Json-lib 与 hibernate _lazy共同使用的问题

原文http://ericyou.iteye.com/blog/325246

hibernate使用CGLIB把POJO的domain对象动态代理，实现它的魔法，但是给JSON的序列化带来了麻烦，因为JSON无法对lazy的属性进行序列化。有以下的四个方法可以解决hibernate的序列化问题

domain类实现JSONString接口

建立JsonConfig实例，并配置属性排除列表

用属性过滤器

写一个自定义的JsonBeanProcessor

1.实现JSONString接口是侵入性最强的方法

public class Person implements JSONString {  
   private String name;  
   private String lastname;  
   private Address address;  
  
   // getters & setters  
  
   public String toJSONString() {  
      return "{name:'"+name+"',lastname:'"+lastname+"'}";  
   }  
}

2.第二种方法通过jsonconfig实例，对包含和需要排除的属性进行方便添加删除

public class Person {  
   private String name;  
   private String lastname;  
   private Address address;  
  
   // getters & setters  
}  
  
JsonConfig jsonConfig = new JsonConfig();  
jsonConfig.setExclusions( new String[]{ "address" } );  
Person bean = /* initialize */;  
JSON json = JSONSerializer.toJSON( bean, jsonConfig );

注意：这种方法不区分目标类，就是说如果有2个bean当中都存在“address”属性，那么采用这种方法，这两个bean中的address属性都将被排除

3.使用propertyFilter可以允许同时对需要排除的属性和类进行控制，这种控制还可以是双向的，也可以应用到json字符串到java对象

public class Person {  
   private String name;  
   private String lastname;  
   private Address address;  
  
   // getters & setters  
}  
  
JsonConfig jsonConfig = new JsonConfig();  
jsonConfig.setJsonPropertyFilter( new PropertyFilter(){  
   public boolean apply( Object source, String name, Object value ){  
      // return true to skip name  
      return source instanceof Person && name.equals("address");  
   }  
});  
Person bean = /* initialize */;  
JSON json = JSONSerializer.toJSON( bean, jsonConfig )

4.最后来看JsonBeanProcessor,这种方式和实现JsonString很类似，返回一个代表原来的domain类的合法JSONOBJECT

public class Person {  
   private String name;  
   private String lastname;  
   private Address address;  
  
   // getters & setters  
}  
  
JsonConfig jsonConfig = new JsonConfig();  
jsonConfig.registerJsonBeanProcessor( Person.class,  
   new JsonBeanProcessor(){  
      public JSONObject processBean( Object bean, JsonConfig jsonConfig ){  
         if( !(bean instanceof Person) ){  
            return new JSONObject(true);  
         }  
         Person person = (Person) bean;  
         return new JSONObject()  
            .element( "name", person.getName() )  
            .element( "lastname", person.getLastname() );  
      }  
});  
Person bean = /* initialize */;  
JSON json = JSONSerializer.toJSON( bean, jsonConfig );

AnditisherewithJsonBeanProcessorswhereweencounterthesecondgotcharelatedtoCGlib.AsyounoticedweregisteredtheprocessorusingPersonastargetclass,butHibernatereturnsaProxythatisnotexactlyaPersonbutasubclass(ifpossible)ofPerson.ThedefaultmatchingalgorithmusedbyJson-libwilltrytomatchtheexactclass(usingequals),meaningthatyourprocessorwillnotbecalledwhenyouexpectittobe,thisiswhyJsonBeanProcessorMatcherwasintroduced,nowyouarebeabletowritethefollowingcode

<textareaclass="java:nocontrols:nogutter"cols="80"rows="34"name="srccode">publicclassPerson{privateStringname;privateStringlastname;privateAddressaddress;//getters&setters}JsonConfigjsonConfig=newJsonConfig();jsonConfig.registerJsonBeanProcessor(Person.class,newJsonBeanProcessor(){publicJSONObjectprocessBean(Objectbean,JsonConfigjsonConfig){if(!(beaninstanceofPerson)){returnnewJSONObject(true);}Personperson=(Person)bean;returnnewJSONObject().element("name",person.getName()).element("lastname",person.getLastname());}});jsonConfig.registerJsonBeanProcessorMatcher(newJsonBeanProcessorMatcher(){publicObjectgetMatch(Classtarget,Set/*<Class>*/matches){for(Objectmatch:matches){if(((Class)match).isAssignableFrom(target)){returnmatch;}}returnnull;}});Personbean=/*initialize*/;JSONjson=JSONSerializer.toJSON(bean,jsonConfig);</textarea>

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