如何在Java反射中向方法传递多个参数

Question

嗨，我正在使用反射来实现一些东西。我已经给出了类名，类的方法名和参数值，需要传递给该方法在一个文件(采取任何文件。不是约束)。我需要用参数调用那个方法。这些方法不返回任何东西。在这个类中有一个庞大的方法列表，每个方法的参数列表都是不同的。

E。旅客:method1(String, String, int, boolean)method1(String, int, boolean)和i同样有不同的排列和组合。那么我如何才能做到这一点呢?我试过用不同的开关子句硬编码，但这是一个真正的开销和风险的事情来维护。我们能动态地做这件事吗，比如动态地从文件中读取方法名和它的参数并调用它。任何小的代码片段都会有帮助。TIA。

Answer 1

大家好，我已经找到解决上述问题的方法了。下面是示例代码片段:

package reflections;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
public class ReflectionTest {
    public void method1(String str, int number) {
        System.out.println(str + number);
    }
    public void method1(String str) {
        System.out.println(str);
    }
    public void method1() {
        System.out.println("helloworld");
    }
    public static void main(String[] args) throws ClassNotFoundException,
            InstantiationException, IllegalAccessException,
            NoSuchMethodException, SecurityException, IllegalArgumentException,
            InvocationTargetException {
        // Step 1) Make an object array and store the parameters that you wish
        // to pass it.
        Object[] obj = {};// for method1()
        // Object[] obj={"hello"}; for method1(String str)
        // Object[] obj={"hello",1}; for method1(String str,int number)
        // Step 2) Create a class array which will hold the signature of the
        // method being called.
        Class<?> params[] = new Class[obj.length];
        for (int i = 0; i < obj.length; i++) {
            if (obj[i] instanceof Integer) {
                params[i] = Integer.TYPE;
            } else if (obj[i] instanceof String) {
                params[i] = String.class;
            }
            // you can do additional checks for other data types if you want.
        }
        String methoName = "method1"; // methodname to be invoked
        String className = "reflections.ReflectionTest";// Class name
        Class<?> cls = Class.forName(className);
        Object _instance = cls.newInstance();
        Method myMethod = cls.getDeclaredMethod(methoName, params);
        myMethod.invoke(_instance, obj);
    }
}

Answer 2

public class ReflectionSample
{
    private Object mString = null;
    private int mValue;
    public ReflectionSample()
    {
    }
    public ReflectionSample(int oValue)
    {
        mValue = oValue;
    }
    public ReflectionSample(String oString)
    {
        mString = oString;
    }
    public ReflectionSample(String oString, int oValue)
    {
        setValues(oString, oValue);
    }
    public void setValues(String oString, int oValue)
    {
        mString = oString;
        mValue = oValue;
    }
    public String toString()
    {
        return ""+mString+":"+mValue;
    }
    public void run()
    {
        String oInput = "Teststring";
        Class<?> cls;
        String clsname = "main.ReflectionSample";
        Object rs = null;   // ReflectionSample
        Object rsc = null;
        System.out.println(this.getClass().getName());
        try
        {
            System.out.println(clsname);
            cls = Class.forName(clsname);
            if(cls == null)
            {
                System.err.println(clsname + " doesn't exist");
                return;
            }
            // Look for a constructor which has a single string
            Constructor<?> ct = null;
            Class<?>[] param_types = new Class<?>[1];
            Object[] arguments = new Object[1];
            param_types[0] = String.class;
            // get the string constructor
            ct = cls.getConstructor(param_types);
            // We only have one object
            arguments = new Object[1];
            arguments[0] = oInput;
            // Instantiate the object with passed in argument.
            rs = ct.newInstance(arguments);
            System.out.println("String constructor sample: "+rs);
            // Instantiate with default constructor
            param_types = new Class<?>[0];
            arguments = new Object[0];
            ct = cls.getConstructor(param_types);
            rs = ct.newInstance(arguments);
            rsc = rs; // Keep it for later, to lazy to call it again
            System.out.println("Default constructor sample: "+rs);
            // Instantiate with string and int constructor
            param_types = new Class<?>[2];
            arguments = new Object[2];
            // Must be in the same order as the params I think
            param_types[0] = String.class;
            param_types[1] = Integer.TYPE;      // <-- Its a primitive so use TYPE not Class
            arguments[0] = oInput;
            arguments[1] = new Integer(1);
            ct = cls.getConstructor(param_types);
            rs = ct.newInstance(arguments);
            System.out.println("String plus int constructor sample: "+rs);
            // call the setValues method
            param_types[0] = String.class;
            param_types[1] = Integer.TYPE;      // <-- Its a primitive so use TYPE not Class
            arguments[0] = oInput;
            arguments[1] = 1;
            System.out.println("setValues invocation before: "+rsc);
            Method m = cls.getMethod("setValues", param_types);
            m.invoke(rsc, arguments);
            System.out.println("setValues invocation after: "+rsc);
            // An alternative method to pass the parameters
            m = cls.getMethod("setValues", String.class, Integer.TYPE);
            m.invoke(rsc, oInput+"x", 2);
            System.out.println("setValues invocation after: "+rsc);
        }
        catch(Throwable e)
        {
            System.err.println(e.getLocalizedMessage());
        }
    }
}

输出:

main.ReflectionSample
main.ReflectionSample
String constructor sample: Teststring:0
Default constructor sample: null:0
String plus int constructor sample: Teststring:1
setValues invocation before: null:0
setValues invocation after: Teststring:1

希望对你有帮助。

我不知道这是否是Java中的新功能，但我已经看到您现在可以使用参数调用，而不是使用数组，这可能使您的代码更好地阅读(这是另一种方式)。如果您需要可变数量的参数，并且事先不知道有多少个参数，那么分配数组肯定是有效的，并且应该是向后兼容的。

Answer 3

一个简单的解决方案是创建一个Class，其中包含需要传递的参数:

public class ObjectArguments {
  private PrintWriter out;
  private String productId;
  private int action;
  public ObjectArguments(PrintWriter out, String productId, int action) {
    this.out = out;
    this.productId = productId;
    this.action = action;
  }
  public PrintWriter getOut() {
    return out;
  }
  public String getProductId() {
    return productId;
  }
  public int getAction() {
    return action;
  }
}

假设你想用一个名为bar的方法调用一个类Foo。
那么就这样做。

PrintWriter out = null;
String productId = null;
int action = 0;
Class[] paramArguments = new Class[1];  
paramArguments[0] = ObjectArguments.class;  
ObjectArguments newObj = new ObjectArguments(out,productId,action);
Class cls = Class.forName("Foo");
Object obj = cls.newInstance();
Method method = cls.getDeclaredMethod("bar", paramArguments);
method.invoke(obj, newObj);

Answer 4

对于两个int形参，示例如下，类似地，其他数据类型形参也可以调用

Method method=new Test1().getClass().getMethod(x, new Class[] {int.class,int.class});

我们可以调用一个需要三个参数int,int,string的方法，如下所示:

Method method=new Test1().getClass().getMethod(x, new Class[] {int.class,int.class, String.class});