Java -- JDBC 学习--使用 DBUtils

Apache—DBUtils简介

commons-dbutils 是 Apache 组织提供的一个开源 JDBC工具类库，它是对JDBC的简单封装，学习成本极低，并且使用dbutils能极大简化jdbc编码的工作量，同时也不会影响程序的性能。
API介绍：
org.apache.commons.dbutils.QueryRunner
org.apache.commons.dbutils.ResultSetHandler
工具类
org.apache.commons.dbutils.DbUtils

如下利用DbUtils进行常用操作的封装：

DAO接口：

import java.sql.Connection;
import java.sql.SQLException;
import java.util.List;

/**
* 访问数据的 DAO 接口.
* 里边定义好访问数据表的各种方法
* @param T: DAO 处理的实体类的类型.
*/
public interface DAO<T> {

/**
* 批量处理的方法
* @param connection
* @param sql
* @param args: 填充占位符的 Object [] 类型的可变参数.
* @throws SQLException
*/
void batch(Connection connection,
String sql, Object [] ... args) throws SQLException;

/**
* 返回具体的一个值, 例如总人数, 平均工资, 某一个人的 email 等.
* @param connection
* @param sql
* @param args
* @return
* @throws SQLException
*/
<E> E getForValue(Connection connection,
String sql, Object ... args) throws SQLException;

/**
* 返回 T 的一个集合
* @param connection
* @param sql
* @param args
* @return
* @throws SQLException
*/
List<T> getForList(Connection connection,
String sql, Object ... args) throws SQLException;

/**
* 返回一个 T 的对象
* @param connection
* @param sql
* @param args
* @return
* @throws SQLException
*/
T get(Connection connection, String sql,
Object ... args) throws SQLException;

/**
* INSRET, UPDATE, DELETE
* @param connection: 数据库连接
* @param sql: SQL 语句
* @param args: 填充占位符的可变参数.
* @throws SQLException
*/
void update(Connection connection, String sql,
Object ... args) throws SQLException;

}

实现DAO类：

import java.sql.Connection;
import java.sql.SQLException;
import java.util.List;

import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import org.apache.commons.dbutils.handlers.ScalarHandler;

/**
* 使用 QueryRunner 提供其具体的实现
* @param <T>: 子类需传入的泛型类型.
*/
public class JdbcDaoImpl<T> implements DAO<T> {

private QueryRunner queryRunner = null;
private Class<T> type;

public JdbcDaoImpl() {
queryRunner = new QueryRunner();
type = ReflectionUtils.getSuperGenericType(getClass());
}

@Override
public void batch(Connection connection, String sql, Object[]... args) throws SQLException {
queryRunner.batch(connection, sql, args);
}

@Override
public <E> E getForValue(Connection connection, String sql, Object... args) throws SQLException {
return (E) queryRunner.query(connection, sql, new ScalarHandler(), args);
}

@Override
public List<T> getForList(Connection connection, String sql, Object... args)
throws SQLException {
return queryRunner.query(connection, sql,
new BeanListHandler<>(type), args);
}

@Override
public T get(Connection connection, String sql, Object... args) throws SQLException {
return queryRunner.query(connection, sql,
new BeanHandler<>(type), args);
}

@Override
public void update(Connection connection, String sql, Object... args) throws SQLException {
queryRunner.update(connection, sql, args);
}

}

public class CustomerDao
extends JdbcDaoImpl<Customer>{

}

Customer.java对象类：

import java.sql.Date;

public class Customer {

private Integer id;
private String name;
private String email;
private Date birth;

public Integer getId() {
return id;
}

public void setId(Integer id) {
this.id = id;
}

public String getCustomerName() {
return name;
}

public void setCustomerName(String name) {
this.name = name;
}

public String getEmail() {
return email;
}

public void setEmail(String email) {
this.email = email;
}

public Date getBirth() {
return birth;
}

public void setBirth(Date birth) {
this.birth = birth;
}

@Override
public String toString() {
return "Customer [id=" + id + ", name=" + name + ", email=" + email
+ ", birth=" + birth + "]";
}

public Customer(Integer id, String name, String email, Date birth) {
super();
this.id = id;
this.name = name;
this.email = email;
this.birth = birth;
}

public Customer() {
// TODO Auto-generated constructor stub
}

}

调用示例：

@Test
public void testGet() {
Connection connection = null;

try {
connection = JDBCTools.getConnection();
String sql = "SELECT id, name customerName, " +
"email, birth FROM customers " +
"WHERE id = ?";
Customer customer = customerDao.get(connection, sql, 5);
System.out.println(customer);
} catch (Exception e) {
e.printStackTrace();
} finally{
JDBCTools.releaseDB(null, null, connection);
}
}

相关反射类：

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;

/**
* 反射的 Utils 函数集合
* 提供访问私有变量, 获取泛型类型 Class, 提取集合中元素属性等 Utils 函数
* @author Administrator
*
*/
public class ReflectionUtils {

/**
* 通过反射, 获得定义 Class 时声明的父类的泛型参数的类型
* 如: public EmployeeDao extends BaseDao<Employee, String>
* @param clazz
* @param index
* @return
*/
@SuppressWarnings("unchecked")
public static Class getSuperClassGenricType(Class clazz, int index){
Type genType = clazz.getGenericSuperclass();

if(!(genType instanceof ParameterizedType)){
return Object.class;
}

Type [] params = ((ParameterizedType)genType).getActualTypeArguments();

if(index >= params.length || index < 0){
return Object.class;
}

if(!(params[index] instanceof Class)){
return Object.class;
}

return (Class) params[index];
}

/**
* 通过反射, 获得 Class 定义中声明的父类的泛型参数类型
* 如: public EmployeeDao extends BaseDao<Employee, String>
* @param <T>
* @param clazz
* @return
*/
@SuppressWarnings("unchecked")
public static<T> Class<T> getSuperGenericType(Class clazz){
return getSuperClassGenricType(clazz, 0);
}

/**
* 循环向上转型, 获取对象的 DeclaredMethod
* @param object
* @param methodName
* @param parameterTypes
* @return
*/
public static Method getDeclaredMethod(Object object, String methodName, Class<?>[] parameterTypes){

for(Class<?> superClass = object.getClass(); superClass != Object.class; superClass = superClass.getSuperclass()){
try {
//superClass.getMethod(methodName, parameterTypes);
return superClass.getDeclaredMethod(methodName, parameterTypes);
} catch (NoSuchMethodException e) {
//Method 不在当前类定义, 继续向上转型
}
//..
}

return null;
}

/**
* 使 filed 变为可访问
* @param field
*/
public static void makeAccessible(Field field){
if(!Modifier.isPublic(field.getModifiers())){
field.setAccessible(true);
}
}

/**
* 循环向上转型, 获取对象的 DeclaredField
* @param object
* @param filedName
* @return
*/
public static Field getDeclaredField(Object object, String filedName){

for(Class<?> superClass = object.getClass(); superClass != Object.class; superClass = superClass.getSuperclass()){
try {
return superClass.getDeclaredField(filedName);
} catch (NoSuchFieldException e) {
//Field 不在当前类定义, 继续向上转型
}
}
return null;
}

/**
* 直接调用对象方法, 而忽略修饰符(private, protected)
* @param object
* @param methodName
* @param parameterTypes
* @param parameters
* @return
* @throws InvocationTargetException
* @throws IllegalArgumentException
*/
public static Object invokeMethod(Object object, String methodName, Class<?> [] parameterTypes,
Object [] parameters) throws InvocationTargetException{

Method method = getDeclaredMethod(object, methodName, parameterTypes);

if(method == null){
throw new IllegalArgumentException("Could not find method [" + methodName + "] on target [" + object + "]");
}

method.setAccessible(true);

try {
return method.invoke(object, parameters);
} catch(IllegalAccessException e) {
System.out.println("不可能抛出的异常");
}

return null;
}

/**
* 直接设置对象属性值, 忽略 private/protected 修饰符, 也不经过 setter
* @param object
* @param fieldName
* @param value
*/
public static void setFieldValue(Object object, String fieldName, Object value){
Field field = getDeclaredField(object, fieldName);

if (field == null)
throw new IllegalArgumentException("Could not find field [" + fieldName + "] on target [" + object + "]");

makeAccessible(field);

try {
field.set(object, value);
} catch (IllegalAccessException e) {
System.out.println("不可能抛出的异常");
}
}

/**
* 直接读取对象的属性值, 忽略 private/protected 修饰符, 也不经过 getter
* @param object
* @param fieldName
* @return
*/
public static Object getFieldValue(Object object, String fieldName){
Field field = getDeclaredField(object, fieldName);

if (field == null)
throw new IllegalArgumentException("Could not find field [" + fieldName + "] on target [" + object + "]");

makeAccessible(field);

Object result = null;

try {
result = field.get(object);
} catch (IllegalAccessException e) {
System.out.println("不可能抛出的异常");
}

return result;
}
}