genericcomparator.java

利用java反射机制

package org.julp;

import java.lang.Class;
import java.lang.reflect.Method;
import java.io.Serializable;
import java.util.Comparator;
import java.lang.reflect.InvocationTargetException;

public class GenericComparator implements Comparator, Serializable, Cloneable {
    
    protected String methodName = null;
    protected Class[] parmClass = null;    
    protected Object[] parms = null;          
    protected boolean reverse = false;          
       
    public GenericComparator() {
    }
    
    public GenericComparator(String methodName) {
        this.methodName = methodName; 
        this.parmClass = new Class[0];                
    }  
    
    public GenericComparator(String methodName, boolean reverse) {
        this.methodName = methodName; 
        this.parmClass = new Class[0]; 
        this.reverse = reverse;
    }  
    
    public GenericComparator(String methodName, Object[] parms) {
        this.methodName = methodName;
        this.parmClass = new Class[parms.length];        
        this.parms = parms;
        for (int i = 0; i < parms.length; i++){
            this.parmClass[i] = parms.getClass();
        }
    }  
    
    public GenericComparator(String methodName, Object[] parms, boolean reverse) {
        this.methodName = methodName;
        this.parmClass = new Class[parms.length];        
        this.reverse = reverse;
        this.parms = parms;
        for (int i = 0; i < parms.length; i++){
            this.parmClass[i] = parms.getClass();
        }
    }          
    
    public int compare(Object o1, Object o2) {
        Method objMethod = null;
        Object object1 = null;
        Object object2 = null;
        if(!(o1.getClass().isInstance(o2))) {
            throw new ClassCastException("Classes do not match " +
            o1.getClass().getName() + " : " + o2.getClass().getName());
        }
        try {
            objMethod = o1.getClass().getMethod(methodName, parmClass);
        }catch(NoSuchMethodException e) {
            throw new RuntimeException("Method name: " + this.methodName +
            " not found in class " + o1.getClass().getName());
        }
        try {
            object1 = objMethod.invoke(o1, parms);
            object2 = objMethod.invoke(o2, parms);
        }catch(IllegalAccessException e1) {
            throw new RuntimeException("Access denied to method " +
                this.methodName + " in class " + o1.getClass().getName());
        }catch(InvocationTargetException e2) {
            throw new RuntimeException(this.methodName + " in class "+
            o1.getClass().getName() + " threw an exception: " + e2.getMessage());
        }
        
        if (object1 == null || object2 == null){
           return -1; 
        }
        if (isReverse()){
            return - ((Comparable)object1).compareTo(object2);
        }else{
            return ((Comparable)object1).compareTo(object2);
        }        
    }
    
    /** Getter for property methodName.
     * @return Value of property methodName.
     *
     */
    public java.lang.String getMethodName() {
        return methodName;
    }
    
    /** Setter for property methodName.
     * @param methodName New value of property methodName.
     *
     */
    public void setMethodName(java.lang.String methodName) {
        this.methodName = methodName;
    }
    
    /** Getter for property parmClass.
     * @return Value of property parmClass.
     *
     */
    public java.lang.Class[] getParmClass() {
        return this.parmClass;
    }
    
    /** Setter for property parmClass.
     * @param parmClass New value of property parmClass.
     *
     */
    public void setParmClass(java.lang.Class[] parmClass) {
        this.parmClass = parmClass;
    }
    
    /** Getter for property parms.
     * @return Value of property parms.
     *
     */
    public java.lang.Object[] getParms() {
        return this.parms;
    }
    
    /** Setter for property parms.
     * @param parms New value of property parms.
     *
     */
    public void setParms(java.lang.Object[] parms) {
        this.parms = parms;
    }
    
    /** Getter for property reverse.
     * @return Value of property reverse.
     *
     */
    public boolean isReverse() {
        return reverse;
    }
    
    /** Setter for property reverse.
     * @param reverse New value of property reverse.
     *
     */
    public void setReverse(boolean reverse) {
        this.reverse = reverse;
    }
    
}