转：将JSON数据转换成JAVA的实体类

思路：首先将JSON格式的数据转换成JSONObject，然后将JSONObject转换成Java的实体类（其中类属性包括List等类型）

Java实体类：

SearchFilter 类：

public class SearchFilter {
    private String groupOp;
    
    private List<SearchRule> rules;

    public String getGroupOp() {
        return groupOp;
    }

    public void setGroupOp(String groupOp) {
        this.groupOp = groupOp;
    }

    public List<SearchRule> getRules() {
        return rules;
    }

    public void setRules(List<SearchRule> rules) {
        this.rules = rules;
    }
}

SearchRule 类：

public class SearchRule {
    private String field;
    private String op;
    private String data;
    public String getField() {
        return field;
    }
    public void setField(String field) {
        this.field = field;
    }
    public String getOp() {
        return op;
    }
    public void setOp(String op) {
        this.op = op;
    }
    public String getData() {
        return data;
    }
    public void setData(String data) {
        this.data = data;
    }
}

导入的package

 import com.fasterxml.jackson.databind.ObjectMapper;
 import net.sf.json.JSONArray;
 import net.sf.json.JSONObject;

解析JSON格式字符串的方法

public SearchFilter jsonToSearchFilter(String filters) {
        SearchFilter searchFilter = null;
        try {
            JSONObject jsonobject = JSONObject.fromObject(filters);//将json格式的字符串转换成JSONObject 对象
            JSONArray array = jsonobject.getJSONArray("rules");    //如果json格式的字符串里含有数组格式的属性，将其转换成JSONArray，以方便后面转换成对应的实体
            List<SearchRule> rules = new ArrayList<SearchRule>();
            for (int i = 0; i < array.size(); i++) {
                JSONObject object = (JSONObject) array.get(i);     //将array中的数据进行逐条转换
                SearchRule rule = (SearchRule) JSONObject.toBean(object, SearchRule.class);  //通过JSONObject.toBean()方法进行对象间的转换
                rules.add(rule);
            }
            String groupOp = jsonobject.getString("groupOp");  //简单的直接获取值
            searchFilter = new SearchFilter();                 //对SearchFilter对象进行组装
            searchFilter.setGroupOp(groupOp);
            searchFilter.setRules(rules);
        } catch (Exception e) {
            System.out.println("filters=" + filters.toString() + ".json转换成实体类出错");
            e.printStackTrace();
        }
        return searchFilter;
    }

这里只进行了SearchFilter类中list<SearchRule>rule属性的对象转换，因为它是一个SearchRule对象数组，需要单独拿出来进行json转换成对象，如果直接对filter进行 SearchFilter进行实体转换会报错。如果对象中不含有list,array，map等集合，可以像8-9行一样进行对象转换。

测试：

public static void main(String[] args) {
        UserMgmtController con = new UserMgmtController();
        String filters="{"groupOp": "OR","rules": [{"field": "realname","op": "eq","+
                       ""data": "1234"},{"field": "cityCode","op": "ne","data": "5678"}]}";
        SearchFilter searchFilter =con.jsonToSearchFilter(filters);
        System.out.println("gop="+searchFilter.getGroupOp()+" rules.size="+searchFilter.getRules().size());
    }
结果：gop=OR rules.size=2

将java对象转换成json格式：

//将Object 对象转换成 json
    public String objectToJson(Object obj) {
        ObjectMapper mapper = new ObjectMapper();
        // Convert object to JSON string
        String jsonStr = null;
        try {
            jsonStr = mapper.writeValueAsString(obj);
        } catch (IOException e) {
            log.error(obj + "entity 轉換成 json出錯", e);
            e.printStackTrace();
            System.out.println("entity 轉換成 json出錯");
        }
        return jsonStr;
    }

将Object 转换成json字符串时，默认使用用是的驼峰方式，如果不想使用驼峰则可以增加红色部分设置，带下划线的也可以原样输出

public String objectToJson(Object obj){
        ObjectMapper mapper = new ObjectMapper();
        String json =null;
        try {
            PropertyNamingStrategy.PascalCaseStrategy pp = new PropertyNamingStrategy.PascalCaseStrategy();            
            mapper.setPropertyNamingStrategy(pp);
            json = mapper.writeValueAsString(obj);
        } catch (JsonProcessingException e) {
            log.error("json对象转换失败",e);
            e.printStackTrace();
        }
        return json;
    }

结果：

"UpLoadDateTime":"2017-09-25 10:51:41",
"OrganizationId":"B3EA5A4D-7C60-4C21-AF09-494890467C34" ，
"Test_Code":""