package com.ycd.reflect;
public class Person {
public String name;
public int age;
public Person() {
}
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public String show(){
return "name:"+name+", age :"+age;
}
}
package com.ycd.reflect;
public class Student extends Person{
public String className;
private String address;
public Student(){
super();
}
private Student(String name,int age,String className){
super(name,age);
this.className= className;
}
public Student(String name,int age,String className,String address){
super(name,age);
this.className = className;
this.address = address;
}
public String getClassName() {
return className;
}
public void setClassName(String className) {
this.className = className;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
private void add(int a,int b){
System.out.println(a+b);
}
@Override
public String toString() {
return "Student{" +
"className='" + className + '\'' +
", address='" + address + '\'' +
", name='" + name + '\'' +
", age=" + age +
'}';
}
}
public class ClassAPI {
public static void main(String[] args) throws Exception{
Class<?> clazz = Class.forName("com.ycd.reflect.Student");
//获取成员变量,包括子类及父类，同时只能包含公共的方法
Field[] fields = clazz.getFields();
for (Field field : fields) {
System.out.println(field);
System.out.println(field.getName());
System.out.println(field.getType());
System.out.println(field.getModifiers());
System.out.println("-----");
}
System.out.println("1=======================1");
//此方法返回的是当前类的所有属性，不仅仅局限于公共访问修饰符，所有的访问修饰符都可以拿到
Field[] declaredFields = clazz.getDeclaredFields();
for (Field declaredField : declaredFields) {
System.out.println(declaredField.getName());
}
System.out.println("2========================2");
//反射在一定程度上破坏了封装性，需要合理使用
Field address = clazz.getDeclaredField("address");
//设置该属性是否能被访问，true表示能被访问，破坏了封装性
address.setAccessible(true);
System.out.println(address.getName());
Object o = clazz.newInstance();
address.set(o,"北京市");
System.out.println(((Student)o).getAddress());
System.out.println("3========================3");
//获取该对象的普通方法,包含的方法范围是当前对象及父类对象的所有公共方法
Method[] methods = clazz.getMethods();
for (Method method : methods) {
System.out.println(method.getName());
}
System.out.println("4========================4");
//获取当前类中所有的方法，无论什么访问修饰符
Method[] declaredMethods = clazz.getDeclaredMethods();
for (Method declaredMethod : declaredMethods) {
System.out.println(declaredMethod.getName());
}
System.out.println("5========================5");
Method add = clazz.getDeclaredMethod("add", int.class, int.class);
add.setAccessible(true);
Object o1 = clazz.newInstance();
add.invoke(o1,123,123);
System.out.println("6========================6");
//获取对象的所有构造方法，只能获取公有的改造方法
Constructor<?>[] constructors = clazz.getConstructors();
for (Constructor<?> constructor : constructors) {
System.out.println(constructor.getName());
}
System.out.println("7========================7");
//获取所有的构造方法，无论是私有还是公有
Constructor<?>[] declaredConstructors = clazz.getDeclaredConstructors();
for (Constructor<?> declaredConstructor : declaredConstructors) {
System.out.println(declaredConstructor.getName());
}
//如何调用私有的构造方法呢？
Constructor<?> declaredConstructor = clazz.getDeclaredConstructor(String.class, int.class, String.class);
declaredConstructor.setAccessible(true);
Student o2 = (Student)declaredConstructor.newInstance("msb", 23, "java");
System.out.println(o2);
}
}
输出：
public java.lang.String com.ycd.reflect.Student.className
className
class java.lang.String
1
-----
public java.lang.String com.ycd.reflect.Person.name
name
class java.lang.String
1
-----
public int com.ycd.reflect.Person.age
age
int
1
-----
1=======================1
className
address
2========================2
address
北京市
3========================3
toString
getAddress
getClassName
setClassName
setAddress
show
wait
wait
wait
equals
hashCode
getClass
notify
notifyAll
4========================4
add
toString
getAddress
getClassName
setClassName
setAddress
5========================5
246
6========================6
com.ycd.reflect.Student
com.ycd.reflect.Student
7========================7
com.ycd.reflect.Student
com.ycd.reflect.Student
com.ycd.reflect.Student
Student{className='java', address='null', name='msb', age=23}
下面利用反射，实现了查询sql操作的应用。
/*
* 要查询N张表的数据，但是不想写N多的方法，能否写一个方法完成所有表的查询工作
*
* */
public class BaseDaoImpl {
/**
* 统一的查询表的方法
* @param sql 不同的sql语句
* @param params sql语句的参数
* @param clazz sql语句查询返回的对象
* @return
*/
public List getRows(String sql,Object[] params,Class clazz){
List list = new ArrayList();
Connection connection = null;
PreparedStatement pstmt = null;
ResultSet resultSet = null;
try {
//建立连接
connection = DBUtil.getConnection();
//创建pstmt对象
pstmt = connection.prepareStatement(sql);
//给sql语句填充参数
if(params!=null){
for(int i = 0;i<params.length;i++){
pstmt.setObject(i+1,params[i]);
}
}
//开始执行查询操作,resultset中有返回的结果，需要讲返回的结果放置到不同的对象中
resultSet = pstmt.executeQuery();
//获取结果集合的元数据对象
ResultSetMetaData metaData = resultSet.getMetaData();
//判断查询到的每一行记录中包含多少个列
int columnCount = metaData.getColumnCount();
//循环遍历resultset
while(resultSet.next()){
//创建放置具体结果属性的对象
Object obj = clazz.newInstance();
for(int i= 0;i<columnCount;i++){
//从结果集合中获取单一列的值
Object objValue = resultSet.getObject(i+1);
//获取列的名称
String columnName = metaData.getColumnName(i+1).toLowerCase();
//获取类中的属性
Field declaredField = clazz.getDeclaredField(columnName);
//获取类中属性对应的set方法
Method method = clazz.getMethod(getSetName(columnName),declaredField.getType());
if(objValue instanceof Number){
Number number = (Number) objValue;
String fname = declaredField.getType().getName();
if("int".equals(fname)||"java.lang.Integer".equals(fname)){
method.invoke(obj,number.intValue());
}else if("byte".equals(fname)||"java.lang.Byte".equals(fname)){
method.invoke(obj,number.byteValue());
}else if("short".equals(fname)||"java.lang.Short".equals(fname)){
method.invoke(obj,number.shortValue());
}else if("long".equals(fname)||"java.lang.Long".equals(fname)){
method.invoke(obj,number.longValue());
}else if("float".equals(fname)||"java.lang.Float".equals(fname)){
method.invoke(obj,number.floatValue());
}else if("double".equals(fname)||"java.lang.Double".equals(fname)){
method.invoke(obj,number.doubleValue());
}
}else{
method.invoke(obj,objValue);
}
}
list.add(obj);
}
} catch (Exception e) {
e.printStackTrace();
}finally {
DBUtil.closeConnection(connection,pstmt,resultSet);
}
return list;
}
public String getSetName(String name){
return "set"+name.substring(0,1).toUpperCase()+name.substring(1);
}
public static void main(String[] args) {
BaseDaoImpl baseDao = new BaseDaoImpl();
// List rows = baseDao.getRows("select empno,ename,sal,deptno from emp where deptno =?", new Object[]{10}, Emp.class);
// for(Iterator it = rows.iterator();it.hasNext();){
// Emp emp = (Emp) it.next();
// System.out.println(emp);
// }
List rows = baseDao.getRows("select deptno,dname,loc from dept", new Object[]{}, Dept.class);
for(Iterator it = rows.iterator();it.hasNext();){
Dept dept = (Dept) it.next();
System.out.println(dept);
}
}
}
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