JSONObject转换分析

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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<String, String> 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<String, Object> map = (Map<String, Object>) JSONObject.toBean(jsonObject, HashMap.class);
System.out.println(map.get("ts").toString());// Map<String, String> map = (Map<String, String>) 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