase;

    Class<? extends SerializeFilter>[] serialzeFilters() default {};
}

• PropertyFilter 根据PropertyName和PropertyValue来判断是否序列化,接口定义如下：

package com.alibaba.fastjson.serializer;

/**
 * @author wenshao[szujobs@hotmail.com]
 */
public interface PropertyFilter extends SerializeFilter {

    /**
     * @param object the owner of the property
     * @param name the name of the property
     * @param value the value of the property
     * @return true if the property will be included, false if to be filtered out
    * 根据 属性的name与value判断是否进行序列化
     */
    boolean apply(Object object, String name, Object value);
}

• PropertyPreFilter根据PropertyName判断是否序列化

package com.alibaba.fastjson.serializer;

public interface PropertyPreFilter extends SerializeFilter {

//根据 object与name判断是否进行序列化
    boolean apply(JSONSerializer serializer, Object object, String name);
}

• NameFilter 序列化时修改Key

package com.alibaba.fastjson.serializer;

public interface NameFilter extends SerializeFilter {
//根据 name与value的值，返回json字段key的值
    String process(Object object, String name, Object value);
}

• ValueFilter 序列化时修改Value

package com.alibaba.fastjson.serializer;

public interface ValueFilter extends SerializeFilter {
  //根据name与value定制输出json的value
    Object process(Object object, String name, Object value);
}

• BeforeFilter 在序列化对象的所有属性之前执行某些操作

package com.alibaba.fastjson.serializer;

public abstract class BeforeFilter implements SerializeFilter {

    private static final ThreadLocal<JSONSerializer> serializerLocal = new ThreadLocal<JSONSerializer>();
    private static final ThreadLocal<Character>      seperatorLocal  = new ThreadLocal<Character>();

    private final static Character                   COMMA           = Character.valueOf(',');

    final char writeBefore(JSONSerializer serializer, Object object, char seperator) {
        serializerLocal.set(serializer);
        seperatorLocal.set(seperator);
        writeBefore(object);
        serializerLocal.set(null);
        return seperatorLocal.get();
    }

    protected final void writeKeyValue(String key, Object value) {
        JSONSerializer serializer = serializerLocal.get();
        char seperator = seperatorLocal.get();
        serializer.writeKeyValue(seperator, key, value);
        if (seperator != ',') {
            seperatorLocal.set(COMMA);
        }
    }
//需要实现的方法，在实际实现中可以调用writeKeyValue增加json的内容
    public abstract void writeBefore(Object object);
}

• AfterFilter 在序列化对象的所有属性之后执行某些操作

package com.alibaba.fastjson.serializer;

/**
 * @since 1.1.35
 */
public abstract class AfterFilter implements SerializeFilter {

    private static final ThreadLocal<JSONSerializer> serializerLocal = new ThreadLocal<JSONSerializer>();
    private static final ThreadLocal<Character>      seperatorLocal  = new ThreadLocal<Character>();

    private final static Character                   COMMA           = Character.valueOf(',');

    final char writeAfter(JSONSerializer serializer, Object object, char seperator) {
        serializerLocal.set(serializer);
        seperatorLocal.set(seperator);
        writeAfter(object);
        serializerLocal.set(null);
        return seperatorLocal.get();
    }

    protected final void writeKeyValue(String key, Object value) {
        JSONSerializer serializer = serializerLocal.get();
        char seperator = seperatorLocal.get();
        serializer.writeKeyValue(seperator, key, value);
        if (seperator != ',') {
            seperatorLocal.set(COMMA);
        }
    }
//子类需要实现的方法，实际使用的时候可以调用writeKeyValue增加内容
    public abstract void writeAfter(Object object);
}

• LabelFilter根据 JsonField配置的label来判断是否进行输出

package com.alibaba.fastjson.serializer;

//根据 JsonField配置的label来判断是否进行输出
public interface LabelFilter extends SerializeFilter {
    boolean apply(String label);
}

泛型反序列化

fastjson通过TypeReference来实现泛型的反序列化，以下是一个简单的例子程序。首先定义了BaseDTO用于所有DTO的父类，代码如下：

package com.ivan.frame.dto.common;

import java.io.Serializable;

import com.alibaba.fastjson.JSONObject;

public class BaseDTO implements Serializable{

    private static final long  serialVersionUID = 2230553030766621644L;

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

}

RequestDTO用于抽像所有的请求DTO，里面有个泛型参数，代码如下：

package com.ivan.frame.dto.common;


public final class RequestDTO<T extends BaseDTO> extends BaseDTO {

    private static final long serialVersionUID = -2780042604928728379L;

    /**
     * 调用方的名称
     */
    private String            caller;

    /**
     * 请求参数
     */
    private T                 param;
    

 
    public String getCaller() {
        return caller;
    }

    public void setCaller(String caller) {
        this.caller = caller;
    }

    /**
     * 获取请求参数
     */
    public T getParam() {
        return param;
    }

    /**
     * 设置请求参数
     * 
     * @param param 请求参数
     */
    public void setParam(T param) {
        this.param = param;
    }

}

定义一个具体的业务对象， PersonDTO代码如下：

package com.ivan.frame.dto;

import com.ivan.frame.dto.common.BaseDTO;

public class PersonDTO extends BaseDTO {
    
    private static final long serialVersionUID = 4637634512292751986L;
    
    private int id;
    private int age;
    private String name;
    
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    
}

通过JSON.parseObject传入TypeReference对象进行泛型转换，代码如下：

package com.ivan.json;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.TypeReference;
import com.ivan.frame.dto.PersonDTO;
import com.ivan.frame.dto.common.RequestDTO;

public class GenericTest {

    public static void main(String[] args) {
        RequestDTO<PersonDTO> requestDTO = new RequestDTO<PersonDTO>();
        requestDTO.setCaller("callerId");
        PersonDTO personDTO = new PersonDTO();
        personDTO.setAge(11);
        personDTO.setName("张三");
        requestDTO.setParam(personDTO);
        
        String jsonString = JSON.toJSONString(requestDTO);
        System.out.println(jsonString);
        //这行是关键代码
        requestDTO = JSON.parseObject(jsonString, new TypeReference<RequestDTO<PersonDTO>>(){});
        
        
        System.out.println(requestDTO.getParam().getName());
    }
}

fastjson各种概念

• SerializeConfig：内部是个map容器主要功能是配置并记录每种Java类型对应的序列化类。
• SerializeWriter 继承自Java的Writer，其实就是个转为FastJSON而生的StringBuilder，完成高性能的字符串拼接。
• SerializeFilter: 用于对对象的序列化实现各种定制化的需求。
• SerializerFeature：对于对输出的json做各种格式化的需求。
• JSONSerializer：相当于一个序列化组合器，集成了SerializeConfig， SerializeWriter ， SerializeFilter与SerializerFeature。

序列化的入口代码如下，上面提到的各种概念都包含了

    public static String toJSONString(Object object, // 
                                      SerializeConfig config, // 
                                      SerializeFilter[] filters, // 
                                      String dateFormat, //
                                      int defaultFeatures, // 
                                      SerializerFeature... features) {
        SerializeWriter out = new SerializeWriter(null, defaultFeatures, features);

        try {
            JSONSerializer serializer = new JSONSerializer(out, config);
            
            if (dateFormat != null && dateFormat.length() != 0) {
                serializer.setDateFormat(dateFormat);
                serializer.config(SerializerFeature.WriteDateUseDateFormat, true);
            }

            if (filters != null) {
                for (SerializeFilter filter : filters) {
                    serializer.addFilter(filter);
                }
            }

            serializer.write(object);

            return out.toString();
        } finally {
            out.close();
        }
    }

 反序列化相关的概念

• ParserConfig：内部通过一个map保存各种ObjectDeserializer。
• JSONLexer : 与SerializeWriter相对应，用于解析json字符串。
• JSONToken：定义了一系统的特殊字符，这些称为token。
• ParseProcess ：定制反序列化，类似于SerializeFilter。
• Feature：用于定制各种反序列化的特性。
• DefaultJSONParser：相当于反序列化组合器，集成了ParserConfig，Feature， JSONLexer 与ParseProcess。

反序列化的入口代码如下，上面的概念基本都包含了：

    @SuppressWarnings("unchecked")
    public static <T> T parseObject(String input, Type clazz, ParserConfig config, ParseProcess processor,
                                          int featureValues, Feature... features) {
        if (input == null) {
            return null;
        }

        if (features != null) {
            for (Feature feature : features) {
                featureValues |= feature.mask;
            }
        }

        DefaultJSONParser parser = new DefaultJSONParser(input, config, featureValues);

        if (processor != null) {
            if (processor instanceof ExtraTypeProvider) {
                parser.getExtraTypeProviders().add((ExtraTypeProvider) processor);
            }

            if (processor instanceof ExtraProcessor) {
                parser.getExtraProcessors().add((ExtraProcessor) processor);
            }

            if (processor instanceof FieldTypeResolver) {
                parser.setFieldTypeResolver((FieldTypeResolver) processor);
            }
        }

        T value = (T) parser.parseObject(clazz, null);

        parser.handleResovleTask(value);

        parser.close();

        return (T) value;
    }

 与Spring MVC整合

fastjson提供了FastJsonHttpMessageConverter用于将Spring mvc里的body数据(必须是json格式)转成Controller里的请求参数或者将输出的对象转成json格式的数据。spring mvc里的核心配置如下：

    <mvc:annotation-driven conversion-service="conversionService">
        <mvc:message-converters register-defaults="true">
            <bean
                class="com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter">
                <property name="supportedMediaTypes">
                    <list>
                        <value>text/html;charset=UTF-8</value>
                        <value>application/json;charset=UTF-8</value>
                    </list>
                </property>
                <property name="features">
                    <array>
                        <value>WriteMapNullValue</value>
                        <value>WriteNullStringAsEmpty</value>
                    </array>
                </property>
            </bean>
        </mvc:message-converters>
    </mvc:annotation-driven>

这里有一个注意点，当你用Spring 3或者fastjson使用的是1.1.x的版本，在转换带有泛型参数类型的时候无法进行转换，而在Spring4配合fastjson1.2.X的版本可以解决这个问题。FastJsonHttpMessageConverter read的核心代码如下：

public class FastJsonHttpMessageConverter extends AbstractHttpMessageConverter<Object>//
        implements GenericHttpMessageConverter<Object> {

//将json转成javabean的时候会调用。这里的type
    public Object read(Type type, //
                       Class<?> contextClass, //
                       HttpInputMessage inputMessage //
    ) throws IOException, HttpMessageNotReadableException {
        return readType(getType(type, contextClass), inputMessage);
    }

//这里会通过Spring4TypeResolvableHelper得到类型参数，
    protected Type getType(Type type, Class<?> contextClass) {
        if (Spring4TypeResolvableHelper.isSupport()) {
            return Spring4TypeResolvableHelper.getType(type, contextClass);
        }

        return type;
    }

}