net.sf.json.JSONObject采用反射的方式，对POJO进行转换。JSONObject类实现了JSON、Map和Comparable接口，如下：

class JSONObject extends AbstractJSON implements JSON, Map, Comparable

以Person类为例分析源码：

public class Person {    private String name;    private int age;    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }}

 

 

fromObject(Object object)方法：

代码实现主要在JSONObject defaultBeanProcessing(Object bean, JsonConfig jsonConfig)方法中，如下：

private static JSONObject defaultBeanProcessing(Object bean, JsonConfig jsonConfig) {      Class beanClass = bean.getClass(); //获取类对象 class net.sf.json.mytest.Person      PropertyNameProcessor propertyNameProcessor = jsonConfig.findJsonPropertyNameProcessor( beanClass );            Collection exclusions = jsonConfig.getMergedExcludes( beanClass );//需要排除的类信息，[metaClass, declaringClass, class]      JSONObject jsonObject = new JSONObject();      try{         PropertyDescriptor[] pds = PropertyUtils.getPropertyDescriptors( bean );//获取POJO类的描述信息，包括属性、属性对应的读写操作， //[java.beans.PropertyDescriptor[name=age; propertyType=int; readMethod=public int net.sf.json.mytest.Person.getAge(); writeMethod=public void net.sf.json.mytest.Person.setAge(int)], //java.beans.PropertyDescriptor[name=class; propertyType=class java.lang.Class; readMethod=public final native java.lang.Class java.lang.Object.getClass()], //java.beans.PropertyDescriptor[name=name; propertyType=class java.lang.String; readMethod=public java.lang.String net.sf.json.mytest.Person.getName(); writeMethod=public void net.sf.json.mytest.Person.setName(java.lang.String)]]         PropertyFilter jsonPropertyFilter = jsonConfig.getJsonPropertyFilter();         //循环对所有属性进行处理         for( int i = 0; i < pds.length; i++ ){            boolean bypass = false;            //获取属性名            String key = pds[i].getName();            if( exclusions.contains( key ) ){               continue;            }            if( jsonConfig.isIgnoreTransientFields() && isTransientField( key, beanClass ) ){               continue;            }            Class type = pds[i].getPropertyType();            try { pds[i].getReadMethod(); }            catch( Exception e ) {               // bug 2565295               String warning = "Property '" + key + "' of "+ beanClass+" has no read method. SKIPPED";               fireWarnEvent( warning, jsonConfig );               log.info( warning );               continue;            }            if( pds[i].getReadMethod() != null ){               Object value = PropertyUtils.getProperty( bean, key );               if( jsonPropertyFilter != null && jsonPropertyFilter.apply( bean, key, value ) ){                  continue;               }               JsonValueProcessor jsonValueProcessor = jsonConfig.findJsonValueProcessor(                     beanClass, type, key );               if( jsonValueProcessor != null ){                  value = jsonValueProcessor.processObjectValue( key, value, jsonConfig );                  bypass = true;                  if( !JsonVerifier.isValidJsonValue( value ) ){                     throw new JSONException( "Value is not a valid JSON value. " + value );                  }               }               if( propertyNameProcessor != null ){                  key = propertyNameProcessor.processPropertyName( beanClass, key );               }               //设置属性值               setValue( jsonObject, key, value, type, jsonConfig, bypass );            }else{               String warning = "Property '" + key + "' of "+ beanClass+" has no read method. SKIPPED";               fireWarnEvent( warning, jsonConfig );               log.info( warning );            }         }        .......      }catch( JSONException jsone ){         removeInstance( bean );         fireErrorEvent( jsone, jsonConfig );         throw jsone;      }catch( Exception e ){         removeInstance( bean );         JSONException jsone = new JSONException( e );         fireErrorEvent( jsone, jsonConfig );         throw jsone;      }      return jsonObject;   }

 

toBean(JSONObject object, Class clazz)方法

由JSONObject对象转为对应类实例，关键代码在Object toBean( JSONObject jsonObject, JsonConfig jsonConfig )中，如下：

 public static Object toBean( JSONObject jsonObject, JsonConfig jsonConfig ) {

if( jsonObject == null || jsonObject.isNullObject() ){         return null;      }      Class beanClass = jsonConfig.getRootClass();//类对象      Map classMap = jsonConfig.getClassMap();      if( beanClass == null ){         return toBean( jsonObject );      }      if( classMap == null ){         classMap = Collections.EMPTY_MAP;      }      Object bean = null;      try{         if( beanClass.isInterface() ){            if( !Map.class.isAssignableFrom( beanClass ) ){               throw new JSONException( "beanClass is an interface. " + beanClass );            }else{               bean = new HashMap();            }         }else{            bean = jsonConfig.getNewBeanInstanceStrategy() //实例化                  .newInstance( beanClass, jsonObject );         }      }catch( JSONException jsone ){         throw jsone;      }catch( Exception e ){         throw new JSONException( e );      }      Map props = JSONUtils.getProperties( jsonObject );//属性及属性类型  {name=class java.lang.String, age=class java.lang.Integer}      PropertyFilter javaPropertyFilter = jsonConfig.getJavaPropertyFilter();      for( Iterator entries = jsonObject.names( jsonConfig )            .iterator(); entries.hasNext(); ){         String name = (String) entries.next();//属性名         Class type = (Class) props.get( name );//属性类型         Object value = jsonObject.get( name );//属性值，如果属性值为null,返回的值为JSONNull对象         if( javaPropertyFilter != null && javaPropertyFilter.apply( bean, name, value ) ){            continue;         }         String key = Map.class.isAssignableFrom( beanClass )               && jsonConfig.isSkipJavaIdentifierTransformationInMapKeys() ? name               : JSONUtils.convertToJavaIdentifier( name, jsonConfig );         PropertyNameProcessor propertyNameProcessor = jsonConfig.findJavaPropertyNameProcessor( beanClass );         if( propertyNameProcessor != null ){            key = propertyNameProcessor.processPropertyName( beanClass, key );         }         //设置实例对象的属性（处理各种情况）         try{            if( Map.class.isAssignableFrom( beanClass ) ){
   //Map对象单独处理               // no type info available for conversion               if( JSONUtils.isNull( value ) ){                  setProperty( bean, key, value, jsonConfig );               }else if( value instanceof JSONArray ){                  setProperty( bean, key, convertPropertyValueToCollection( key, value, jsonConfig, name,                        classMap, List.class ), jsonConfig );               }else if( String.class.isAssignableFrom( type ) || JSONUtils.isBoolean( type )                     || JSONUtils.isNumber( type ) || JSONUtils.isString( type )                     || JSONFunction.class.isAssignableFrom( type ) ){                  if( jsonConfig.isHandleJettisonEmptyElement() && "".equals( value ) ){                     setProperty( bean, key, null, jsonConfig );                  }else{                     setProperty( bean, key, value, jsonConfig );                  }               }else{                  Class targetClass = resolveClass(classMap, key, name, type);                  JsonConfig jsc = jsonConfig.copy();                  jsc.setRootClass( targetClass );                  jsc.setClassMap( classMap );                  if( targetClass != null ){                     setProperty( bean, key, toBean( (JSONObject) value, jsc ), jsonConfig );                  }else{                     setProperty( bean, key, toBean( (JSONObject) value ), jsonConfig );                  }               }            }else{               PropertyDescriptor pd = PropertyUtils.getPropertyDescriptor( bean, key );//获取属性描述 //java.beans.PropertyDescriptor[name=name; propertyType=class java.lang.String; readMethod=public java.lang.String net.sf.json.mytest.Person.getName(); writeMethod=public void net.sf.json.mytest.Person.setName(java.lang.String)]               if( pd != null && pd.getWriteMethod() == null ){                  log.info( "Property '" + key + "' of "+ bean.getClass()+" has no write method. SKIPPED." );                  continue;               }               if( pd != null ){                  Class targetType = pd.getPropertyType();                  if( !JSONUtils.isNull( value ) ){                     if( value instanceof JSONArray ){  //JSONArray值                        if( List.class.isAssignableFrom( pd.getPropertyType() ) ){                           setProperty( bean, key, convertPropertyValueToCollection( key, value,                                 jsonConfig, name, classMap, pd.getPropertyType() ), jsonConfig );                        }else if( Set.class.isAssignableFrom( pd.getPropertyType() ) ){                           setProperty( bean, key, convertPropertyValueToCollection( key, value,                                 jsonConfig, name, classMap, pd.getPropertyType() ), jsonConfig );                        }else{                           setProperty( bean, key, convertPropertyValueToArray( key, value,                                 targetType, jsonConfig, classMap ), jsonConfig );                        }                     }else if( String.class.isAssignableFrom( type ) || JSONUtils.isBoolean( type )  //基本类型                           || JSONUtils.isNumber( type ) || JSONUtils.isString( type )                           || JSONFunction.class.isAssignableFrom( type ) ){                        if( pd != null ){                           if( jsonConfig.isHandleJettisonEmptyElement() && "".equals( value ) ){                              setProperty( bean, key, null, jsonConfig );                           }else if( !targetType.isInstance( value ) ){                              setProperty( bean, key, morphPropertyValue( key, value, type,                                    targetType ), jsonConfig );                           }else{                              setProperty( bean, key, value, jsonConfig );//对String进行处理                           }                        }else if( beanClass == null || bean instanceof Map ){                           setProperty( bean, key, value, jsonConfig );                        }else{                           log.warn( "Tried to assign property " + key + ":" + type.getName()                                 + " to bean of class " + bean.getClass()                                       .getName() );                        }                     }else{                        if( jsonConfig.isHandleJettisonSingleElementArray() ){                           JSONArray array = new JSONArray().element( value, jsonConfig );                           Class newTargetClass = resolveClass(classMap, key, name, type);                           JsonConfig jsc = jsonConfig.copy();                           jsc.setRootClass( newTargetClass );                           jsc.setClassMap( classMap );                           if( targetType.isArray() ){                              setProperty( bean, key, JSONArray.toArray( array, jsc ), jsonConfig );                           }else if( JSONArray.class.isAssignableFrom( targetType ) ){                              setProperty( bean, key, array, jsonConfig );                           }else if( List.class.isAssignableFrom( targetType )                                 || Set.class.isAssignableFrom( targetType ) ){                              jsc.setCollectionType( targetType );                              setProperty( bean, key, JSONArray.toCollection( array, jsc ),                                    jsonConfig );                           }else{                              setProperty( bean, key, toBean( (JSONObject) value, jsc ), jsonConfig );                           }                        }else{                           if( targetType == Object.class || targetType.isInterface() ) {                              Class targetTypeCopy = targetType;                              targetType = findTargetClass( key, classMap );                              targetType = targetType == null ? findTargetClass( name, classMap )                                    : targetType;                              targetType = targetType == null && targetTypeCopy.isInterface() ? targetTypeCopy                                    : targetType;                           }                           JsonConfig jsc = jsonConfig.copy();                           jsc.setRootClass( targetType );                           jsc.setClassMap( classMap );                           setProperty( bean, key, toBean( (JSONObject) value, jsc ), jsonConfig );                        }                     }                  }else{                     if( type.isPrimitive() ){                        // assume assigned default value                        log.warn( "Tried to assign null value to " + key + ":" + type.getName() );                        setProperty( bean, key, JSONUtils.getMorpherRegistry()                              .morph( type, null ), jsonConfig );                     }else{                        setProperty( bean, key, null, jsonConfig );                     }                  }               }else{                  // pd is null                  if( !JSONUtils.isNull( value ) ){                     if( value instanceof JSONArray ){                        setProperty( bean, key, convertPropertyValueToCollection( key, value,                              jsonConfig, name, classMap, List.class ), jsonConfig );                     }else if( String.class.isAssignableFrom( type ) || JSONUtils.isBoolean( type )                           || JSONUtils.isNumber( type ) || JSONUtils.isString( type )                           || JSONFunction.class.isAssignableFrom( type ) ){                        if( beanClass == null || bean instanceof Map || jsonConfig.getPropertySetStrategy() != null ||                             !jsonConfig.isIgnorePublicFields() ){                           setProperty( bean, key, value, jsonConfig );                        }else{                           log.warn( "Tried to assign property " + key + ":" + type.getName()                                 + " to bean of class " + bean.getClass()                                       .getName() );                        }                     }else{                        if( jsonConfig.isHandleJettisonSingleElementArray() ){                           Class newTargetClass = resolveClass(classMap, key, name, type);                           JsonConfig jsc = jsonConfig.copy();                           jsc.setRootClass( newTargetClass );                           jsc.setClassMap( classMap );                           setProperty( bean, key, toBean( (JSONObject) value, jsc ), jsonConfig );                        }else{                           setProperty( bean, key, value, jsonConfig );                        }                     }                  }else{                     if( type.isPrimitive() ){                        // assume assigned default value                        log.warn( "Tried to assign null value to " + key + ":" + type.getName() );                        setProperty( bean, key, JSONUtils.getMorpherRegistry()                              .morph( type, null ), jsonConfig );                     }else{                        setProperty( bean, key, null, jsonConfig );                     }                  }               }            }         }catch( JSONException jsone ){            throw jsone;         }catch( Exception e ){            throw new JSONException( "Error while setting property=" + name + " type " + type, e );         }      }      return bean;   }

 另外，Map转JSONObject问题：

会将Map结构（{key=value}）转换为json格式（“key”:"value"）。

（1）java中的null，会转换为JSONNull对象，不能直接将该对象转为String。

（2）net.sf.json.JSONObject不支持Map中key为null的情况。

举例如下：

import java.util.HashMap;import java.util.Map;import net.sf.json.JSONNull;import net.sf.json.JSONObject;public class Test {    public static void main(String[] args) {        Map
     
       data1 = new HashMap<>();//        data1.put(null, "empty");  //报JSON keys cannot be null.        data1.put("ts", null);        System.out.println(data1.toString());        if(data1.get("ts")==null){            System.out.println("Map中的null");        }                JSONObject jsonObject = JSONObject.fromObject(data1);        System.out.println(jsonObject.toString());                if(JSONNull.getInstance().equals(jsonObject.get("ts"))){            System.out.println("Map中的null，转为net.sf.json.JSONObject后，变成net.sf.json.JSONNull");        }        Map
      
        map = (Map
       
        ) JSONObject.toBean(jsonObject, HashMap.class);        System.out.println(map.get("ts").toString());        //        Map
        
          map = (Map
         
          ) JSONObject.toBean(jsonObject, HashMap.class);//        System.out.println(map.get("ts").toString()); //java.lang.ClassCastException: net.sf.json.JSONNull cannot be cast to java.lang.String    }}
         
        
       
      
     

  结果：

{ts=null}Map中的null{
    "ts":null}Map中的null，转为net.sf.json.JSONObject后，变成net.sf.json.JSONNull