在工作中实际使用到Java处理JSON的情况，且有很大部分都使用的是开源工具Jackson实现的。

一.入门

Jackson中有个ObjectMapper类很是实用，用于Java对象与JSON的互换。

1.Java对象转换为JSON

Student st=new Student(); //Java Object

ObjectMapper mapper = new ObjectMapper();

java.text.DateFormat myFormat = new java.text.SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

mapper.getSerializationConfig().setDateFormat(myFormat);

try {

    //返回字符串

    String res = mapper.writeValueAsString(st);

    System.out.println(res);
//输出格式化后的字符串(有性能损耗)

res = mapper.defaultPrettyPrintingWriter().writeValueAsString(st);

System.out.println(res);

mapper.writeValue(new File("D:\\st.json"), st); //指定文件写入

//设置序列化配置(全局),设置序列化时不输出空值.

mapper.getSerializationConfig().setSerializationInclusion(Inclusion.NON_NULL);

res = mapper.writeValueAsString(st);

System.out.println(res);


} catch (Exception e) {


e.printStackTrace();


}

2.JSON反序列化为Java对象

String json = "{\"error\":0,\"data\":{\"name\":\"ABC\",\"age\":20,\"phone\":{\"home\":\"abc\",\"mobile\":\"def\"},\"friends\":[{\"name\":\"DEF\",\"phone\":{\"home\":\"hij\",\"mobile\":\"klm\"}},{\"name\":\"GHI\",\"phone\":{\"home\":\"nop\",\"mobile\":\"qrs\"}}]},\"other\":{\"nickname\":[]}}";

ObjectMapper mapper = new ObjectMapper();

//解析器支持解析单引号

mapper.configure(Feature.ALLOW_SINGLE_QUOTES, true);

//解析器支持解析结束符

mapper.configure(Feature.ALLOW_UNQUOTED_CONTROL_CHARS, true);

try {

    //转换为HashMap对象

    HashMap jsonMap = mapper.readValue(json, HashMap.class);

    Map<String, Map<String, Object>> maps = objectMapper.readValue(json, Map.class);

    System.out.println(maps.get("error"));//0

    System.out.println((Object) (maps.get("data").get("phone")));//{home=abc, mobile=def}

} catch (Exception e) {

    e.printStackTrace();

}

二.Jackson支持三种使用方式

1.Data Binding：最方便使用

(1)Full Data Binding

/*

 * Full Data Binding

 */

public static void fullDataBinding() {
ObjectMapper mapper = new ObjectMapper();

try {

    Model model = mapper.readValue(MODEL_BINDING, Model.class);

    //readValue到一个实体类中.

    System.out.println(model.getName()); //name1

    System.out.println(model.getType()); //1

} catch (Exception e) {

    e.printStackTrace();

}


}
private static class Model {


private String name;


private int type;
public String getName() {

    return name;

}

public void setName(String name) {

    this.name = name;

}

public int getType() {

    return type;

}

public void setType(int type) {

    this.type = type;

}


}

(2)Raw Data Binding

/*

 * Raw Data Binding

 */

public static void rawDataBinding() {

    ObjectMapper mapper = new ObjectMapper();

    try {

        HashMap map = mapper.readValue(MODEL_BINDING, HashMap.class);//readValue到一个原始数据类型.

        System.out.println(map.get("name")); //name1

        System.out.println(map.get("type")); //1

    } catch (Exception e) {

        e.printStackTrace();

    }

}

(3)generic Data Binding

/*

 * generic Data Binding

 */

public static void genericDataBinding() {
ObjectMapper mapper = new ObjectMapper();

try {

    HashMap<String, Model> modelMap = mapper.readValue(GENERIC_BINDING,

            new TypeReference<HashMap<String, Model>>() {

            });//readValue到一个范型数据中.

    Model model = modelMap.get("key2");

    System.out.println(model.getName()); //name3

    System.out.println(model.getType()); //3

} catch (Exception e) {

    e.printStackTrace();

}


}

2.Tree Model：最灵活

/*

 * Tree Model：最灵活

 */

public static void treeModelBinding() {

    ObjectMapper mapper = new ObjectMapper();

    try {

        JsonNode rootNode = mapper.readTree(TREE_MODEL_BINDING);

        //path与get作用相同,但是当找不到该节点的时候,返回missing node而不是Null.

        String treekey2value = rootNode.path("treekey2").getTextValue();//

        System.out.println("treekey2value:" + treekey2value);

        JsonNode childrenNode = rootNode.path("children");

        String childkey1Value = childrenNode.get(0).path("childkey1").getTextValue();

        System.out.println("childkey1Value:" + childkey1Value);
    //创建根节点

    ObjectNode root = mapper.createObjectNode();

    //创建子节点1

    ObjectNode node1 = mapper.createObjectNode();

    node1.put("nodekey1", 1);

    node1.put("nodekey2", 2);

    //绑定子节点1

    root.put("child", node1);

    //数组节点

    ArrayNode arrayNode = mapper.createArrayNode();

    arrayNode.add(node1);

    arrayNode.add(1);

    //绑定数组节点

    root.put("arraynode", arrayNode);

    //JSON读到树节点

    JsonNode valueToTreeNode = mapper.valueToTree(TREE_MODEL_BINDING);

    //绑定JSON节点

    root.put("valuetotreenode", valueToTreeNode);

    //JSON绑定到JSON节点对象

    JsonNode bindJsonNode = mapper.readValue(GENERIC_BINDING, JsonNode.class);//绑定JSON到JSON节点对象.

    //绑定JSON节点

    root.put("bindJsonNode", bindJsonNode);

    System.out.println(mapper.writeValueAsString(root));

} catch (Exception e) {

    e.printStackTrace();

}


}

3.Streaming API。最佳性能

见官方文档例子。

进一步学习资料:

1.http://wiki.fasterxml.com/JacksonInFiveMinutes Jackson官方教程示例

2.http://wiki.fasterxml.com/JacksonJavaDocs Jackson在线API文档

3.http://hjg1988.iteye.com/blog/561368 JSON工具性能比较:json-lib和jackson进行Java对象到json字符串序列化。

文章来源：http://shensy.iteye.com/blog/1717776