依靠反射来个Dbutils

闲来无事，写个dbutils玩玩，不完善，满足基本增删改查，上代码

1、Dbutils

 package db;

 import annotation.Table;
 import java.util.*;
 import java.sql.*;
 import java.lang.reflect.Field;

 /**
  *
  * @author xjy
  * @param <T>
  */
 public class DbUtil<T> {

     private static DataBase dataBase = null;
     private static Connection con = null;
     private static Statement st = null;

     public DbUtil() {
         dataBase = new DataBase();
     }

     @SuppressWarnings("null")
     public List<T> getAll(T bean) throws Exception {

         List<T> list = new ArrayList<>();
         Class<T> clazz = (Class<T>) bean.getClass();
         Table table = clazz.getDeclaredAnnotation(Table.class);
         String name = table.name();

         String tableName;
         if (!"".equals(name)) {
             tableName = name;
         } else {
             tableName = clazz.getSimpleName().toLowerCase();
         }

         StringBuilder sql = new StringBuilder("select * from " + tableName);

         if (bean != null) {
             sql.append(" where ");
             Field[] declaredFields = clazz.getDeclaredFields();

             for (Field declaredField : declaredFields) {
                 //打开私有访问
                 declaredField.setAccessible(true);
                 String name1 = declaredField.getName();
                 Object value = declaredField.get(bean);
                 if (value != null && !"id".equals(name1)) {
                     sql.append(name1).append("='").append(value).append("' and ");
                 }
             }
             sql.append("1=1");
         }

         con = dataBase.getConnection();
         st = dataBase.getStatement();

         ResultSet rs = st.executeQuery(sql.toString());

         Field[] fields = clazz.getDeclaredFields();
         while (rs.next()) {

             T t = clazz.newInstance();

             for (Field field : fields) {
                 String fName = field.getName();
                 String str = rs.getString(fName);
                 field.setAccessible(true);

                 // 如果类型是Integer
                 if (field.getGenericType().toString().equals("class java.lang.Integer")) {
                     field.set(t, Integer.valueOf(str));
                 } else {
                     field.set(t, str);
                 }

             }

             list.add(t);
         }

         return list;
     }

     public int add(T bean) throws Exception {
         con = dataBase.getConnection();
         st = dataBase.getStatement();
         Class<T> clazz = (Class<T>) bean.getClass();
         Table table = clazz.getDeclaredAnnotation(Table.class);
         String name = table.name();

         String tableName;
         if (!"".equals(name)) {
             tableName = name;
         } else {
             tableName = clazz.getSimpleName().toLowerCase();
         }

         Field[] fields = clazz.getDeclaredFields();

         StringBuilder sql = new StringBuilder("insert into " + tableName + "(");

         for (Field field : fields) {
             String fName = field.getName();
             if (!"id".equals(fName)) {
                 sql.append(fName).append(",");

             }
         }

         sql.deleteCharAt(sql.length() - 1).append(") values(");

         Field[] declaredFields = clazz.getDeclaredFields();

         for (Field declaredField : declaredFields) {

             if (!"id".equals(declaredField.getName())) {
                 //打开私有访问
                 declaredField.setAccessible(true);
                 Object value = declaredField.get(bean);
                 sql.append("'").append(value).append("',");
             }

         }

         sql.deleteCharAt(sql.length() - 1).append(")");
         int result = 0;

         try {
             result = st.executeUpdate(sql.toString());
         } catch (SQLException se) {
             System.out.println(se.getMessage());
         } finally {

         }
         return result;
     }

     @SuppressWarnings("FinallyDiscardsException")
     public List<Map<String, Object>> querySql(String sql) {
         List<Map<String, Object>> list = new ArrayList<>();

         con = dataBase.getConnection();
         st = dataBase.getStatement();
         @SuppressWarnings("UnusedAssignment")
         ResultSet rs = null;
         try {
             rs = st.executeQuery(sql);
             ResultSetMetaData md = rs.getMetaData(); //获得结果集结构信息,元数据
             int columnCount = md.getColumnCount();   //获得列数
             while (rs.next()) {
                 Map<String, Object> rowData = new HashMap<>();
                 for (int i = 1; i <= columnCount; i++) {
                     rowData.put(md.getColumnName(i), rs.getObject(i));
                 }
                 list.add(rowData);
             }
         } catch (SQLException e) {
             System.out.println(e.toString());

         } finally {
             dataBase.closeConnection();
             return list;
         }
     }

     @SuppressWarnings("FinallyDiscardsException")
     public int executeSql(String sql) {
         con = dataBase.getConnection();
         st = dataBase.getStatement();
         int result = 0;
         try {
             result = st.executeUpdate(sql);
         } catch (SQLException se) {
             System.out.println(se.getMessage());
         } finally {
             dataBase.closeConnection();
             return result;
         }
     }

     @SuppressWarnings("MismatchedReadAndWriteOfArray")
     public int update(T bean) throws Exception {
         con = dataBase.getConnection();
         st = dataBase.getStatement();
         Class<T> clazz = (Class<T>) bean.getClass();
         Table table = clazz.getDeclaredAnnotation(Table.class);
         String name = table.name();

         String tableName;
         if (!"".equals(name)) {
             tableName = name;
         } else {
             tableName = clazz.getSimpleName().toLowerCase();
         }

         StringBuilder sql = new StringBuilder("update " + tableName + " set ");

         Field[] declaredFields = clazz.getDeclaredFields();

         for (Field declaredField : declaredFields) {
             declaredField.setAccessible(true);
             //打开私有访问
             String name1 = declaredField.getName();
             Object value = declaredField.get(bean);
             if (value != null && !"id".equals(name1)) {
                 sql.append(name1).append("='").append(value).append("',");
             }
         }
         Field field1 = clazz.getDeclaredField("id");
         field1.setAccessible(true);

         sql.deleteCharAt(sql.length() - 1).append(" where id =").append(field1.get(bean));

         int result = 0;

         try {
             result = st.executeUpdate(sql.toString());
         } catch (SQLException se) {
             System.out.println(se.getMessage());
         } finally {
         }
         return result;
     }
 }

2、注解Table

 package annotation;

 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;

 /**
  *
  * @author xjy
  */
 @Target(ElementType.TYPE)
 @Retention(RetentionPolicy.RUNTIME)
 public @interface Table {

     public String name() default "";

 }

3、database，获取连接等，这里用的sqlserver，其他自己发挥咯

 package db;

 import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.SQLException;
 import java.sql.Statement;

 /**
  *
  * @author Administrator
  */
 public class DataBase {

     private String driverName = "com.microsoft.sqlserver.jdbc.SQLServerDriver";
     String url = "jdbc:sqlserver://127.0.0.1:1433;databaseName=db_car";
     private String userName = "sa";
     private String userPasswd = "123456";
     private Connection connection;
     private Statement statement;
     public DataBase(){
         try {
             Class.forName(driverName);
         }
         catch (ClassNotFoundException cnfex){
             System.err.println("装载 JDBC/ODBC 驱动程序失败。");
             cnfex.printStackTrace();
             System.exit(1);
         }
     }
     //取得与数据库的连接
     public Connection getConnection(){
         try {
             //捕获连接数据库异常
             connection = DriverManager.getConnection(url, userName, userPasswd);
         }
         catch (SQLException sqlex){
             System.err.println("无法连接数据库");
             sqlex.printStackTrace();
             System.exit(1);
         }
         finally {
             return connection;
         }
     }
     //取得 statement
     public Statement getStatement(){
         try {
             if (connection != null){
             statement = connection.createStatement();
             }
         }
         catch (SQLException sqlex){
             System.err.println("无法取得 Statement");
             sqlex.printStackTrace();
             System.exit(1);
         }
         finally{
             return statement;
         }
     }
     public void closeConnection(){
         try {
             if (null != statement){
                 statement.close();
             }
             if (null != connection){
                 connection.close();
             }
             statement = null;
             connection = null;
             }
             catch (Exception e){
                 e.printStackTrace();
             }
         }
     }

所需驱动文件：https://files.cnblogs.com/files/xujingyang/sqljdbc4.zip

顺便说下，开发工具玩的是NetBeans