jackson学习（一）：jsonStringToList(js

前言

Jackson 是一个 Java 用来处理 JSON 格式数据的类库，性能非常好。

参考项目：https://github.com/bigbeef/cppba-jackson
开源地址：https://github.com/bigbeef
个人博客：http://blog.cppba.com

我也一直在用jackson，但是在开发过程中也遇到过一些需要花较长时间攻克的难题，我想把这些难题一一记录下来，给还没有攻克这个难题的jackson你们提供参考，希望你少走弯路。

1.maven的pom.xml配置

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.cppba</groupId>
  <artifactId>cppba-jackson</artifactId>
  <version>1.0.0</version>
  <packaging>jar</packaging>

  <name>cppba-jackson</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
     <!--关键这里，加入jackson库-->
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-databind</artifactId>
      <version>2.8.0</version>
    </dependency>
  </dependencies>
</project>

2.编写测试代码

2.1 json字符串直接转成List<JsonArrayToList >,代码复杂度较高

package com.cppba.jackson;

import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

public class StringToObject {
    public static ObjectMapper objectMapper = new ObjectMapper();

    public static void main(String[] args) throws IOException {
        String jsonStr = "[{\"id\":\"1\",\"values\":[\"1\",\"2\"]},{\"id\":\"2\",\"values\":[\"11\",\"22\"]}]";
        JavaType javaType = getCollectionType(ArrayList.class, JsonArrayToList.class);
        List<JsonArrayToList> list = objectMapper.readValue(jsonStr, javaType);
        for (JsonArrayToList jatl : list) {
            System.out.println(jatl.toString());
        }
    }

    public static JavaType getCollectionType(Class<?> collectionClass, Class<?>... elementClasses) {
        return objectMapper.getTypeFactory().constructParametricType(collectionClass, elementClasses);
    }
}

class JsonArrayToList {
    @JsonProperty("id")
    private String id;

    @JsonProperty("values")
    private List<Integer> values;

    @Override
    public String toString() {
        return "JsonArrayToList{" +
                "id='" + id + '\'' +
                ", values=" + values +
                '}';
    }
}

2.2json字符串转成JsonArrayToList[]，代码实现比较简单

package com.cppba.jackson;

import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.IOException;
import java.util.List;

public class StringToObject {
    public static ObjectMapper objectMapper = new ObjectMapper();

    public static void main(String[] args) throws IOException {
        String jsonStr = "[{\"id\":\"1\",\"values\":[\"1\",\"2\"]},{\"id\":\"2\",\"values\":[\"11\",\"22\"]}]";
        JsonArrayToList[] jsonArrayToList = objectMapper.readValue(jsonStr, JsonArrayToList[].class);
        for (JsonArrayToList jatl : jsonArrayToList) {
            System.out.println(jatl.toString());
        }
    }
}

class JsonArrayToList {
    @JsonProperty("id")
    private String id;

    @JsonProperty("values")
    private List<Integer> values;

    @Override
    public String toString() {
        return "JsonArrayToList{" +
                "id='" + id + '\'' +
                ", values=" + values +
                '}';
    }
}

3.运行结果

无论你是2.1还是2.2的方法实现，运行结果都是一样，如下图：

https://github.com/bigbeef

4：推荐

其实在业务需求满足的情况下，个人还是推荐2.2的实现方式，代码简单，容易理解！