笔记如下
- 需要导入的jar包
c3p0-0.9.1.2.jar
mysql-connector-java-5.1.45-bin.jar -
包结构
2.png
3.png
- DbAssist.java
核心类
/*
* 承诺: 有一个增删改的方法,一个用于完成查询的方法,还有个接口
*
*/
public class DBAssist {
private DataSource ds;
public DBAssist(DataSource ds) {
this.ds = ds;
}
//这个方法完成增删改操作
public void update(String sql,Object[] args) {
Connection conn = null;
PreparedStatement stmt = null;
try {
conn = ds.getConnection();
stmt = conn.prepareStatement(sql);
ParameterMetaData pmd = stmt.getParameterMetaData();
//拿到占位符个数
int count = pmd.getParameterCount();
//替换占位符
if (count>0) {
//说明有占位符
if(args == null) {
throw new IllegalAccessException("你的占位符有问提,不要乱搞");
}
if(count!=args.length) {
throw new IllegalAccessException("你的占位符个数不匹配,不要乱搞");
}
//for循环去替换占位符
for (int i = 0; i < args.length; i++) {
stmt.setObject(i+1, args[i]);
}
}
//执行操作
stmt.executeUpdate();
} catch (Exception e) {
e.printStackTrace();
//自定义异常 ,一般继承RuntimeException
throw new MyRuntimeException(e);
}finally {
release(null, stmt, conn);
}
}
//用这个方法实现查找
public Object query(String sql,Object[] args,ResuletSetHandler rsh) {
Connection conn = null;
PreparedStatement stmt = null;
ResultSet rs = null;
try {
conn = ds.getConnection();
stmt = conn.prepareStatement(sql);
ParameterMetaData pmd = stmt.getParameterMetaData();
//拿到占位符个数
int count = pmd.getParameterCount();
//替换占位符
if (count>0) {
//说明有占位符
if(args == null) {
throw new IllegalAccessException("你的占位符有问提,不要乱搞");
}
if(count!=args.length) {
throw new IllegalAccessException("你的占位符个数不匹配,不要乱搞");
}
//for循环去替换占位符
for (int i = 0; i < args.length; i++) {
stmt.setObject(i+1, args[i]);
}
}
//执行操作
//需要告诉调用者自己去操作了....,所以要自己去定义一个接口
rs = stmt.executeQuery();
/*
*
*
*/
return rsh.handle(rs);
} catch (Exception e) {
e.printStackTrace();
//自定义异常 ,一般继承RuntimeException
throw new MyRuntimeException(e);
}finally {
release(null, stmt, conn);
}
}
//释放资源
public static void release(ResultSet rs ,Statement stmt, Connection conn) {
if(rs != null) {
try {
//释放获得的资源
rs.close();
} catch (SQLException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
//设置为空:斩断引用的对象
//有利于回收垃圾
rs = null;
}
if(stmt != null) {
try {
stmt.close();
} catch (SQLException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
stmt = null;
}
if(conn != null) {
try {
conn.close();
} catch (SQLException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
conn = null;
}
}
}
- MyRuntimeException.java
public class MyRuntimeException extends RuntimeException {
public MyRuntimeException() {
// TODO Auto-generated constructor stub
}
public MyRuntimeException(String message) {
super(message);
// TODO Auto-generated constructor stub
}
public MyRuntimeException(Throwable cause) {
super(cause);
// TODO Auto-generated constructor stub
}
public MyRuntimeException(String message, Throwable cause) {
super(message, cause);
// TODO Auto-generated constructor stub
}
public MyRuntimeException(String message, Throwable cause, boolean enableSuppression, boolean writableStackTrace) {
super(message, cause, enableSuppression, writableStackTrace);
// TODO Auto-generated constructor stub
}
}
- ResuletSetHandler.java
查询接口
public interface ResuletSetHandler {
Object handle(ResultSet rs);
}
- BeanHandler.java
public class BeanHandler implements ResuletSetHandler {
private Class clazz;
public BeanHandler(Class clazz) {
this.clazz = clazz;
}
@Override
public Object handle(ResultSet rs) {
try {
ResultSetMetaData rsmd = rs.getMetaData();
Object bean = clazz.newInstance();
if(rs.next()) {
//目标要封装的bean
int columnCount = rsmd.getColumnCount();
for (int i = 0; i < columnCount; i++) {
//拿到当前i ,这列的值
Object value = rs.getObject(i+1);
//拿到列的名称
String columnName = rsmd.getColumnName(i+1);
//由于列的名称和bean字段的类型和名称一致,所以可以使用反射去封装
//获得bean中相应的字段
Field declaredField = clazz.getDeclaredField(columnName);
//打开访问权限
declaredField.setAccessible(true);
declaredField.set(bean, value);
}
}
return bean;
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
throw new MyRuntimeException(e);
}
}
}
- BeanListHandler.java
/*
* 用于返回满足多个处理器封装的实现类.
*
* 规定:你需要将封装数据到哪个javaBean上,你的
*
*/
public class BeanListHandler implements ResuletSetHandler {
private Class clazz;
public BeanListHandler(Class clazz) {
// TODO Auto-generated constructor stub
this.clazz = clazz;
}
@Override
public Object handle(ResultSet rs) {
List list = new ArrayList();
try {
ResultSetMetaData rsmd = rs.getMetaData();
while(rs.next()) {
//目标要封装的bean
Object bean = clazz.newInstance();
int columnCount = rsmd.getColumnCount();
for (int i = 0; i < columnCount; i++) {
//拿到当前i ,这列的值
Object value = rs.getObject(i+1);
//拿到列的名称
String columnName = rsmd.getColumnName(i+1);
//由于列的名称和bean字段的类型和名称一致,所以可以使用反射去封装
//获得bean中相应的字段
Field declaredField = clazz.getDeclaredField(columnName);
//打开访问权限
declaredField.setAccessible(true);
declaredField.set(bean, value);
}
list.add(bean);
}
return list;
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
throw new MyRuntimeException(e);
}
}
}
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