最近闲暇时萌发写一写dao的封装的例子，就将以前写的整理一下。
public class BaseDao<T> {
Connection conn;
PreparedStatement st;
ResultSet rs;
JdbcUtil jdbcUtil = new JdbcUtil();
int result = 0;
private Class<T> persistentClass;
@SuppressWarnings("unchecked")
public BaseDaoUtil(){
conn = jdbcUtil.getConnection();
ParameterizedType type = (ParameterizedType) getClass().getGenericSuperclass();
persistentClass = (Class<T>) type.getActualTypeArguments()[0];
}
/**
* 保存
* @param entity
* @return
*/
public int save(T entity) throws Exception{
String sql = "INSERT INTO "+ entity.getClass().getSimpleName().toLowerCase() +" (";
List<Method> list = this.matchPojoMethods(entity,"get");
Iterator<Method> iter = list.iterator();
Object obj[] = new Object[list.size()];
int i = 0;
//拼接字段顺序 insert into table name(id,name,email,
while(iter.hasNext()) {
Method method = iter.next();
sql += method.getName().substring(3).toLowerCase() + ",";
if (method.getReturnType().getSimpleName().indexOf("Date") !=-1) {
SimpleDateFormat sbf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
obj[i] = sbf.format(method.invoke(entity, new Object[]{}));
}else {
obj[i] = method.invoke(entity, new Object[]{});
}
i++;
}
//去掉最后一个,符号insert insert into table name(id,name,email) values(
sql = sql.substring(0, sql.lastIndexOf(",")) + ") values(";
//拼装预编译SQL语句insert insert into table name(id,name,email) values(?,?,?,
for(int j = 0; j < list.size(); j++) {
sql += "?,";
}
//去掉SQL语句最后一个,符号insert insert into table name(id,name,email) values(?,?,?);
sql = sql.substring(0, sql.lastIndexOf(",")) + ")";
//到此SQL语句拼接完成,打印SQL语句
System.out.println(sql);
try {
st = conn.prepareStatement(sql);
for (int j = 0; j < obj.length; j++) {
st.setObject(j+1, obj[j]);
}
result = st.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
}
jdbcUtil.getClose(rs, st, conn);
return result;
}
/**
* 删除
* @param object
* @return
* @throws SQLException
*/
public int deleteId(Object object) throws Exception{
String sql = "delete from "+ persistentClass.getSimpleName().toLowerCase() +" where ";
//通过子类的构造函数,获得参数化类型的具体类型.比如BaseDAO<T>也就是获得T的具体类型
T entity = persistentClass.newInstance();
//存放Pojo(或被操作表)主键的方法对象
Method idMethod = null;
List<Method> list = this.matchPojoMethods(entity, "set");
Iterator<Method> iter = list.iterator();
//过滤取得Method对象
while(iter.hasNext()) {
Method tempMethod = iter.next();
if(tempMethod.getName().indexOf("Id") != -1 && tempMethod.getName().substring(3).length() == 2) {
idMethod = tempMethod;
} else if((entity.getClass().getSimpleName() + "Id").equalsIgnoreCase(tempMethod.getName().substring(3))){
idMethod = tempMethod;
}
}
//第一个字母转为小写
sql += idMethod.getName().substring(3,4).toLowerCase()+idMethod.getName().substring(4) + " = ?";
System.out.println(sql);
st = conn.prepareStatement(sql);
//判断id的类型
if(object instanceof Integer) {
st.setInt(1, (Integer)object);
} else if(object instanceof String){
st.setString(1, (String)object);
}
result = st.executeUpdate();
jdbcUtil.getClose(rs, st, conn);
return result;
}
/**
* 修改
* @param entity
* @return
* @throws Exception
*/
public int update(T entity) throws Exception{
String sql = "update "+ entity.getClass().getSimpleName().toLowerCase() +" set ";
List<Method> list = this.matchPojoMethods(entity, "get");
//装载参数
Object obj[] = new Object[list.size()];
int i = 0;
//临时Method对象,负责迭代时装method对象.
Method tempMethod = null;
//由于修改时不需要修改ID,所以按顺序加参数则应该把Id移到最后.
Method idMethod = null;
Iterator<Method> iter = list.iterator();
while(iter.hasNext()) {
tempMethod = iter.next();
//如果方法名中带有ID字符串并且长度为2,则视为ID.
if(tempMethod.getName().lastIndexOf("Id") != -1 && tempMethod.getName().substring(3).length() == 2) {
obj[list.size()-1] = tempMethod.invoke(entity, new Object[]{});
//把ID字段的对象存放到一个变量中,然后在集合中删掉.
idMethod = tempMethod;
iter.remove();
//如果方法名去掉set/get字符串以后与pojo + "id"想符合(大小写不敏感),则视为ID
} else if((entity.getClass().getSimpleName() + "Id").equalsIgnoreCase(tempMethod.getName().substring(3))) {
obj[list.size()-1] = tempMethod.invoke(entity, new Object[]{});
idMethod = tempMethod;
iter.remove();
}
}
//把迭代指针移到第一位
iter = list.iterator();
while(iter.hasNext()) {
tempMethod = iter.next();
sql += tempMethod.getName().substring(3).toLowerCase() + "= ?,";
obj[i] = tempMethod.invoke(entity, new Object[]{});
i++;
}
//去掉最后一个,符号
sql = sql.substring(0,sql.lastIndexOf(","));
//添加条件
sql += " where " + idMethod.getName().substring(3).toLowerCase() + " = ?";
//SQL拼接完成,打印SQL语句
System.out.println(sql);
st = conn.prepareStatement(sql);
for (int j = 0; j < obj.length; j++) {
st.setObject(j+1, obj[j]);
}
result = st.executeUpdate();
jdbcUtil.getClose(rs, st, conn);
return result;
}
public T findById(Object object) throws Exception{
String sql = "select * from "+ persistentClass.getSimpleName().toLowerCase() +" where ";
//通过子类的构造函数,获得参数化类型的具体类型.比如BaseDAO<T>也就是获得T的具体类型
T entity = persistentClass.newInstance();
//存放Pojo(或被操作表)主键的方法对象
Method idMethod = null;
List<Method> list = this.matchPojoMethods(entity, "set");
Iterator<Method> iter = list.iterator();
//过滤取得Method对象
while(iter.hasNext()) {
Method tempMethod = iter.next();
if(tempMethod.getName().indexOf("Id") != -1 && tempMethod.getName().substring(3).length() == 2) {
idMethod = tempMethod;
} else if((entity.getClass().getSimpleName() + "Id").equalsIgnoreCase(tempMethod.getName().substring(3))){
idMethod = tempMethod;
}
}
//第一个字母转为小写
sql += idMethod.getName().substring(3,4).toLowerCase()+idMethod.getName().substring(4) + " = ?";
System.out.println(sql);
st = conn.prepareStatement(sql);
//判断id的类型
if(object instanceof Integer) {
st.setInt(1, (Integer)object);
} else if(object instanceof String){
st.setString(1, (String)object);
}
rs = st.executeQuery();
//把指针指向迭代器第一行
iter = list.iterator();
//封装
while(rs.next()) {
while(iter.hasNext()) {
Method method = iter.next();
if(method.getParameterTypes()[0].getSimpleName().indexOf("String") != -1) {
//由于list集合中,method对象取出的方法顺序与数据库字段顺序不一致(比如:list的第一个方法是setDate,而数据库按顺序取的是"123"值)
//所以数据库字段采用名字对应的方式取.
this.setString(method, entity, rs.getString(method.getName().substring(3).toLowerCase()));
} else if(method.getParameterTypes()[0].getSimpleName().indexOf("Date") != -1){
this.setDate(method, entity, rs.getDate(method.getName().substring(3).toLowerCase()));
}else {
this.setInt(method, entity, rs.getInt(method.getName().substring(3).toLowerCase()));
}
}
}
jdbcUtil.getClose(rs, st, conn);
return entity;
}
/**
* 过滤当前Pojo类所有带传入字符串的Method对象,返回List集合.
*/
private List<Method> matchPojoMethods(T entity,String methodName) {
//获得当前Pojo所有方法对象
Method[] methods = entity.getClass().getDeclaredMethods();
//List容器存放所有带get字符串的Method对象
List<Method> list = new ArrayList<Method>();
//过滤当前Pojo类所有带get字符串的Method对象,存入List容器
for(int index = 0; index < methods.length; index++) {
if(methods[index].getName().indexOf(methodName) != -1) {
list.add(methods[index]);
}
}
return list;
}
/**
* 参数类型为String时,为entity字段设置参数,对应set
*/
public String setString(Method method, T entity, String arg) throws Exception{
return (String)method.invoke(entity, new Object[]{arg});
}
/**
* 参数类型为Date时,为entity字段设置参数,对应set
*/
public Date setDate(Method method, T entity, Date arg) throws Exception{
return (Date)method.invoke(entity, new Object[]{arg});
}
/**
* 参数类型为Integer或int时,为entity字段设置参数,对应set
*/
public Integer setInt(Method method, T entity, Integer arg) throws Exception{
return (Integer)method.invoke(entity, new Object[]{arg});
}
}
以上这篇基于JDBC封装的BaseDao(实例代码)就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持菜鸟教程(cainiaojc.com)。