用到的类库为：Jackson 版本1.9.5， 最近在看Google guava,所以用上了，版本是12.0-rc1
废话不多说，定义两个Bean 先
这两个bean 是父子关系。
java代码
public class User { PRivate String name; private Date createDate; private Set<Article> articles = Sets.newHashSet(); public String getName() { return name; } public void setName(String name) { this.name = name; } public Date getCreateDate() { return createDate; } public void setCreateDate(Date createDate) { this.createDate = createDate; } public Set<Article> getArticles() { return articles; } public void setArticles(Set<Article> articles) { this.articles = articles; } } Java代码 public class Article { private String title; private User user; public String getTitle() { return title; } public void setTitle(String title) { this.title = title; } public User getUser() { return user; } public void setUser(User user) { this.user = user; } } 然后自己写的一个Jackson实用类
Java代码public class Jacksons { private ObjectMapper objectMapper; public static Jacksons me() { return new Jacksons(); } private Jacksons() { objectMapper = new ObjectMapper(); // 设置输入时忽略在JSON字符串中存在但Java对象实际没有的属性 objectMapper.disable(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES); objectMapper.configure(SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS, false); objectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd")); } public Jacksons filter(String filterName, String... properties) { FilterProvider filterProvider = new SimpleFilterProvider().addFilter(filterName, SimpleBeanPropertyFilter.serializeAllExcept(properties)); objectMapper.setFilters(filterProvider); return this; } public Jacksons addMixInAnnotations(Class<?> target, Class<?> mixinSource) { objectMapper.getSerializationConfig().addMixInAnnotations(target, mixinSource); objectMapper.getDeserializationConfig().addMixInAnnotations(target, mixinSource); return this; } public Jacksons setDateFormate(DateFormat dateFormat) { objectMapper.setDateFormat(dateFormat); return this; } public <T> T json2Obj(String json, Class<T> clazz) { try { return objectMapper.readValue(json, clazz); } catch (Exception e) { e.printStackTrace(); throw new RuntimeException("解析json错误"); } } public String readAsString(Object obj) { try { return objectMapper.writeValueAsString(obj); } catch (Exception e) { e.printStackTrace(); throw new RuntimeException("解析对象错误"); } } @SuppressWarnings("unchecked") public List<Map<String, Object>> json2List(String json) { try { return objectMapper.readValue(json, List.class); } catch (Exception e) { e.printStackTrace(); throw new RuntimeException("解析json错误"); } } } 最后是测试：
Java代码public class Test { public static void main(String args[]) { User user = new User(); user.setName("chris"); user.setCreateDate(new Date()); Article article = new Article(); article.setTitle("title"); article.setUser(user); Set<Article> articles = Sets.newHashSet(article); user.setArticles(articles); String userJson = Jacksons.me().readAsString(user); String articleJson = Jacksons.me().readAsString(article); System.out.println(userJson); System.out.println(articleJson); } } 1.父子关系引用
直接输出肯定是报循环错误，Jackson 提供了两个注解
@JsonManagedReference
public Set<Article> getArticles() {
return articles;
}
@JsonBackReference
public User getUser() {
return user;
}
打印结果为：{"name":"chris","createDate":"2012-04-18","articles":[{"title":"title"}]}， {"title":"title"}
2.@JsonIgnore注解
只说父子引用关系的。父子两边都加@JsonIgnore打印字符串为:
{"name":"chris","createDate":"2012-04-18"}，{"title":"title"}
单向User加该注解
@JsonIgnore
public Set<Article> getArticles() {
return articles;
}
打印结果为:
{"name":"chris","createDate":"2012-04-18"}
{"title":"title","user":{"name":"chris","createDate":"2012-04-18"}}
单向Article 加该注解
@JsonIgnore
public User getUser() {
return user;
}
打印结果:
{"name":"chris","createDate":"2012-04-18","articles":[{"title":"title"}]}
{"title":"title"}
3.@JsonIgnoreType（没用过）
4.@JsonIgnoreProperties
这个加在类级别上, 用法很简单@JsonIgnoreProperties({"property1", "property2"})
动态过滤属性，这个比较麻烦。
有两种方法。
1.使用@JsonFilter注解
使用方法为先给ObjectMapper添加一个filter，然后还要在需要过滤的类上加@JsonFilter("filterName")注解。
比如说要过滤User 上的name属性，先
Jacksons.me().filter("myFilter", "name").readAsString(user)，具体看Jacksons代码。并在User类上加@JsonFilter("myFilter")。
有点不爽的是如果用另外一个没有添加该filter的ObjectMapper解析的话会报错。
如果这个User类已经添加了@JsonFilter("myFilter")注解，但在另外一个地方又要解析它并不想过滤name 属性，那只能是
Jacksons.me().filter("myFilter", "")，然后在读出来。
2.添加混入注解(暂时这么翻译)
定义一个接口或类先, 在该类上添加@JsonIgnoreProperties("name"), 然后在ObjectMapper的配置项上添加混入注解
输出为:
String mixInUser = Jacksons.me().addMixInAnnotations(User.class, MixInUser.class).readAsString(user);
System.out.println(mixInUser);
新闻热点
疑难解答
