java中gson的简单使用

　　把从数据库中查询的记录以JSON格式返回给客户端，在这里使用gson-2.2.4.jar包。

代码结构如下：

数据库结构如下：

（1）User.java

public class User {
    private int id;
    private String name;
    private int age;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    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;
    }
}

(2)JdbcUtils.java

public class JdbcUtils {
    private static final String CLASS_NAME="com.mysql.jdbc.Driver";
    private static final String URL="jdbc:mysql://localhost:3306/test";
    private static final String USER="root";
    private static final String PWD="mysql";
    
    private JdbcUtils(){}
    
    static{
        try{
            Class.forName(CLASS_NAME);
        }catch(Exception e){
            e.printStackTrace();
        }
    }
    
    //建立数据库链接
    public static Connection getConn()throws Exception{
        return DriverManager.getConnection(URL,USER,PWD);
    }
    
    //释放资源
    public static void free(ResultSet rs,Statement st,Connection conn){
            try {
                if(rs!=null){
                    rs.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }finally{
                try {
                    if(st!=null){
                        st.close();
                    }
                } catch (SQLException e) {
                    e.printStackTrace();
                }finally{
                    try {
                        if(conn!=null){
                            conn.close();
                        }
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }
                }
            }
    }
}

(3)UserServer.java

public class UserServer {
    public static List<User> getUserList(){
        List<User> list=null;
        Connection conn=null;
        PreparedStatement ps=null;
        ResultSet rs=null;
        User user=null;
        String sql="select id,name,age from user";
        try {
            conn=JdbcUtils.getConn();
            ps=conn.prepareStatement(sql);
            rs=ps.executeQuery();
            list=new ArrayList<User>();
            while(rs.next()){
                user=new User();
                user.setId(rs.getInt("id"));
                user.setName(rs.getString("name"));
                user.setAge(rs.getInt("age"));
                list.add(user);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }finally{
            JdbcUtils.free(rs, ps, conn);
        }
        return list;
    }
}

(4)Test.java

public class Test {
    public static void main(String args[]){
        List<User>userList=UserServer.getUserList();
        if(userList!=null){
            Gson gson=new Gson();
            String jsonstr=gson.toJson(userList);
            System.out.println(jsonstr);
        }
    }
}

运行结果：

[
　　{"id":1,"name":"zhangsan","age":23},
　　{"id":2,"name":"lisi","age":25},
　　{"id":3,"name":"王五","age":25}
]