Jackson解析

public class JsonUtil {

    private final static ObjectMapper objectMapper = new ObjectMapper();

    private JsonUtil() {

    }

    public static ObjectMapper getInstance() {

        return objectMapper;
    }
    /**只能轉一級泛型如T<A,B...>*/
    public static <T> T toCollection(String jsonStr, Class<?> parametrized, Class<?>... parameterClasses) throws IOException {
        JavaType javaType = objectMapper.getTypeFactory().constructParametricType(parametrized,parameterClasses);
        return objectMapper.readValue(jsonStr, javaType);
    }

    /**
     * javaBean,list,array convert to json string
     */
    public static String obj2json(Object obj) throws Exception {
        return objectMapper.writeValueAsString(obj);
    }

    /**
     * json string convert to javaBean
     */
    public static <T> T json2pojo(String jsonStr, Class<T> clazz)
            throws Exception {
        return objectMapper.readValue(jsonStr, clazz);
    }

    /**
     * json string convert to map
     */
    public static <T> Map<String, Object> json2map(String jsonStr)
            throws Exception {
        return objectMapper.readValue(jsonStr, Map.class);
    }

    /**
     * json string convert to map with javaBean
     */
    public static <T> Map<String, T> json2map(String jsonStr, Class<T> clazz)
            throws Exception {
        Map<String, Map<String, Object>> map = objectMapper.readValue(jsonStr,
                new TypeReference<Map<String, T>>() {
                });
        Map<String, T> result = new HashMap<String, T>();
        for (Map.Entry<String, Map<String, Object>> entry : map.entrySet()) {
            result.put(entry.getKey(), map2pojo(entry.getValue(), clazz));
        }
        return result;
    }

    /**
     * json array string convert to list with javaBean
     */
    public static <T> List<T> json2list(String jsonArrayStr, Class<T> clazz)
            throws Exception {
        List<Map<String, Object>> list = objectMapper.readValue(jsonArrayStr,
                new TypeReference<List<T>>() {
                });
        List<T> result = new ArrayList<T>();
        for (Map<String, Object> map : list) {
            result.add(map2pojo(map, clazz));
        }
        return result;
    }
/**
 * json string 轉複雜多級的泛型類能夠用這個方法
 */
public static <T> T json2TypeReferenceObj(String jsonStr, Class<T> clazz)
        throws IOException {
    TypeReference ref = new TypeReference<T>(){};
    return objectMapper.readValue(jsonStr, ref);
}

    /**
     * map convert to javaBean
     */
    public static <T> T map2pojo(Map map, Class<T> clazz) {
        return objectMapper.convertValue(map, clazz);
    }

    public static <T> T readFromStream(InputStream inputStream, Class<?> parametrized, Class<?>... parameterClasses) throws IOException {
        JavaType javaType = objectMapper.getTypeFactory().constructParametricType(parametrized,parameterClasses);
        return objectMapper.readValue(inputStream,javaType);
    }
}

注意寫類的getter setter時候的問題：

jackson默認的字段屬性發現規則以下：全部被public修飾的字段->全部被public修飾的getter->全部被public修飾的setter

若是屬性是private 就讀不到了

Android Studio自動生成的getter setter會出問題的一個點是boolean類型，若是我把變量名定爲isXXX，自動生成的getter setter方法名是沒有get set字眼的，jackson就不能識別了，解決辦法就是本身手動把isXX變量的getter setter方法補全get set字眼。

對於json string字段多，java 對象的變量少的狀況，能夠有兩種處理方式，

1.統一處理，配置不要報錯：

ObjectMapper objectMapper = new ObjectMapper();
            objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES,false);

2.單獨每一個class處理:

@JsonIgnoreProperties(ignoreUnknown = true)
public class Foo{
}