服务器端用Servlet响应客户端请求，Gson请求。可以返回多个数据库中的信息

Gson解析工具类GsonUtil，可以实现对象转换为Json字符串，也可以将json字符串转换为object

package gsonutil;import java.util.ArrayList;import java.util.List;import com.google.gson.Gson;import com.google.gson.GsonBuilder;import com.google.gson.reflect.TypeToken;public class GsonUtil<T> {    private static Gson gson = new Gson();    public static <T>  String objectToJsonStr(T object)    {        String jsonStr;        jsonStr = gson.toJson(object);        return jsonStr;    }    public static <T> String objectsToJsonStr(List<T> objects)    {        String jsonStr;        jsonStr = gson.toJson(objects);        return jsonStr;    }    public static <T> T jsonStrToObject(String jsonStr,Class<T> cla)    {        T object = gson.fromJson(jsonStr,cla);        return object;    }    public static <T> List<T> jsonStrToObjects(String jsonStr,Class<T> cla)    {        //json字符串不能为空          //json字符串必须为数组节点类型          List<T> listT = null;          try {              //创建泛型对象              T t =  cla.newInstance();              //利用类加载加载泛型的具体类型              Class<T> classT = (Class<T>) Class.forName(t.getClass().getName());              List<Object> listObj = new ArrayList<Object>();              //将数组节点中json字符串转换为object对象到Object的list集合              listObj = new GsonBuilder().create().fromJson(jsonStr, new TypeToken<List<Object>>(){}.getType());              //转换未成功              if(listObj == null || listObj.isEmpty()) return null;              listT = new ArrayList<T>();              //将Object的list中的的每一个元素中的json字符串转换为泛型代表的类型加入泛型代表的list集合返回              for (Object obj : listObj) {                  T perT = new GsonBuilder().create().fromJson(obj.toString(), classT);                  listT.add(perT);              }          } catch (Exception e) {              e.printStackTrace();          }          return listT;      }}

ProductInfo类，get,set方法实现获取产品id，name,path

package bean;public class ProductInfo {    private String img;    private String name;    private int id;    public ProductInfo() {    }    public ProductInfo( int id,String img, String name) {        this.img = img;        this.name = name;        this.id = id;    }    public String getImg() {        return img;    }    public void setImg(String img) {        this.img = img;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public int getId() {        return id;    }    public void setId(int id) {        this.id = id;    }}

ProductInfoDao类返回类对象prds，包含了数据库中的产品id，name，path信息

package db;import java.sql.Connection;import java.sql.ResultSet;import java.sql.SQLException;import java.sql.Statement;import java.util.ArrayList;import java.util.List;import bean.ProductInfo;public class ProductInfoDao {        int id = -1;        private DBConn db;        public ProductInfoDao() {            db = DBConn.getInstance();        }        public List<ProductInfo> getProductInfos() throws Exception {            List<ProductInfo> prds = new ArrayList<ProductInfo>();            try {                /*这种结果集不支持,滚动的读去功能所以,如果获得这样一个结果集,只能使用它里面的next()方法,逐个的读去数据.                 * 所以如果只是想要可以滚动的类型的Result只要把Statement如下赋值就行了.                    * Statement st=conn.createStatement(Result.TYPE_SCROLL_INSENITIVE,ResultSet.CONCUR_READ_ONLY);                 * */                Connection conn = db.getConnection();                Statement stat = conn.createStatement();                ResultSet rs = stat.executeQuery("SELECT * FROM product where prdId <=10");                while (rs.next())                {                  ProductInfo prd = new ProductInfo();                  prd.setId(rs.getInt(1));                  prd.setImg(rs.getString(2));                  prd.setName("haha"+rs.getInt(1));                  prds.add(prd);                  System.out.println(prd.getId());                  System.out.println(prd.getImg());                  System.out.println(prd.getName());                }                stat.close();                conn.close();                return prds;            } catch (SQLException e) {                System.out.println("查询失败！");                e.printStackTrace();            }            return null;        }               public static void main(String[] args) {            ProductInfoDao pDao=new ProductInfoDao();            try {                pDao.getProductInfos();            } catch (Exception e) {                // TODO Auto-generated catch block                e.printStackTrace();            }        }}

DBConn类实现数据库连接

package db;import java.io.File;import java.sql.*;public class DBConn {    private static DBConn db = null;    public static DBConn getInstance(){        if (db == null){            db = new DBConn();        }        return db;    }    //初始化数据库    private DBConn() {        Connection conn = null;        //System.out.println(new java.util.Date());        try {            conn = getConnection();            conn.setAutoCommit(false);            conn.commit();            conn.close();        } catch (SQLException e) {            System.out.println("数据库创建失败！");            e.printStackTrace();        }    }    //创建数据库连接    public Connection getConnection()    {        try        {              String driver = "com.mysql.jdbc.Driver";            // URL指向要访问的数据库名                     String url = "jdbc:mysql://127.0.0.1:3306/mall";            // MySQL配置时的用户名                String user = "root";              // MySQL配置时的密码               String password = "";            String sql=null;            File file=null;                Class.forName(driver);             // 连续数据库                         Connection conn = DriverManager.getConnection(url, user, password);                if(!conn.isClosed())                                 System.out.println("数据库连接成功");            return conn;        }        catch(Exception e)        {            System.out.println("数据库连接异常");            e.printStackTrace();            return null;        }    }/*public static void main(String[] args) {    DBConn dbConn =new DBConn();}*/}

ProductServlet类实现post方法向客户端响应请求

package servlet;import gsonutil.GsonUtil;import java.io.IOException;import java.util.ArrayList;import java.util.List;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.google.gson.Gson;import db.ProductInfoDao;import bean.ProductInfo;@SuppressWarnings("serial")public class ProductServlet extends HttpServlet{    String jsonStr;    ProductInfo prdInfo = new ProductInfo();    ProductInfoDao prdDao = new ProductInfoDao();    Gson gson = new Gson();    protected void doGet(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        doPost(req, resp);    }    protected void doPost(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        resp.setCharacterEncoding("utf-8");        resp.setContentType("text/html;Charset=utf-8");        List<ProductInfo> prds = null;        try {            prds = new ProductInfoDao().getProductInfos();        } catch (Exception e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        jsonStr =GsonUtil.objectToJsonStr(prds);        System.out.println(prds.size());        for(int i=0;i<prds.size();i++)        {            System.out.println(prds.get(i).getId()+"  "+prds.get(i).getImg()+"  "+prds.get(i).getName());        }        System.out.println("---------");        System.out.println(jsonStr);        resp.getWriter().print(jsonStr);    }}

实验结果