Day40
1.反射案例 之 万能数组扩容
java
public class Test01 {
public static void main(String[] args) {
String[] ss = {"小希","小空","小丽","小光","小爱"};
String[] newSS = MyArrays.copyOf(ss, 8);
System.out.println(MyArrays.toString(newSS));
int[] is = {1,2,3,4,5};
int[] newIS = MyArrays.copyOf(is, 8);
System.out.println(MyArrays.toString(newIS));
}
}MyArrays类
java
public class MyArrays {
/**
* 拷贝数组（以前的方法）
* @param original 目标数组
* @param newLength 新数组的长度
* @return 新数组
*/
public static int[] copyOf(int[] original, int newLength){
int copyLength = original.length;
if(copyLength > newLength){
copyLength = newLength;
}
int[] newArr = new int[newLength];
for (int i = 0; i < copyLength; i++) {
newArr[i] = original[i];
}
return newArr;
}
/**
* 反射的方法
* 引用数据类型数组的扩容（不支持基本数据类型）
* @param original
* @param newLength
* @return
*/
public static <T> T[] copyOf(T[] original , int newLength){
int copyLength = original.length;
if(copyLength > newLength){
copyLength = newLength;
}
//获取元素的类型
Class<? extends Object[]> clazz = original.getClass();//String[].class
Class<?> componentType = clazz.getComponentType();//String.clss
//利用反射创建数组
@SuppressWarnings("unchecked")
T[] ts = (T[]) Array.newInstance(componentType, newLength);
//遍历源数组，将数据复制到新数组中
for (int i = 0; i < copyLength; i++) {
//获取源数组的数据
Object element = Array.get(original, i);
//赋值给新数组
Array.set(ts, i, element);
}
return ts;
}
/**
* 将数组转换为字符串
* @param a 目标数组
* @return 转换后的字符串
*/
public static String toString(int[] is) {
StringBuffer sb = new StringBuffer();
sb.append("[");
for (int element : is) {
if(sb.length() != 1){
sb.append(",");
}
sb.append(element);
}
sb.append("]");
return sb.toString();
}
/**
* 将数组转换为字符串
* @param a 目标数组
* @return 转换后的字符串
*/
public static <T> String toString(T[] a){
StringBuffer sb = new StringBuffer();
sb.append("[");
for (int i = 0; i < Array.getLength(a); i++) {
if(sb.length() != 1){
sb.append(",");
}
Object element = Array.get(a, i);
sb.append(element);
}
sb.append("]");
return sb.toString();
}
}2.反射案例 之 业务与逻辑分离 的思想
invoke方法参数的意义
参数一：表示代理对象，一般不用（了解）
参数二：就是方法名，我们可以对方法名进行判断，是增强还是拦截
参数三：调用方法时，传递的参数
需求：用户选择获取数据的方式（本地数据、网络数据）
java
public class Test01 {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
showMenu();
int num = scan.nextInt();
DataSource dataSource = getDataSourceObject(num);
dataSource.getDataSource();
scan.close();
}
public static void showMenu(){
System.out.println("请选择获取数据的方式：");
ArrayList<String> menulist = DataCenter.menuList;
for (String element : menulist) {
System.out.println(element);
}
}
public static DataSource getDataSourceObject(int num){
DataSource dataSource = DataCenter.dataSourceList.get(num-1);
return dataSource;
}
}配置文件
dataSourceConfig.properties
properties
data=com.qf.reflex02.LocalDataSource,com.qf.reflex02.NetworkDataSource,com.qf.reflex02.OtherDataSourcemenuConfig.properties
properties
data=1-\u83B7\u53D6\u672C\u5730\u6570\u636E,2-\u83B7\u53D6\u7F51\u7EDC\u6570\u636E,3-\u83B7\u53D6\u5176\u4ED6\u6570\u636E
java
public abstract class DataSource {
public abstract void getDataSource();
}数据中心类（选择1,2，3，继续第几个操作）
java
//数据中心
public class DataCenter {
public static final ArrayList<String> menuList;
public static final ArrayList<DataSource> dataSourceList;
//初始化菜单数据
static{
menuList = new ArrayList<>();
Properties p = new Properties();
try {
p.load(DataCenter.class.getClassLoader().getResourceAsStream("menuConfig.properties"));
} catch (IOException e) {
e.printStackTrace();
}
String data = p.getProperty("data");
String[] split = data.split(",");
Collections.addAll(menuList, split);
}
//初始化数据源数据
static{
dataSourceList = new ArrayList<>();
Properties p = new Properties();
try {
p.load(DataCenter.class.getClassLoader().getResourceAsStream("dataSourceConfig.properties"));
} catch (IOException e) {
e.printStackTrace();
}
String data = p.getProperty("data");
String[] split = data.split(",");
for (String classPath : split) {
try {
Class<?> clazz = Class.forName(classPath);
DataSource dataSouce = (DataSource) clazz.newInstance();
dataSourceList.add(dataSouce);
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
}
}获取本地资源的类(第一个选择)
java
//获取本地资源的类
public class LocalDataSource extends DataSource{
private Scanner scan;
public LocalDataSource() {
scan = new Scanner(System.in);
}
@Override
public void getDataSource() {
System.out.println("请填写需要拷贝文件的路径：");
String path = scan.next();
File file = new File(path);
BufferedInputStream bis = null;
BufferedOutputStream bos = null;
try {
bis = new BufferedInputStream(new FileInputStream(path));
bos = new BufferedOutputStream(new FileOutputStream(file.getName()));
byte[] bs = new byte[1024];
int len;
while((len=bis.read(bs)) != -1){
bos.write(bs, 0, len);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if(bis != null){
try {
bis.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if(bos != null){
try {
bos.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}获取网络资源的类(第二个选择)
java
//获取网络资源的类
public class NetworkDataSource extends DataSource{
private Scanner scan;
public NetworkDataSource() {
scan = new Scanner(System.in);
}
@Override
public void getDataSource() {
//https://wx2.sinaimg.cn/mw690/e2438f6cly1hoo3qpm7vrj21111jk4mn.jpg
System.out.println("请填写下载图片的网址：");
String path = scan.next();
try {
//创建链接对象
URL url = new URL(path);
//获取连接对象
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
//设置参数
connection.setConnectTimeout(5000);//设置连接超时时间
connection.setReadTimeout(5000);//设置读取数据超时时间
connection.setDoInput(true);//设置是否允许使用输入流
connection.setDoOutput(true);//设置是否允许使用输出流
//获取响应状态码
int code = connection.getResponseCode();
if(code == HttpURLConnection.HTTP_OK){
//文件名
String fileName = path.substring(path.lastIndexOf("/")+1);
BufferedInputStream bis = new BufferedInputStream(connection.getInputStream());
BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(fileName));
byte[] bs = new byte[1024];
int len;
while((len = bis.read(bs)) != -1){
bos.write(bs, 0, len);
}
bis.close();
bos.close();
}else if(code == HttpURLConnection.HTTP_NOT_FOUND){
System.out.println("页面未找到");
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}其他数据(第三个选择)
java
//其他数据
public class OtherDataSource extends DataSource{
@Override
public void getDataSource() {
System.out.println("获取其他数据");
}
}3.反射案例 之 操作注解
利用注解使Student类的属性与数据库表名一致，与mybatis的起别名差不多
java
public class Test01 {
public static void main(String[] args) {
Student stu = new Student("小威", "男", 18);
String sql = DBUtil.generateInsertSQL(stu);
System.out.println(sql);
//INSERT INTO s_student(s_name,s_sex,s_age) VALUES('小威','男',18);
}
}类名注解
java
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface TableInfo {
String name();
}属性注解
java
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface FieldInfo {
String name();
String type();
}Student类
java
@TableInfo(name="s_student")
public class Student {
@FieldInfo(name="s_name",type="varchar")
private String name;
@FieldInfo(name="s_sex",type="varchar")
private String sex;
@FieldInfo(name="s_age",type="int")
private int age;
//有参构造，无参构造，get，set方法省略
}数据库SQL拼接：INSERT INTO s_student(s_name,s_sex,s_age) VALUES('小威','男',18);
java
public class DBUtil {
public static String generateInsertSQL(Object obj){
Class<? extends Object> clazz = obj.getClass();
//获取表名
TableInfo tableInfo = clazz.getAnnotation(TableInfo.class);
if(tableInfo == null){
throw new RuntimeException();
}
String tableName = tableInfo.name();
StringBuffer names = new StringBuffer();
StringBuffer values = new StringBuffer();
//获取属性数据
Field[] fields = clazz.getDeclaredFields();
for (Field field : fields) {
field.setAccessible(true);
FieldInfo fieldInfo = field.getAnnotation(FieldInfo.class);
String name = fieldInfo.name();
String type = fieldInfo.type();
if(names.length() != 0){
names.append(",");
}
names.append(name);
try {
if(values.length() != 0){
values.append(",");
}
Object fieldData = field.get(obj);
if(type.equals("varchar")){
values.append("'");
}
values.append(fieldData);
if(type.equals("varchar")){
values.append("'");
}
} catch (IllegalArgumentException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
String sql = "INSERT INTO " + tableName + "(" + names.toString() + ") VALUES(" + values.toString() + ");";
return sql;
}
}你觉得反射好不好？好，有两个方向
第一个方向：无视修饰符访问类中的内容。但是这种操作在开发中一般不用，都是框架底层来用的。
第二个方向：反射可以跟配置文件结合起来使用，动态的创建对象，动态的调用方法。
总结
1.反射案例 -- 万能数组扩展
注意：
1.泛型的使用
2.利用Array操作数组
2.反射案例 -- 业务与逻辑分离的思想
注意：
1.理解思想
2.灵活使用配置文件
3.理解数据中心DataCenter
3.反射案例 -- 操作注解
注意：
1.理解注解是可以给类、属性、方法提供额外信息