method = clazz.getDeclaredMethod(methodName); java 后端 method.invoke调用方法如何传参
时间: 2024-09-28 14:05:56 浏览: 37
`method.invoke()` 是 Java 中用于动态调用对象方法的一个方法,它通常与反射(Reflection)一起使用。当你通过 `getDeclaredMethod()` 获取到一个方法对象后,你可以使用这个方法来在特定的对象上调用该方法。
传参的过程如下:
```java
Object obj = ...; // 要操作的对象
Object[] args = {arg1, arg2, ...}; // 方法需要的参数列表
// 确保方法可以接受提供的参数
if (method.getParameterCount() == args.length) {
try {
method.invoke(obj, args); // 使用obj作为目标对象,并将args数组传入
} catch (IllegalAccessException | IllegalArgumentException | InvocationTargetException e) {
e.printStackTrace(); // 处理可能出现的异常
}
} else {
System.out.println("参数数量不匹配!");
}
```
这里,`getParameterCount()` 用于获取方法需要的参数个数,`invoke()` 方法会尝试将 `args` 数组中的值依次对应地传递给方法。如果存在权限问题、参数类型错误或者方法抛出异常,你需要捕获并处理相应的异常。
相关问题
请帮忙检查一下代码中的错误:package com.enmo.mdi.distributedcomputing.distributed; import java.util.function.Function; import java.lang.reflect.*; public class Algorithm { public Algorithm() throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, IllegalAccessException { } private Double sum(Double... args) { Double num = 0.0; for (Double d: args){ num += d; } return num; } private String add(String... args) { StringBuilder str = new StringBuilder(); for (String s: args){ str.append(s); } return str.toString(); } public static Object callMethod(String name, Object... args) throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, IllegalAccessException { Class<?> clazz = Class.forName("com.enmo.mdi.distributedcomputing.distributed.Algorithm"); // 获取方法的Method对象 Method method = clazz.getDeclaredMethod(name, Double.class); method.setAccessible(true); // 调用该方法 return method.invoke(null,args); } public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, IllegalAccessException { // sum Double result = (Double) callMethod("sum", 1,2,3,4,5); System.out.println(result); String result1 = (String) callMethod("add", "1", "2", '3'); System.out.println(result1); } }
代码中的问题是:
1. 在调用callMethod()方法时,传入的参数类型不匹配,应该将数字1,2,3,4,5修改为1.0,2.0,3.0,4.0,5.0,即将整型转换为浮点型。对于字符串"3",应该将其改为字符'3'。
2. 在调用callMethod()方法时,获取方法的Method对象时,应该使用Double[].class和String[].class而不是Double.class和String.class,因为参数是可变的数组。
修改后的代码如下:
```java
package com.enmo.mdi.distributedcomputing.distributed;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
public class Algorithm {
public Algorithm() throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {
}
private Double sum(Double... args) {
Double num = 0.0;
for (Double d: args){
num += d;
}
return num;
}
private String add(String... args) {
StringBuilder str = new StringBuilder();
for (String s: args){
str.append(s);
}
return str.toString();
}
public static Object callMethod(String name, Object... args) throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {
Class<?> clazz = Class.forName("com.enmo.mdi.distributedcomputing.distributed.Algorithm");
// 获取方法的Method对象
Method method = clazz.getDeclaredMethod(name, Double[].class);
method.setAccessible(true);
// 调用该方法
return method.invoke(null, (Object) args);
}
public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {
// sum
Double result = (Double) callMethod("sum", 1.0, 2.0, 3.0, 4.0, 5.0);
System.out.println(result);
String result1 = (String) callMethod("add", "1", "2", "3");
System.out.println(result1);
}
}
```
1. 自定义Person类,并给定一个带参构造, 当Person类的反射对象调用newInstance时会报错,写个例子演示,并说明为什么? 2. 有一个电脑类和手机类都有一个brand属性,在工厂类的静态方法中,传入反射对象及属性值,灵活获取到对应的实体对象,返回的对象中包含属性值 3、配置文件中user.properties中有一组键值对为: key=xx.xx.xx.Person 请加载配置文件后,根据key获取出value,并通过反射机制获取对应的实体对象
1. 代码示例:
```java
public class Person {
private String name;
public Person(String name) {
this.name = name;
}
}
public class Main {
public static void main(String[] args) throws Exception {
Class clazz = Person.class;
Object obj = clazz.newInstance("Tom");
}
}
```
运行上述代码会抛出异常:
```
Exception in thread "main" java.lang.NoSuchMethodException: Person.<init>()
```
原因是在反射调用 `newInstance()` 方法时,会调用该类的无参构造方法来创建对象,但是 `Person` 类中只有一个带参构造方法,没有无参构造方法,所以会报错。
2. 代码示例:
```java
public class Computer {
private String brand;
public void setBrand(String brand) {
this.brand = brand;
}
@Override
public String toString() {
return "Computer{" +
"brand='" + brand + '\'' +
'}';
}
}
public class Phone {
private String brand;
public void setBrand(String brand) {
this.brand = brand;
}
@Override
public String toString() {
return "Phone{" +
"brand='" + brand + '\'' +
'}';
}
}
public class Factory {
public static Object getInstance(Class clazz, String brand) throws Exception {
Object obj = clazz.newInstance();
Field field = clazz.getDeclaredField("brand");
field.setAccessible(true);
field.set(obj, brand);
return obj;
}
}
public class Main {
public static void main(String[] args) throws Exception {
Object computer = Factory.getInstance(Computer.class, "Lenovo");
System.out.println(computer);
Object phone = Factory.getInstance(Phone.class, "Apple");
System.out.println(phone);
}
}
```
3. 代码示例:
```java
public class Person {
private String name;
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Person{" +
"name='" + name + '\'' +
'}';
}
}
public class Main {
public static void main(String[] args) throws Exception {
Properties props = new Properties();
InputStream in = Main.class.getClassLoader().getResourceAsStream("user.properties");
props.load(in);
in.close();
String className = props.getProperty("key");
Class clazz = Class.forName(className);
Object obj = clazz.newInstance();
Method method = clazz.getDeclaredMethod("setName", String.class);
method.invoke(obj, "Tom");
System.out.println(obj);
}
}
```
假设 `user.properties` 文件中的内容如下:
```
key=com.example.Person
```
上述代码会根据 `key` 获取到 `Person` 类的类对象,并通过反射机制创建实例,并调用 `setName()` 方法设置属性值,最后输出实例对象。
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