GSON 報錯HibernateProxy. Forgot to register a type adapter? 的解決辦法

使用Gson轉換hibernate對象遇到一個問題，當對象的Lazy加載的，就會出現上面的錯誤。處理方式摘抄自網上，留存一份以后自己看。

 

網上找到的解決辦法,首先自定義一個類繼承TypeAdapter:

package cn.xjy.finance.loanapply.utils ;

import java.io.IOException ;
import org.hibernate.Hibernate ;
import org.hibernate.proxy.HibernateProxy ;
import com.google.gson.Gson ;
import com.google.gson.TypeAdapter ;
import com.google.gson.TypeAdapterFactory ;
import com.google.gson.reflect.TypeToken ;
import com.google.gson.stream.JsonReader ;
import com.google.gson.stream.JsonWriter ;

/** 
 * This TypeAdapter unproxies Hibernate proxied objects, and serializes them 
 * through the registered (or default) TypeAdapter of the base class. 
 */
public class HibernateProxyTypeAdapter extends TypeAdapter<HibernateProxy> {
    
    public static final TypeAdapterFactory    FACTORY    = new TypeAdapterFactory() {
        @Override
        @SuppressWarnings("unchecked")
        public <T> TypeAdapter<T> create(Gson gson,
                TypeToken<T> type) {
            return (HibernateProxy.class
                    .isAssignableFrom(type
                            .getRawType()) ? (TypeAdapter<T>) new HibernateProxyTypeAdapter(
                    gson) : null) ;
        }
    } ;
                                                    
    private final Gson                        context ;
    
    private HibernateProxyTypeAdapter(Gson context) {
        this.context = context ;
    }
    
    @Override
    public HibernateProxy read(JsonReader in) throws IOException {
        throw new UnsupportedOperationException("Not supported") ;
    }
    
    @SuppressWarnings({ "rawtypes", "unchecked" })
    @Override
    public void write(JsonWriter out, HibernateProxy value) throws IOException {
        if (value == null) {
            out.nullValue() ;
            return ;
        }
        // Retrieve the original (not proxy) class
        Class<?> baseType = Hibernate.getClass(value) ;
        // Get the TypeAdapter of the original class, to delegate the
        // serialization
        TypeAdapter delegate = context.getAdapter(TypeToken.get(baseType)) ;
        // Get a filled instance of the original class
        Object unproxiedValue = ((HibernateProxy) value).getHibernateLazyInitializer()
                .getImplementation() ;
        // Serialize the value
        delegate.write(out, unproxiedValue) ;
    }
}

 

然后初始化gson對象的方式:

Gson gson = new GsonBuilder().setDateFormat("yyyy-MM-dd")
                                                    .registerTypeAdapterFactory(
                                                    HibernateProxyTypeAdapter.FACTORY).create() ;                

這樣就解決了,出現這個錯誤的主要原因是,hibernate采取懶加載的方式查詢數據庫,也就是只有用到了才去查真正的數據,用不到的話只是返回一個代理對象,gson識別不了代理對象,所以沒法轉換.