整合volley+greendao+gson，让android开发变得非常容易

最新推荐文章于 2021-07-28 17:30:36 发布

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本文介绍如何整合Volley、GreenDao和Gson实现Android平台上的高效网络通信、数据解析与本地数据库存储。通过具体示例展示了如何使用这些框架简化开发流程。

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一、框架介绍
         1、Volley
   Google I/O 2013上发布的用于Android平台的网络通信库，能使网络通信更快、更简单、更健壮。实际使用下来，确实感受非常好，如官方所说。他提供了如下的便利功能：
         JSON，图像等的异步下载；
         网络请求的优先级处理
   网络请求的排序
         缓存
       多级别取消请求

和Activity和生命周期的联动

下载：git clone https://android.googlesource.com/platform/frameworks/volley

2、GreenDao
目前android经常用的orm框架主要有greenDAO、OrmLite、AndrORM。综合了网上的各种评价，greenDAO的运行效率最高，内存消耗最少，性能最佳，支持一对多，多对多，且无需涉及sql语言。因此决定采用greenDAO框架，对项目的orm框架进行改进。

下载：git clone https://github.com/greenrobot/greenDAO.git

   3、Gson
   该框架也是出自Google，无需annotation就可以轻松将实体序列化，同时又可以通过annotation来灵活配置需要序列化的字段。

二、整合
   通过Volley获取服务器数据,通过gson将json数据转换成实体，通过GreenDao直接将实体存入sqlite数据库，使用时可直接从sqlite取出实体类。整个流程无需接触通信，数据库操作，且全部为实体操作，完全为java的编程习惯。

1、使用Volley、GreenDao从服务器获取数据转换成实体

一个简单request请求，该请求返回的是一个json对象

[java]view plaincopy 
   
 mQueue = Volley.newRequestQueue(getApplicationContext());    
 mQueue.add(new JsonObjectRequest(Method.GET, url, null,    
             new Listener() {    
                 @Override    
                 public void onResponse(JSONObject response) {    
                     Log.d(TAG, "response : " + response.toString());    
                 }    
             }, null));    
 mQueue.start();   

现在我们需要修改让其直接返回实体对象，首先需要一个GsonRequest，来处理返回的数据，将其转换成我们所要的对象

[java]view plaincopy 
   
 import java.io.UnsupportedEncodingException;  
 import java.util.Map;  
   
 import com.android.volley.AuthFailureError;  
 import com.android.volley.NetworkResponse;  
 import com.android.volley.ParseError;  
 import com.android.volley.Request;  
 import com.android.volley.Response;  
 import com.android.volley.Response.ErrorListener;  
 import com.android.volley.Response.Listener;  
 import com.android.volley.toolbox.HttpHeaderParser;  
 import com.google.gson.Gson;  
 import com.google.gson.JsonSyntaxException;  
   
 public class GsonRequest<T> extends Request<T> {  
     private final Gson gson = new Gson();  
     private final Class<T> clazz;  
     private final Map<String, String> headers;  
     private final Listener<T> listener;  
   
     /** 
      * Make a GET request and return a parsed object from JSON. 
      * 
      * @param url 
      *            URL of the request to make 
      * @param clazz 
      *            Relevant class object, for Gson's reflection 
      * @param headers 
      *            Map of request headers 
      */  
     public GsonRequest(String url, Class<T> clazz, Map<String, String> headers,  
             Listener<T> listener, ErrorListener errorListener) {  
         super(Method.GET, url, errorListener);  
         this.clazz = clazz;  
         this.headers = headers;  
         this.listener = listener;  
           
     }  
   
     @Override  
     public Map<String, String> getHeaders() throws AuthFailureError {  
         return headers != null ? headers : super.getHeaders();  
     }  
   
     @Override  
     protected void deliverResponse(T response) {  
         listener.onResponse(response);  
     }  
   
     @Override  
     protected Response<T> parseNetworkResponse(NetworkResponse response) {  
         try {  
             String json = new String(response.data,  
                     HttpHeaderParser.parseCharset(response.headers));  
             return Response.success(gson.fromJson(json, clazz),  
                     HttpHeaderParser.parseCacheHeaders(response));  
         } catch (UnsupportedEncodingException e) {  
             return Response.error(new ParseError(e));  
         } catch (JsonSyntaxException e) {  
             return Response.error(new ParseError(e));  
         }  
     }  
 }  

继承了Request，在parseNetworkResponse方法中，我们将服务器返回的数据通过gson转换为我们指定的实体类，支持各种类型的转换，包括数组（勿使用,数据库无法存储）、List、Map、对象等，字段名必须跟返回的字段名一致，且区分大小写

现在我们有了Request，就可以直接使用了

[java]view plaincopy 
   
 mRequestQueue.add(new GsonRequest<User>(url, User.class, null,    
     new Listener() {    
         public void onResponse(User response) {    
                 
             //TO DO    
         }    
     }    
 }    

现在我们直接得到实体类了，这时候可以直接使用，也可以保存到数据库

2、GreenDao的使用

GreenDao下载后有多个项目，DaoCore项目是需要导入的核心类库，DaoGenerator、DaoExampleGenerator为JAVA项目，用于生成项目使用的DAO及Bean，第一步我们使用它来生成DAO：

[java]view plaincopy 
   
 package de.greenrobot.daogenerator.gentest;  
 import de.greenrobot.daogenerator.DaoGenerator;  
 import de.greenrobot.daogenerator.Entity;  
 import de.greenrobot.daogenerator.Property;  
 import de.greenrobot.daogenerator.Schema;  
 import de.greenrobot.daogenerator.ToMany;  
 /** 
  * Generates entities and DAOs for the example project DaoExample. 
  * 
  * Run it as a Java application (not Android). 
  * 
  * @author Markus 
  */  
 public class ExampleDaoGenerator  
 {  
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
     public static void main(String[] args) throws Exception  
     {  
         Schema schema = new Schema(3, "de.greenrobot.daoexample");  
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
         addNote(schema);  
         addCustomerOrder(schema);  
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
         new DaoGenerator().generateAll(schema, "../DaoExample/src-gen");  
     }  
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
     private static void addNote(Schema schema)  
     {  
         Entity note = schema.addEntity("Note");  
         note.addIdProperty();  
         note.addStringProperty("text").notNull();  
         note.addStringProperty("comment");  
         note.addDateProperty("date");  
     }  
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
     private static void addCustomerOrder(Schema schema)  
     {  
         Entity customer = schema.addEntity("Customer");  
         customer.addIdProperty();  
         customer.addStringProperty("name").notNull();  
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
         Entity order = schema.addEntity("Order");  
         order.setTableName("ORDERS"); // "ORDER" is a reserved keyword  
         order.addIdProperty();  
         Property orderDate = order.addDateProperty("date").getProperty();  
         Property customerId = order.addLongProperty("customerId").notNull().getProperty();  
         order.addToOne(customer, customerId);  
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
         ToMany customerToOrders = customer.addToMany(order, customerId);  
         customerToOrders.setName("orders");  
         customerToOrders.orderAsc(orderDate);  
     }  
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
 }  

生成代码很简单，网上也说的很多，自己看一下就可以完成,接下来我们就需要在代码中获取Dao，可以把他放在Application中

[java]view plaincopy 
   
 public static DaoMaster getDaoMaster(Context context) {  
   
     if (daoMaster == null) {  
         OpenHelper helper = new DaoMaster.DevOpenHelper(context, dir  
                 + Constants.DB_NAME, null);  
         daoMaster = new DaoMaster(helper.getWritableDatabase());  
   
     }  
     return daoMaster;  
     }  
   
 public static DaoSession getDaoSession(Context context) {  
     if (daoSession == null) {  
         if (daoMaster == null)  
             daoMaster = getDaoMaster(context);  
         daoSession = daoMaster.newSession();  
     }  
     return daoSession;  
 }  

现在我们该有的都有了，就可以操作数据库了

1、查询

范例1：查询是否包含某个ID

[java]view plaincopy 
   
 <span style="color:#000000;">public boolean isSaved(int ID)  
 {  
     QueryBuilder<SaveList> qb = saveListDao.queryBuilder();  
     qb.where(Properties.Id.eq(ID));  
     qb.buildCount().count();  
     return qb.buildCount().count() > 0 ? true : false;  
 }</span>  

范例2：获取整个表的数据集合,一句代码就搞定！

[java]view plaincopy 
   
 public List<PhotoGalleryDB> getPhotoGallery()  
 {  
     return photoGalleryDao.loadAll();// 获取图片相册  
 }  

范例3：通过一个字段值查找对应的另一个字段值(为简便直接使用下面方法，也许有更简单的方法，尚未尝试)

[java]view plaincopy 
   
 /** 通过图片id查找其目录id */  
 public int getTypeId(int picId)  
 {  
     QueryBuilder<PhotoGalleryDB> qb = photoGalleryDao.queryBuilder();  
     qb.where(Properties.Id.eq(picId));  
     if (qb.list().size() > 0)  
     {  
         return qb.list().get(0).getTypeId();  
     }  
     else  
     {  
         return -1;  
     }  
 }  

范例4：查找所有第一姓名是“Joe”并且以lastname排序。

[java]view plaincopy 
    
 List joes = userDao.queryBuilder()  
 .where(Properties.FirstName.eq("Joe"))  
 .orderAsc(Properties.LastName)  
 .list();  

2.增添/插入、修改

插入数据更加简单，也是只要一句代码便能搞定!

[java]view plaincopy 
    
 public void addToPhotoTable(Photo p)  
 {  
     photoDao.insert(p);  
 }  

插入时需要new一个新的对象，范例如下:

[java]view plaincopy 
    
 DevOpenHelper helper = new DaoMaster.DevOpenHelper(this, "notes-db", null);  
 db = helper.getWritableDatabase();  
 daoMaster = new DaoMaster(db);  
 daoSession = daoMaster.newSession();  
 noteDao = daoSession.getNoteDao();  
 Note note = new Note(null, noteText, comment, new Date());  
 noteDao.insert(note);  

修改更新：

[java]view plaincopy 
     
 photoDao.insertOrReplace(photo);  
 photoDao.insertInTx(photo);  

3.删除:

(1)清空表格数据

[java]view plaincopy 
     
 /** 清空相册图片列表的数据 */  
 public void clearPhoto()  
 {  
     photoDao.deleteAll();  
 }  

(2)删除某个对象

[java]view plaincopy 
     
 public void deleteCityInfo(int cityId)  
 {  
     QueryBuilder<DBCityInfo> qb = cityInfoDao.queryBuilder();  
     DeleteQuery<DBCityInfo> bd = qb.where(Properties.CityId.eq(cityId)).buildDelete();  
     bd.executeDeleteWithoutDetachingEntities();  
 }  