轻量级JDBC工具类
加载Driver
旧的代码采用Class.forName(driverClassName)加载，实际的Driver注册存在于每个Driver实现的静态初始化块
这里实现的是一种显式的加载，JDBC4以后可以自动加载，无需调用
DbUtils.java1
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| public static boolean loadDriver(String driverClassName) {
return loadDriver(DbUtils.class.getClassLoader(), driverClassName);
}
public static boolean loadDriver(ClassLoader classLoader, String driverClassName) {
try {
Class<?> loadedClass = classLoader.loadClass(driverClassName);
if (!Driver.class.isAssignableFrom(loadedClass)) {
return false;
}
@SuppressWarnings("unchecked")
Class<Driver> driverClass = (Class<Driver>) loadedClass;
Constructor<Driver> driverConstructor = driverClass.getConstructor();
boolean isConstructorAccessible = driverConstructor.isAccessible();
if (!isConstructorAccessible) {
driverConstructor.setAccessible(true);
}
try {
Driver driver = driverConstructor.newInstance();
DriverManager.registerDriver(new DriverProxy(driver));
} finally {
driverConstructor.setAccessible(isConstructorAccessible);
}
return true;
} catch (RuntimeException e) {
return false;
} catch (Exception e) {
return false;
}
}
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关闭资源
关闭全套，注意顺序，先关ResultSet,再关Statement,最后关Connection
DbUtils.java1
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| public static void closeQuietly(Connection conn, Statement stmt,
ResultSet rs) {
try {
closeQuietly(rs);
} finally {
try {
closeQuietly(stmt);
} finally {
closeQuietly(conn);
}
}
}
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静默的关闭就是外包一层try-catch,忽略任何Exception
DbUtils.java1
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| public static void close(Connection conn) throws SQLException {
if (conn != null) {
conn.close();
}
}
public static void closeQuietly(Connection conn) {
try {
close(conn);
} catch (SQLException e) {
}
}
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关闭连接前还可以选择事务提交或者回滚
DbUtils.java1
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| public static void rollbackAndClose(Connection conn) throws SQLException {
if (conn != null) {
try {
conn.rollback();
} finally {
conn.close();
}
}
}
public static void commitAndClose(Connection conn) throws SQLException {
if (conn != null) {
try {
conn.commit();
} finally {
conn.close();
}
}
}
|
ResultSet增强–Null处理功能
直接通过ResultSet获取值并不能区分null值
比如rs.getInt(1),如果数据库里存了null,会返回int默认值0,这样就不知道数据库原本存了0还是null
如果要判断的话需要调用rs.wasNull()，返回上次读取是否是null值
SqlNullCheckedResultSet可以替换每个get方法的默认值成指定值
采用Java代理实现,内置各种类型的nullMethod,rs.wasNull()判断遇到null就返回相应方法进行处理
SqlNullCheckedResultSet.java1
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| public class SqlNullCheckedResultSet implements InvocationHandler {
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
Object result = method.invoke(this.rs, args);
Method nullMethod = nullMethods.get(method.getName());
return (nullMethod != null && this.rs.wasNull())
? nullMethod.invoke(this, (Object[]) null) : result;
}
}
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调用方式，包装后进行配置，创建代理对象
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| SqlNullCheckedResultSet wrapper = new SqlNullCheckedResultSet(rs);
wrapper.setNullString("---N/A---");
wrapper.setNullInt(-999);
rs = ProxyFactory.instance().createResultSet(wrapper);
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ResultSet增强–自动trim
如果采用定长存储，那么数据库会自动加空格
StringTrimmedResultSet同样采用代理，对字符串类型数据自动进行trim
StringTrimmedResultSet.java1
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| public class StringTrimmedResultSet implements InvocationHandler {
private static final ProxyFactory factory = ProxyFactory.instance();
public static ResultSet wrap(ResultSet rs) {
return factory.createResultSet(new StringTrimmedResultSet(rs));
}
private final ResultSet rs;
public StringTrimmedResultSet(ResultSet rs) {
super();
this.rs = rs;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
Object result = method.invoke(this.rs, args);
if ((method.getName().equals("getObject")
|| method.getName().equals("getString"))
&& result instanceof String) {
result = ((String) result).trim();
}
return result;
}
}
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因为无需配置，调用方式比较简单,直接包装就好
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| rs = StringTrimmedResultSet.wrap(rs);
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