day40
反射应用
案例
1.万能数组扩容
设置泛型的copyof仅支持引用数据类型,即任意类型,直接new数组不行,利用反射实现扩容;
打印调用toString也进行编写,利用StringBuffer或者StringBiulder进行字符串拼接
public class Test01 {public static void main(String[] args) {//引用数据类型String[] ss = {"小小","大大","奇奇","怪怪","奇男子"};String[] newSS = MyArrays.copyOf(ss, 8);System.out.println(MyArrays.toString(newSS));//基本数据类型int[] is = {1,2,3,4,5};int[] newIS = MyArrays.copyOf(is, 8);System.out.println(MyArrays.toString(newIS));}
}
对前面学习的数组,编写的工具类补充
/*** 史上最牛逼的数组工具类* @author 奇男子* @version 1.0*/
public class MyArrays {/*** 数组的排序* @param a 目标数组*/public static void sort(int[] a){for (int i = 0; i < a.length-1; i++) {for (int j = 0; j < a.length-1-i; j++) {if(a[j] > a[j+1]){int temp = a[j];a[j] = a[j+1];a[j+1] = temp;}}}}/*** 数组的查找,必须先排序,在查找* @param a 目标数组* @param key 需要查找的键* @return 如果搜索的元素包含在数组中就返回元素的下标; 否则,返回(-插入点-1)*/public static int binarySearch(int[] a,int key){int start = 0;int end = a.length-1;while(start <= end){int mid = (start+end)/2;if(key < a[mid]){end = mid-1;}else if(key > a[mid]){start = mid+1;}else{return mid;}}return -start-1;}/*** 拷贝数组* @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;}/*** 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[].classClass<?> 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;}/*** 拷贝区间数组* @param original 目标数组* @param from 开始下标-包含* @param to 结束下标 - 排他* @return 新数组*/public static int[] copyOfRange(int[] original, int from, int to){int newLength = to-from;int[] newArr = new int[newLength];int index = 0;for (int i = from; i < to; i++) {newArr[index++] = original[i];}return newArr;}/*** 替换全部元素* @param a 目标数组* @param val 替换的值*/public static void fill(int[] a, int val){fill(a, 0, a.length, val);}/*** 替换区间元素* @param a 目标数组* @param fromIndex 开始下标 - 包含* @param toIndex 结束下标 - 排他* @param val 替换的值*/public static void fill(int[] a, int fromIndex, int toIndex, int val){for (int i = fromIndex; i < toIndex; i++) {a[i] = val;}}/*** 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.业务与逻辑分离的思想
需求:
用户选择获取数据的方式(本地数据、网络数据)
实现
版本01
版本01:if-else直接实现
public class Test01 {public static void main(String[] args) {Scanner scan = new Scanner(System.in);System.out.println("请选择获取数据的方式:");System.out.println("1-获取本地数据");System.out.println("2-获取网络数据");int num = scan.nextInt();if(num == 1){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();}}}}else if(num == 2){//https://wx2.sinaimg.cn/mw690/e2438f6cly1hoo3qpm7vrj21111jk4mn.jpgSystem.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();}}scan.close();}
}
版本02
版本02:简单分离,优化if-else问题
优化:使用类、接口哪个更好?
注意:
如果就只是固定功能或者说DataSource仅是有抽象方法就用接口更好
如果需要添加新的功能用类更好
public class Test01 {public static void main(String[] args) {Scanner scan = new Scanner(System.in);System.out.println("请选择获取数据的方式:");System.out.println("1-获取本地数据");System.out.println("2-获取网络数据");int num = scan.nextInt();if(num == 1){LocalDataSource dataSource = new LocalDataSource();dataSource.getDataSource();}else if(num == 2){NetworkDataSource dataSource = new NetworkDataSource();dataSource.getDataSource();}scan.close();}
}
数据源
public abstract class DataSource {public abstract void getDataSource();}//获取本地资源的类
public class LocalDataSource extends DataSource{private Scanner scan;public LocalDataSource() {scan = new Scanner(System.in);}@Overridepublic 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
public class NetworkDataSource extends DataSource{private Scanner scan;public NetworkDataSource() {scan = new Scanner(System.in);}@Overridepublic void getDataSource() {//https://wx2.sinaimg.cn/mw690/e2438f6cly1hoo3qpm7vrj21111jk4mn.jpgSystem.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();}}
}
版本03
版本03:在原有基础,新增功能
对菜单和数据源都在数据中心配合配置文件进行初始,可维护性更好
将菜单信息放在配置文件,再取出来存在一个集合里(ps:代码中的数据中心dataSource)
再打印查看展示
本地资源,网络资源路径放在配置文件
初始化数据源的循环获取对象,放在dataSource添加其他功能,即新增功能,更改配置文件
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;}
}
数据中心
//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();} }}
}
配置文件
menuConfig.properties
注意:写进去不是中文显示为正常现象
data=1-\u83B7\u53D6\u672C\u5730\u6570\u636E,2-\u83B7\u53D6\u7F51\u7EDC\u6570\u636E,3-\u83B7\u53D6\u5176\u4ED6\u6570\u636E
dataSourceConfig.properties
data=com.qf.reflex02.LocalDataSource,com.qf.reflex02.NetworkDataSource,com.qf.reflex02.OtherDataSource
数据源
public abstract class DataSource {public abstract void getDataSource();}//获取本地资源的类
public class LocalDataSource extends DataSource{private Scanner scan;public LocalDataSource() {scan = new Scanner(System.in);}@Overridepublic 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
public class NetworkDataSource extends DataSource{private Scanner scan;public NetworkDataSource() {scan = new Scanner(System.in);}@Overridepublic void getDataSource() {//https://wx2.sinaimg.cn/mw690/e2438f6cly1hoo3qpm7vrj21111jk4mn.jpgSystem.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();}}
}//新增功能的类
public class OtherDataSource extends DataSource{@Overridepublic void getDataSource() {System.out.println("获取其他数据");}}
3.操作注解
简单涉及注解开发,没有遵循注解规范就报错,当然这里处理是随便抛的异常
注意:这里为前面反射获取注解信息及实际运用做了补充
工具类里,利用反射,设置权限,获取注解,属性的数据拿到
数据字符串拼接用StringBuilder或者Strinngbuffer
//表
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface TableInfo {String name();
}
//属性
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface FieldInfo {String name();String type();
}
学生类
添加注解
package com.qf.reflex03;@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;public Student() {}public Student(String name, String sex, int age) {this.name = name;this.sex = sex;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getSex() {return sex;}public void setSex(String sex) {this.sex = sex;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}@Overridepublic String toString() {return "Student [name=" + name + ", sex=" + sex + ", age=" + age + "]";}
}
工具类
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;}}
测试类
public class Test01 {public static void main(String[] args) {Student stu = new Student("奇男子", "男", 18);String sql = DBUtil.generateInsertSQL(stu);System.out.println(sql);//INSERT INTO s_student(s_name,s_sex,s_age) VALUES('奇男子','男',18);}
}
总结
1.反射案例 – 万能数组扩展
注意:
1.泛型的使用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DataCenter3.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