基于JDBC封装的BaseDao(实例代码)

基于JDBC封装的BaseDao(实例代码)

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 {

Connection conn;

PreparedStatement st;

ResultSet rs;

JdbcUtil jdbcUtil = new JdbcUtil();

int result = 0;

private Class persistentClass;

@SuppressWarnings("unchecked")

public BaseDaoUtil(){

conn = jdbcUtil.getConnection();

ParameterizedType type = (ParameterizedType) getClass().getGenericSuperclass();

persistentClass = (Class) type.getActualTypeArguments()[0];

}

/**

* 保存

* @param entity

* @return

*/

public int save(T entity) throws Exception{

String sql = "INSERT INTO "+ entity.getClass().getSimpleName().toLowerCase() +" (";

List list = this.matchPojoMethods(entity,"get");

Iterator 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 list = this.matchPojoMethods(entity, "set");

Iterator 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 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 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 list = this.matchPojoMethods(entity, "set");

Iterator 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 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 list = new ArrayList();

//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) {

http:// 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});

}

}

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