Jackson的使用

最新推荐文章于 2025-09-10 07:53:06 发布

原创最新推荐文章于 2025-09-10 07:53:06 发布 · 514 阅读

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#java #基础

Jackson可以轻松的将Java对象转换成json对象和xml文档，同样也可以将json、xml转换成Java对象。

一、一个简单的例子

将文件中的json数据转换成java对象。修改后再转换成json对象写入文件

1-1、文件json数据如下：

{
  "name" : { "first" : "Joe", "last" : "Sixpack" },
  "gender" : "MALE",
  "verified" : false,
  "userImage" : "Rm9vYmFyIQ=="
}

1-2、java对象

public class User {

    private Name name;

    private Gender gender;

    private boolean verified;

    private byte[] userImage;

    public enum Gender{
        MALE,FEMALE
    };

    class Name {
        private String first;
        private String last;

        public Name(){

        }

        public String getFirst() {
            return first;
        }

        public void setFirst(String first) {
            this.first = first;
        }

        public String getLast() {
            return last;
        }

        public void setLast(String last) {
            this.last = last;
        }
    }

    public Name getName() {
        return name;
    }

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

    public Gender getGender() {
        return gender;
    }

    public void setGender(Gender gender) {
        this.gender = gender;
    }

    public boolean isVerified() {
        return verified;
    }

    public void setVerified(boolean verified) {
        this.verified = verified;
    }

    public byte[] getUserImage() {
        return userImage;
    }

    public void setUserImage(byte[] userImage) {
        this.userImage = userImage;
    }

    @Override
    public String toString() {
        return "User{" +
                "name=" + name +
                ", gender=" + gender +
                ", verified=" + verified +
                ", userImage=" + Arrays.toString(userImage) +
                '}';
    }
}

1-3、使用jackson进行json对象转换

public class JacksonSimpleDemo {

    public static void main(String[] args) {
        String userFilePath = JacksonSimpleDemo.class.getResource("/").getPath()+"user.json";
        ObjectMapper mapper = new ObjectMapper();
        try {
            //将文件中的json数据转换成User对象
            User user = mapper.readValue(new File(userFilePath),User.class);
            System.out.println(user.toString());
            //将User对象修改后转成json数据并写入数据
            String changedFilePath = JacksonSimpleDemo.class.getResource("/").getPath()+"changed_user.json";
            user.setGender(User.Gender.FEMALE);
            mapper.writeValue(new File(changedFilePath),user);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

1-4、jsckson的maven坐标

<dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.5.3</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>
            <version>2.5.3</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-annotations</artifactId>
            <version>2.5.3</version>
        </dependency>

代码下载地址：http://download.youkuaiyun.com/detail/jasonware/8676999

二、使用Map、ArrayList等对象进行转换

2-1、Jackson默认类型转换：

JSON Type	Java Type
`object`	`LinkedHashMap<String,Object>`
`array`	`ArrayList<Object>`
`string`	`String`
`number (no fraction)`	`Integer`, `Long` or `BigInteger` (smallest applicable)
`number (fraction)`	`Double` (configurable to use `BigDecimal`)
`true\|false`	`Boolean`
`null`	`null`

下面，我们讲第“一”中的例子使用Map对象进行转换

<pre style="background-color:#ffffff;color:#000000;font-family:'Menlo';font-size:12.0pt;"><span style="color:#808080;font-style:italic;">//范型的使用方式
</span>String userFilePath_4_FMap = JacksonSimpleDemo.<span style="color:#000080;font-weight:bold;">class</span>.getResource(<span style="color:#008000;font-weight:bold;">"/"</span>).getPath()+<span style="color:#008000;font-weight:bold;">"user_4_FMap.json"</span>;
Map<String,User> userFMap = mapper.readValue(<span style="color:#000080;font-weight:bold;">new </span>File(userFilePath_4_FMap), <span style="color:#000080;font-weight:bold;">new </span>TypeReference<Map<String,User>>(){
});
System.<span style="color:#660e7a;font-weight:bold;font-style:italic;">out</span>.println(<span style="color:#008000;font-weight:bold;">"joe's lastName :"</span>+userFMap.get(<span style="color:#008000;font-weight:bold;">"joe"</span>).getName().getLast());

public class jacksonMapDemo { public static void main(String[] args) { String userFilePath = JacksonSimpleDemo.class.getResource("/").getPath()+"user.json"; ObjectMapper mapper = new ObjectMapper(); try { //读取json数据到Map对象 Map<String,Object> userMap = mapper.readValue(new File(userFilePath),Map.class); System.out.println(userMap); //写Map对象到json数据 Map<String,String> nameStruct = new HashMap<String,String>(); nameStruct.put("first", "Joe"); nameStruct.put("last", "may"); userMap.put("name", nameStruct); userMap.put("gender", "MALE"); userMap.put("verified", Boolean.FALSE); userMap.put("userImage", "Rm9vYmFyIQ=="); String changedFilePath = JacksonSimpleDemo.class.getResource("/").getPath()+"changed_user_4_map.json"; mapper.writeValue(new File(changedFilePath), userMap); } catch (IOException e) { e.printStackTrace(); } }}

我们可以看到控制台输出：

{name={first=Joe, last=Sixpack}, gender=MALE, verified=false, userImage=Rm9vYmFyIQ==}

以及生成的新文件内容

{"name":{"last":"may","first":"Joe"},"gender":"MALE","verified":false,"userImage":"Rm9vYmFyIQ=="}

2-2、上面例子我们使用了默认的Map<String,Object>类型，如果使用范型如Map<String,User>要怎么处理呢？java的擦除机制不允许使用Map<String,User>.class

jackson为范型提供了解决方案：

  Map<String,User> result = mapper.readValue(src, <span style="color:#FF0000;">new TypeReference<Map<String,User>>() { }</span>);

如：

json对象为：

{
  "joe":{
    "name" : { "first" : "Joe", "last" : "Sixpack" },
    "gender" : "MALE",
    "verified" : false,
    "userImage" : "Rm9vYmFyIQ=="
  }
}

代码为：

//范型的使用方式
            String userFilePath_4_FMap = JacksonSimpleDemo.class.getResource("/").getPath()+"user_4_FMap.json";
            Map<String,User> userFMap = mapper.readValue(new File(userFilePath_4_FMap), <span style="color:#FF6666;">new TypeReference<Map<String,User>>(){
            }</span>);
            System.out.println("joe's lastName :"+userFMap.get("joe").getName().getLast());

输出为：

joe's lastName :Sixpack

三、使用XML形式解析json。（json数据看起来就是一棵树结构）

public class JacksonXmlDemo {

    public static void main(String[] args) {
        String userFilePath = JacksonSimpleDemo.class.getResource("/").getPath()+"user.json";
        ObjectMapper mapper = new ObjectMapper();
        try {
            JsonNode rootNode = mapper.readTree(new File(userFilePath));
            JsonNode nameNode = rootNode.get("name");
            String   firstName = nameNode.get("first").asText();
            System.out.println("firstName is : "+firstName);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

输出结果为：