java反射原理制作对象打印工具

主要运用java反射原理，格式化输出java对象属性值，特别是list 和map。

MyTestUtil.java

package utils;

import java.lang.reflect.Field;
import java.text.SimpleDateFormat;
import java.util.Arrays;
import java.util.Collection;
import java.util.Date;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;

/**
 * 这个类是方便控制台输出object，主要应用java反射机制。 因为考虑到使用性和美观性，没有使用无限递归。
 * 而是在toStr方法中加入一个boolean recursion ，是否递归。
 * 当然我们也可以将boolean recursion换成int recursion，控制递归次数。
 * 其实就我使用经验来看，复杂数据toString，用json工具转化成json输出是一个不错的方式。
  //这是我用的方式，boolean recursion是否递归
  public static int add(int i,boolean recursion){
    sum+=i;
    if(recursion)
      add(i, false);
    return sum;
  }
  //也可以这样，int recursion表示递归次数
  public static int add(int i,int recursion){
    sum+=i;
    if(recursion>0){
      recursion--;
      add(i, recursion);
    }
    return sum;
  }
 *
 *
 * @author klguang
 *
 */

public class MyTestUtil {
  static final String SPLIT_LINE = "=";// 分割线
  static final String MY_SIGN = "KLG_print";//默認標記
  private static String DATE_FORMAT = "yyyy-MM-dd HH:mm:ss";

  /**
   * 将集合类型toSring方法
   * @param object
   * @param recursion
   *      是否递归
   * @return
   */
  private static String collectionToStr(Object object, boolean recursion) {
    if (object == null)
      return "null";
    Object[] a = null;
    // 将集合类型转换成数组类型
    if (isArrayType(object))
      a = (Object[]) object;
    else
      a = ((Collection) object).toArray();
    if (isSimpleArr(a) || !recursion)
      return Arrays.toString(a);
    else
      return complexArrToStr(a);
  }

  /**
   * Arrays有toString方法，但是对象内容太多，在一行显示 还有就是没有显示index信息
   */
  private static String complexArrToStr(Object[] a) {
    if (a == null)
      return "null";

    int iMax = a.length - 1;
    if (iMax == -1)
      return "[]";

    StringBuilder b = new StringBuilder();
    for (int i = 0;; i++) {
      String value = objToStr(a[i], false);
      b.append("[" + i + "]" + " -> " + value);
      if (i == iMax)
        return b.toString();
      b.append(", \r\n");
    }
  }

  /**
   * map类型toString方法
   *
   * @param map
   * @param recursion
   *      是否递归
   * @return
   */
  private static String mapToStr(Map<String, Object> map, boolean recursion) {
    if (map == null)
      return "null";
    if (isSimpleMap(map) || !recursion)
      return simpleMapToStr(map);
    else
      return complexMapToStr(map, true);
  }

  /**
   * map的value是简单类型的，复制Map.toString，我给它加了换行10个换行
   *
   * @param map
   * @return
   */
  private static String simpleMapToStr(Map map) {
    Iterator<Entry<String, Object>> i = map.entrySet().iterator();
    if (!i.hasNext())
      return "{}";

    StringBuilder sb = new StringBuilder();
    sb.append('{');
    for (int t = 1;; t++) {
      Entry<String, Object> e = i.next();
      sb.append(e.getKey()).append(" = ").append(e.getValue());
      if (!i.hasNext())
        return sb.append('}').toString();
      sb.append(',').append(' ');
      if (t % 10 == 0 && t != 0)
        sb.append("\r\n ");
    }
  }

  private static String complexMapToStr(Map map, boolean recursion) {
    Iterator<Entry<String, Object>> i = map.entrySet().iterator();
    if (!i.hasNext())
      return "{}";
    StringBuilder sb = new StringBuilder();
    sb.append("{\r\n");
    for (int t = 1;; t++) {
      Entry<String, Object> e = i.next();
      String key = String.valueOf(e.getKey());
      Object value = e.getValue();
      sb.append(indent(2," ")).append(key).append(" = ");
      if (isSimpleType(value) || !recursion)
        sb.append(String.valueOf(value));
      else
        sb.append(objToStr(value, false));
      if (!i.hasNext())
        return sb.append("\r\n}").toString();
      sb.append(',').append("\r\n");
    }
  }

  /**
   *
   *
   * @param object
   * @param recursion
   *      是否要递归
   * @return
   */
  private static String beanToStr(Object object, boolean recursion) {
    if (object == null)
      return "null";
    Class clazz = object.getClass();
    StringBuilder sb = new StringBuilder();
    //返回源代码中给出的底层类的简称
    sb.append(clazz.getSimpleName()).append("[");
    Field[] fields = sortFieldByType(clazz.getDeclaredFields());
    int iMax = fields.length - 1;
    if (iMax == -1)
      return sb.append("]").toString();
    for (int i = 0;; i++) {
      Field field = fields[i];
      field.setAccessible(true);// 设置些属性是可以访问的
      String name = field.getName();// 取得field的名称
      if (name.equals("serialVersionUID"))
        continue;
      try {
        Object value = field.get(object);// 得到此属性的值
        if (isSimpleType(value) || !recursion)
          sb.append(name + " = " + String.valueOf(value));
        else
          sb.append("\r\n" + indent(clazz.getSimpleName().length() + 2," ")
              + objToStr(value, false) + "\r\n");
      } catch (Exception e) {
        e.printStackTrace();
      }
      if (i == iMax)
        return sb.append("]").toString();
      sb.append(",");
    }
  }

  private static String indent(int length,String sign) {
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < length; i++) {
      sb.append(sign);
    }
    return sb.toString();
  }

  private static boolean isSimpleType(Object obj) {
    if (obj == null)
      return true;
    else {
      Class objectClass = obj.getClass();
      return isSimpleType(objectClass);
    }
  }

  /**
   *
   * @param objectClass
   *      用obj.getClass()取得
   * @return
   */
  private static boolean isSimpleType(Class objectClass) {
    if (objectClass == boolean.class || objectClass == Boolean.class
        || objectClass == short.class || objectClass == Short.class
        || objectClass == byte.class || objectClass == Byte.class
        || objectClass == int.class || objectClass == Integer.class
        || objectClass == long.class || objectClass == Long.class
        || objectClass == float.class || objectClass == Float.class
        || objectClass == char.class || objectClass == Character.class
        || objectClass == double.class || objectClass == Double.class
        || objectClass == String.class) {
      return true;
    } else {
      return false;
    }
  }

  /**
   * Method isCollectionType
   *
   * @param obj
   *      Object
   * @return boolean
   */
  private static boolean isCollectionType(Object obj) {
    if (obj == null)
      return false;
    return (obj.getClass().isArray() || (obj instanceof Collection));
  }

  private static boolean isArrayType(Object obj) {
    if (obj == null)
      return false;
    return (obj.getClass().isArray());
  }

  private static boolean isMapType(Object obj) {
    if (obj == null)
      return false;
    return (obj instanceof Map);
  }

  private static boolean isDateType(Object obj){
    if(obj==null)
      return false;
    return (obj instanceof Date);
  }

  private static boolean isBeanType(Object obj) {
    if (isSimpleType(obj) || isCollectionType(obj) || isMapType(obj))
      return false;
    else
      return true;
  }

  private static boolean isSimpleArr(Object[] a) {
    if (a == null || a.length < 1)
      return true;
    boolean flag = true;
    for (Object o : a) {
      if (!isSimpleType(o)) {
        flag = false;
        break;
      }
    }
    return flag;
  }

  private static boolean isSimpleMap(Map map) {
    if (map == null)
      return true;
    Iterator<Entry<String, Object>> i = map.entrySet().iterator();
    boolean flag = true;
    while (i.hasNext()) {
      Entry<String, Object> e = i.next();
      if (!isSimpleType(e.getValue())) {
        flag = false;
        break;
      }
    }
    return flag;
  }

  /***
   * 将简单类型排在前面
   * @param fields
   * @return
   */

  public static Field[] sortFieldByType(Field[] fields) {
    for (int i = 0; i < fields.length; i++) {
      if (isSimpleType(fields[i].getType()))
        continue;// fields[i]是简单类型不管
      // fields[i]是复杂类型
      // int j = i+1，从fields[i]之后开始比较
      for (int j = i + 1; j < fields.length; j++) {
        Field fieldTmp = null;
        if (isSimpleType(fields[j].getType())) {// 与后面的第一个简单类型交互
          fieldTmp = fields[i];
          fields[i] = fields[j];
          fields[j] = fieldTmp;
          break; // 后面的循环，是没有意义de
        }
      }
    }
    return fields;
  }

  /**
   * 这个方法是递归方法，并且并多个地方调用，考虑到循环引用和显示格式， boolean recursion取得确保递归可以被终止。
   *
   * @param object
   * @param recursion
   *      是否需要更深一层显示
   * @return
   */
  private static String objToStr(Object object, boolean recursion) {
    if (object == null)
      return "null";
    object.toString();
    if(isDateType(object))
      return new SimpleDateFormat(DATE_FORMAT).format((Date)object);
    else if (isBeanType(object))
      return beanToStr(object, recursion);
    else if (isCollectionType(object))
      return collectionToStr(object, recursion);
    else if (isMapType(object))
      return mapToStr((Map) object, recursion);
    else
      return String.valueOf(object);
  }

  public static String objToStr(Object obj) {
    return objToStr(obj, true);
  }

  private static void print(Object obj,String sign,String content) {
    String begin=indent(15, SPLIT_LINE) + " " +obj.getClass().getSimpleName()
      + " >> " + sign + " " + indent(10, SPLIT_LINE);
    int length=(begin.length()-sign.length()-5)/2;

    String end=indent(length, SPLIT_LINE)+ " " + sign + " " + indent(length, SPLIT_LINE);
    System.out.println(begin+"\r\n"+content+"\r\n"+end);

  }
  public static void print(Object obj){
    print(obj,MY_SIGN,objToStr(obj));
  }
  public static void printWithSign(String sign, Object obj) {
    print(obj, sign,objToStr(obj));
  }
}

不过呢上面代码太繁琐了，没有考虑多种类型嵌套的问题。
数组类型强转会报ClassCastException 。
平常打日志就用log4j写个工具方法 比上面这个清晰明了多了。

public static void debug(String message,Object o){
int count=0;
if(o==null){
LOGGER.debug(chain(message,": null"));
return;
}
if(o.getClass().isArray()){
for(int i=0,len=Array.getLength(o);i<len;i++){
debug(chain(message,"-[",i,"]"),Array.get(o, i));
}
}else if(o instanceof Map){
Entry<?,?> e;
for(Iterator<?> it=((Map<?,?>)o).entrySet().iterator();it.hasNext();){
e=(Entry<?,?>) it.next();
debug(chain(message,"-[K:",e.getKey(),"]"),e.getValue());
}
}else if(o instanceof Iterable){
for(Iterator<?> it=((Iterable<?>) o).iterator();it.hasNext();){
count++;
debug(chain(message,"-[",count,"]"),it.next());
}
}else{
LOGGER.debug(chain(message,":",o));
}
}