【安全研究】Jackson 学习笔记

2023年3月23日02:38:58评论23 views字数 17983阅读59分56秒阅读模式

基本介绍

Jackson框架是基于Java平台的一套数据处理工具，被称为"最好的Java Json解析器"，目前Jackson主要有1.x和2.x两个分支版本，其中1.x的类库中包命名以org.codehaus.jackson.xxx开头，2.x类库中包命令com.fastxml.jackson.xxx开头，Jackson框架包含以下3个核心库：

streaming
databind
annotations.Jackson

解析处理

ObjectMapper是Jackson库的主要类，它可以将JSON数据转换成Java对象或者将JAVA对象序列化为JSON数据，ObjectMapper通过JsonParser和JsonGenerator的实例实现JSON实际的读/写

类声明

org.codehaus.jackson.map.ObjectMapper类的声明如下：

public class ObjectMapper   extends ObjectCodec      implements Versioned

嵌套类

static class ObjectMapper.DefaultTypeResolverBuilder：定制TypeResolverBuilder，提供所谓的"默认输入"使用类型解析构建器

构造函数

ObjectMapper()：默认的构造函数，使用StdSerializerProvider作为其SerializerProvider，并使用BeanSerializerFactory作为其SerializerFactory
ObjectMapper(JsonFactory jf)：使用指定的JsonFactory构建必要的JsonParsers和/或JsonGenerators映射
ObjectMapper(JsonFactory jf, SerializerProvider sp, DeserializerProvider dp)
ObjectMapper(JsonFactory jf, SerializerProvider sp, DeserializerProvider dp, SerializationConfig sconfig, DeserializationConfig dconfig)
ObjectMapper(SerializerFactory sf)：可以设置序列化工厂setSerializerFactory(org.codehaus.jackson.map.SerializerFactory）

继承的方法

ObjectMapper类继承了java.lang.Objec类方法

数据处理

Json处理方法分类

Jackson支持Java对象与Json之间的相互转化，Java对象序列化为Json字符串，Json字符串也可以反序列化为相同的Java对象，Jackson提供了三种可选的Json处理方法：

树模型(Tree Model)：是最灵活的处理方式
流式API(Streaming API)：是效率最高的处理方式(开销低、读写速度快，但程序编写复杂度高)
数据绑定(Data Binding)：是最常用的处理方式

下面从结合具体的实战来看一下，首先在pom.xml文件中添加以下三个依赖：

<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->    <dependency>      <groupId>com.fasterxml.jackson.core</groupId>      <artifactId>jackson-databind</artifactId>      <version>2.9.10</version>    </dependency>    <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-annotations -->    <dependency>      <groupId>com.fasterxml.jackson.core</groupId>      <artifactId>jackson-annotations</artifactId>      <version>2.9.10</version>    </dependency>
    <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-core -->    <dependency>      <groupId>com.fasterxml.jackson.core</groupId>      <artifactId>jackson-core</artifactId>      <version>2.9.10</version>    </dependency>

树模型(Tree Model)

tree model生成json

package com.jacksonTest;
import com.fasterxml.jackson.core.JsonFactory;import com.fasterxml.jackson.core.JsonGenerator;import com.fasterxml.jackson.databind.ObjectMapper;import com.fasterxml.jackson.databind.SerializationFeature;import com.fasterxml.jackson.databind.node.ArrayNode;import com.fasterxml.jackson.databind.node.JsonNodeFactory;import com.fasterxml.jackson.databind.node.ObjectNode;
import java.io.File;import java.io.FileWriter;
public class SerializationExampleTreeModel {    public static void main(String[] args) throws Exception {        //创建一个节点工厂,为我们提供所有节点        JsonNodeFactory factory = new JsonNodeFactory(false);        //创建一个json factory来写tree    modle为json        JsonFactory jsonFactory = new JsonFactory();        //创建一个json生成器        JsonGenerator generator = jsonFactory.createGenerator(new FileWriter(new File("country2.json")));        //注意，默认情况下对象映射器不会指定根节点，下面设根节点为country        ObjectMapper mapper = new ObjectMapper();        ObjectNode country = factory.objectNode();
        country.put("country_id", "China");        country.put("birthDate", "1949-10-01");
        //在Java中，List和Array转化为json后对应的格式符号都是"obj:[]"        ArrayNode nation = factory.arrayNode();        nation.add("Han").add("Meng").add("Hui").add("WeiWuEr").add("Zang");        country.set("nation", nation);
        ArrayNode lakes = factory.arrayNode();        lakes.add("QingHai Lake").add("Poyang Lake").add("Dongting Lake").add("Taihu Lake");        country.set("lakes", lakes);
        ArrayNode provinces = factory.arrayNode();        ObjectNode province = factory.objectNode();        ObjectNode province2 = factory.objectNode();        province.put("name","Shanxi");        province.put("population", 37751200);        province2.put("name","ZheJiang");        province2.put("population", 55080000);        provinces.add(province).add(province2);        country.set("provinces", provinces);
        ObjectNode traffic = factory.objectNode();        traffic.put("HighWay(KM)", 4240000);        traffic.put("Train(KM)", 112000);        country.set("traffic", traffic);
        mapper.configure(SerializationFeature.INDENT_OUTPUT, true);        mapper.writeTree(generator, country);    }}

程序运行生成country2.json：

【安全研究】Jackson 学习笔记

{"country_id":"China","birthDate":"1949-10-01","nation":["Han","Meng","Hui","WeiWuEr","Zang"],"lakes":["QingHai Lake","Poyang Lake","Dongting Lake","Taihu Lake"],"provinces":[{"name":"Shanxi","population":37751200},{"name":"ZheJiang","population":55080000}],"traffic":{"HighWay(KM)":4240000,"Train(KM)":112000}}

json反序列化为tree mode1

package com.jacksonTest;
import com.fasterxml.jackson.databind.JsonNode;import com.fasterxml.jackson.databind.ObjectMapper;import java.io.File;import java.util.Iterator;
public class DeserializationExampleTreeModel1 {    public static void main(String[] args) throws Exception {        ObjectMapper mapper = new ObjectMapper();        // Jackson提供一个树节点被称为"JsonNode",ObjectMapper提供方法来读json作为树的JsonNode根节点        JsonNode node = mapper.readTree(new File("country2.json"));        // 看看根节点的类型        System.out.println("node JsonNodeType:"+node.getNodeType());        // 是不是一个容器        System.out.println("node is container Node ? "+node.isContainerNode());        // 得到所有node节点的子节点名称        System.out.println("---------得到所有node节点的子节点名称-------------------------");        Iterator<String> fieldNames = node.fieldNames();        while (fieldNames.hasNext()) {            String fieldName = fieldNames.next();            System.out.print(fieldName+" ");        }        System.out.println("n-----------------------------------------------------");        // as.Text的作用是有值返回值，无值返回空字符串        JsonNode country_id = node.get("country_id");        System.out.println("country_id:"+country_id.asText() + " JsonNodeType:"+country_id.getNodeType());
        JsonNode birthDate = node.get("birthDate");        System.out.println("birthDate:"+birthDate.asText()+" JsonNodeType:"+birthDate.getNodeType());
        JsonNode nation = node.get("nation");        System.out.println("nation:"+ nation+ " JsonNodeType:"+nation.getNodeType());
        JsonNode lakes = node.get("lakes");        System.out.println("lakes:"+lakes+" JsonNodeType:"+lakes.getNodeType());
        JsonNode provinces = node.get("provinces");        System.out.println("provinces JsonNodeType:"+provinces.getNodeType());
        boolean flag = true;        for (JsonNode provinceElements : provinces) {            //为了避免provinceElements多次打印，用flag控制，打印能体现provinceElements的JsonNodeType就可以了            if(flag){                System.out.println("provinceElements JsonNodeType:"+provinceElements.getNodeType());                System.out.println("provinceElements is container node? "+provinceElements.isContainerNode());                flag = false;            }            Iterator<String> provinceElementFields = provinceElements.fieldNames();            while (provinceElementFields.hasNext()) {                String fieldName = (String) provinceElementFields.next();                String province;                if ("population".equals(fieldName)) {                    province = fieldName + ":" + provinceElements.get(fieldName).asInt();                }else{                    province = fieldName + ":" + provinceElements.get(fieldName).asText();                }                System.out.println(province);            }        }    }}

程序运行后打印结果如下：

【安全研究】Jackson 学习笔记

json反序列化为tree mode2

再来看一下DeserializationExampleTreeModel2.java，本例中使用JsonNode.path的方法，path方法类似于DeserializationExampleTreeModel1.java中使用的get方法，但当node不存在时get方法返回null，而path返回MISSING类型的JsonNode

package com.jacksonTest;
import com.fasterxml.jackson.core.JsonProcessingException;import com.fasterxml.jackson.databind.JsonNode;import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.File;import java.io.IOException;import java.util.Iterator;
public class DeserializationExampleTreeModle2 {    public static void main(String[] args) throws JsonProcessingException, IOException {        ObjectMapper mapper = new ObjectMapper();        JsonNode node = mapper.readTree(new File("country2.json"));        //path方法获取JsonNode时，当对象不存在时，返回MISSING类型的JsonNode        JsonNode missingNode = node.path("test");        if(missingNode.isMissingNode()){            System.out.println("JsonNodeType : " + missingNode.getNodeType());        }
        System.out.println("country_id:"+node.path("country_id").asText());
        JsonNode provinces = node.path("provinces");        for (JsonNode provinceElements : provinces) {            Iterator<String> provincesFields = provinceElements.fieldNames();            while (provincesFields.hasNext()) {                String fieldName = (String) provincesFields.next();                String province;                if("name".equals(fieldName)){                    province = fieldName +":"+ provinceElements.path(fieldName).asText();                }else{                    province = fieldName +":"+ provinceElements.path(fieldName).asInt();                }                System.out.println(province);            }        }    }}

程序运行打印结果：

【安全研究】Jackson 学习笔记

流式API(Streaming API)

Stream生成json

package com.jacksonTest;
import com.fasterxml.jackson.core.JsonFactory;import com.fasterxml.jackson.core.JsonGenerator;
import java.io.File;import java.io.FileWriter;
public class StreamGeneratorJson {    public static void main(String[] args) throws Exception {        JsonFactory factory = new JsonFactory();        //从JsonFactory创建一个JsonGenerator生成器的实例        JsonGenerator generator = factory.createGenerator(new FileWriter(new File("country3.json")));
        generator.writeStartObject();        generator.writeFieldName("country_id");        generator.writeString("China");        generator.writeFieldName("provinces");        generator.writeStartArray();        generator.writeStartObject();        generator.writeStringField("name", "Shanxi");        generator.writeNumberField("population", 33750000);        generator.writeEndObject();        generator.writeEndArray();        generator.writeEndObject();        generator.close();    }}

程序运行后生成country3.json文件内容：

【安全研究】Jackson 学习笔记

stream解析json

现在我们用Streaming API的方式来解析上面的Json,并查找json中population的值:

package com.jacksonTest;
import com.fasterxml.jackson.core.JsonFactory;import com.fasterxml.jackson.core.JsonParseException;import com.fasterxml.jackson.core.JsonParser;import com.fasterxml.jackson.core.JsonToken;
import java.io.File;import java.io.IOException;
public class StreamParserJson {    public static void main(String[] args) throws JsonParseException, IOException {        JsonFactory factory = new JsonFactory();        // 从JsonFactory创建JsonParser解析器的实例        JsonParser parser = factory.createParser(new File("country3.json"));        while (!parser.isClosed()) {            // 得到一个token,第一次遍历时，token指向json文件中第一个符号"{"            JsonToken token = parser.nextToken();            if (token == null) {                break;            }            // 我们只查找 country3.json中的"population"字段的值，能体现解析的流程就可以了            // 当key是provinces时，我们进入provinces,查找population            if (JsonToken.FIELD_NAME.equals(token)&& "provinces".equals(parser.getCurrentName())) {                token = parser.nextToken();                if (!JsonToken.START_ARRAY.equals(token)) {                    break;                }                // 此时，token指向的应该是"{"                token = parser.nextToken();                if (!JsonToken.START_OBJECT.equals(token)) {                    break;                }                while (true) {                    token = parser.nextToken();                    if (token == null) {                        break;                    }                    if ( JsonToken.FIELD_NAME.equals(token)                            &&"population".equals(parser.getCurrentName())) {                        token = parser.nextToken();                        System.out.println(parser.getCurrentName() + " : "                                + parser.getIntValue());                    }                }            }        }    }}

程序运行后，在控制台打印结果如下：

【安全研究】Jackson 学习笔记

数据绑定(Data Binding)

数据绑定简介

数据绑定API用于JSON转换和使用属性访问或使用注解POJO(普通Java对象)，以下是它的两个类型：

简单数据绑定 - 转换JSON，从Java Maps, Lists, Strings, Numbers, Booleans和null对象
完整数据绑定 - 转换JSON到任何JAVA类型

ObjectMapper读/写JSON两种类型的数据绑定，数据绑定是最方便的方式是类似XML的JAXB解析器

简单数据绑定

简单的数据绑定是指JSON映射到Java核心数据类型，下表列出了JSON类型和Java类型之间的关系：

【安全研究】Jackson 学习笔记

具体代码示例：

package com.jacksonTest;
import com.fasterxml.jackson.core.JsonParseException;import com.fasterxml.jackson.databind.JsonMappingException;import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.File;import java.io.IOException;import java.util.HashMap;import java.util.Map;
public class JacksonTester {    public static void main(String args[]){        JacksonTester tester = new JacksonTester();        try {            ObjectMapper mapper = new ObjectMapper();
            Map<String,Object> studentDataMap = new HashMap<String,Object>();            int[] marks = {1,2,3};
            Student student = new Student();            student.setAge(10);            student.setName("Mahesh");            // JAVA Object            studentDataMap.put("student", student);            // JAVA String            studentDataMap.put("name", "Mahesh Kumar");            // JAVA Boolean            studentDataMap.put("verified", Boolean.FALSE);            // Array            studentDataMap.put("marks", marks);
            mapper.writeValue(new File("student.json"), studentDataMap);            //result student.json            //{            //   "student":{"name":"Mahesh","age":10},            //   "marks":[1,2,3],            //   "verified":false,            //   "name":"Mahesh Kumar"            //}            studentDataMap = mapper.readValue(new File("student.json"), Map.class);
            System.out.println(studentDataMap.get("student"));            System.out.println(studentDataMap.get("name"));            System.out.println(studentDataMap.get("verified"));            System.out.println(studentDataMap.get("marks"));        } catch (JsonParseException e) {            e.printStackTrace();        } catch (JsonMappingException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        }    }}
class Student {    private String name;    private int age;    public Student(){}    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 String toString(){        return "Student [ name: "+name+", age: "+ age+ " ]";    }}

运行结果如下所示：

【安全研究】Jackson 学习笔记

完全数据绑定

完全数据绑定是指JSON映射到任何Java对象，例如：

//Create an ObjectMapper instanceObjectMapper mapper = new ObjectMapper();  
//map JSON content to Student objectStudent student = mapper.readValue(new File("student.json"), Student.class);
//map Student object to JSON contentmapper.writeValue(new File("student.json"), student);

具体代码示例：

package com.jacksonTest;
import com.fasterxml.jackson.core.JsonGenerationException;import com.fasterxml.jackson.core.JsonParseException;import com.fasterxml.jackson.databind.JsonMappingException;import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.File;import java.io.IOException;
public class JacksonTester {    public static void main(String args[]){        JacksonTester tester = new JacksonTester();        try {            Student student = new Student();            student.setAge(10);            student.setName("Mahesh");            tester.writeJSON(student);
            Student student1 = tester.readJSON();            System.out.println(student1);
        } catch (JsonParseException e) {            e.printStackTrace();        } catch (JsonMappingException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        }    }
    private void writeJSON(Student student) throws JsonGenerationException, JsonMappingException, IOException{        ObjectMapper mapper = new ObjectMapper();        mapper.writeValue(new File("student.json"), student);    }
    private Student readJSON() throws JsonParseException, JsonMappingException, IOException{        ObjectMapper mapper = new ObjectMapper();        Student student = mapper.readValue(new File("student.json"), Student.class);        return student;    }}
class Student {    private String name;    private int age;    public Student(){}    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 String toString(){        return "Student [ name: "+name+", age: "+ age+ " ]";    }}

运行结果如下所示：

【安全研究】Jackson 学习笔记

java对象序列化为json

Province.java：

package com.jacksonTest;
public class Province {    public String name;    public int population;    public String[] city;}

Country.java：

package com.jacksonTest;
import java.util.*;
public class Country {    // 注意：被序列化的bean的private属性字段需要创建getter方法或者属性字段应该为public    private String country_id;    private Date birthDate;    private List<String> nation = new ArrayList<String>();    private String[] lakes;    private List<Province> provinces = new ArrayList<Province>();    private Map<String, Integer> traffic = new HashMap<String, Integer>();        public Country() {        // TODO Auto-generated constructor stub    }
    public Country(String countryId) {        this.country_id = countryId;    }
    public String getCountry_id() {        return country_id;    }
    public void setCountry_id(String country_id) {        this.country_id = country_id;    }
    public Date getBirthDate() {        return birthDate;    }
    public void setBirthDate(Date birthDate) {        this.birthDate = birthDate;    }
    public List<String> getNation() {        return nation;    }
    public void setNation(List<String> nation) {        this.nation = nation;    }
    public String[] getLakes() {        return lakes;    }
    public void setLakes(String[] lakes) {        this.lakes = lakes;    }
    public Integer get(String key) {        return traffic.get(key);    }
    public Map<String, Integer> getTraffic() {        return traffic;    }
    public void setTraffic(Map<String, Integer> traffic) {        this.traffic = traffic;    }
    public void addTraffic(String key, Integer value) {        traffic.put(key, value);    }
    public List<Province> getProvinces() {        return provinces;    }
    public void setProvinces(List<Province> provinces) {        this.provinces = provinces;    }
    @Override    public String toString() {        return "Country [country_id=" + country_id + ", birthDate=" + birthDate                + ", nation=" + nation + ", lakes=" + Arrays.toString(lakes)                + ", province=" + provinces + ", traffic=" + traffic + "]";    }}

JavaBeanSerializeToJson.java

package com.jacksonTest;
import com.fasterxml.jackson.annotation.JsonInclude;import com.fasterxml.jackson.databind.ObjectMapper;import com.fasterxml.jackson.databind.SerializationFeature;
import java.io.File;import java.text.SimpleDateFormat;import java.util.ArrayList;import java.util.List;
public class JavaBeanSerializeToJson {    public static void convert() throws Exception {        // 使用ObjectMapper来转化对象为Json        ObjectMapper mapper = new ObjectMapper();        // 添加功能，让时间格式更具有可读性        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");        mapper.setDateFormat(dateFormat);
        Country country = new Country("China");        country.setBirthDate(dateFormat.parse("1949-10-01"));        country.setLakes(new String[] { "Qinghai Lake", "Poyang Lake",                "Dongting Lake", "Taihu Lake"});
        List<String> nation = new ArrayList<String>();        nation.add("Han");        nation.add("Meng");        nation.add("Hui");        nation.add("WeiWuEr");        nation.add("Zang");        country.setNation(nation);
        Province province = new Province();        province.name = "Shanxi";        province.population = 37751200;                Province province2 = new Province();        province2.name = "ZheJiang";        province2.population = 55080000;                List<Province> provinces = new ArrayList<Province>();        provinces.add(province);        provinces.add(province2);        country.setProvinces(provinces);
        country.addTraffic("Train(KM)", 112000);        country.addTraffic("HighWay(KM)", 4240000);        // 为了使JSON视觉上的可读性，增加一行如下代码，注意，在生产中不需要这样，因为这样会增大Json的内容        mapper.configure(SerializationFeature.INDENT_OUTPUT, true);        // 配置mapper忽略空属性        mapper.setSerializationInclusion(JsonInclude.Include.NON_EMPTY);        // 默认情况，Jackson使用Java属性字段名称作为 Json的属性名称,也可以使用Jackson annotations(注解)改变Json属性名称        mapper.writeValue(new File("country.json"), country);    }
    public static void main(String[] args) throws Exception {        convert();    }}

程序运行后生成country.json：

【安全研究】Jackson 学习笔记

Json反序列化为java对象

package com.jacksonTest;
import com.fasterxml.jackson.databind.DeserializationFeature;import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.File;import java.text.SimpleDateFormat;import java.util.List;
public class JsonDeserializeToJava {    public static void main(String[] args) throws Exception {        //ObjectMapper类用序列化与反序列化映射器          ObjectMapper mapper = new ObjectMapper();        File json = new File("country.json");        //当反序列化json时，未知属性会引起的反序列化被打断，这里我们禁用未知属性打断反序列化功能，          //因为，例如json里有10个属性，而我们的bean中只定义了2个属性，其它8个属性将被忽略          mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
        //从json映射到java对象，得到country对象后就可以遍历查找,下面遍历部分内容，能说明问题就可以了          Country country = mapper.readValue(json, Country.class);        System.out.println("country_id:"+country.getCountry_id());        //设置时间格式，便于阅读          SimpleDateFormat dateformat = new SimpleDateFormat("yyyy-MM-dd");        String birthDate = dateformat.format(country.getBirthDate());        System.out.println("birthDate:"+birthDate);
        List<Province> provinces = country.getProvinces();        for (Province province : provinces) {            System.out.println("province:"+province.name + "n" + "population:"+province.population);        }    }}

程序运行结果：

【安全研究】Jackson 学习笔记

ObjectMapper使用特性

在默认情况下ObjectMapper在序列化时会将所有的字段逐一序列化，无论这些字段是否有值，或者为null，另外序列化依赖于getter方法，如果某个字段没有getter方法，那么该字段是不会被序列化的，由此可见在序列化时OjbectMapper是通过反射机制找到了对应的getter，然后将getter方法对应的字段序列化到Json中~

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【安全研究】Jackson 学习笔记

基本介绍

解析处理

类声明

嵌套类

构造函数

继承的方法

数据处理

Json处理方法分类

树模型(Tree Model)

tree model生成json

json反序列化为tree mode2

流式API(Streaming API)

Stream生成json

stream解析json

数据绑定(Data Binding)

数据绑定简介

简单数据绑定

完全数据绑定

java对象序列化为json

ObjectMapper使用特性

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