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Java反射应用实例

 2012/1/19 9:12:24  hejiangtao  程序员俱乐部  我要评论(0)
  • 摘要：本文主要通过Java反射应用实例来讲解利用反射方法创建对象(使用默认构造函数和自定义构造函数),访问对应对象的方法(包括带参数的和不带参数的),访问对应对象的域(Field).从这里可以下载到完整的java代码工程:http://download.csdn.net/detail/hejiangtao/4011663很多IOC等框架都使用反射来实现,例如Spring,Hibernate等,Java反射的方式实现的逻辑比普通类逻辑的效率是要差一些的(14至300倍左右)
  • 标签：Java 应用 反射 实例

本文主要通过Java反射应用实例来讲解 利用反射方法创建对象(使用默认构造函数和自定义构造函数) ,访问对应对象的方法(包括带参数的和不带参数的),访问对应对象的域(Field) . 从 这里 可以下载到完整的java代码工程: ? http://download.csdn.net/detail/hejiangtao/4011663

很多IOC等框架都使用反射来实现,例如Spring, Hibernate等, Java反射的方式实现的逻辑比普通类逻辑的效率是要差一些的(14至300倍左右), 具体可以参考我转载的一篇文章<java反射的性能问题 >http://blog.csdn.net/hejiangtao/article/details/7188835.

首先看下我们实例中被访问的类DataTypeBean.java:

这个Bean中定义了4种类型的Field,包含了int, String,String数组和List; 定义了默认构造函数和自定义的构造函数; 还有一个给List域赋值的带参数函数; 一个不带参数的toString函数.我们要实现的就是使用反射的方法来访问这些Fields 和Methods.

?

[html] view plain copy
  1. package?com.ross.reflect.bean;??
  2. import?java.util.*;??
  3. /**??
  4. ?*?Author:?Jiangtao?He;?Email:?ross.jiangtao.he@gmail.com??
  5. ?*?Date:?2012-1-4??
  6. ?*?Since:?MyJavaExpert?v1.0??
  7. ?*?Description:?It?will?contains?some?typical?fields?whose?data?types??
  8. ?*???are?using?frequently.?it?will?be?used?in?the?reflect?test??
  9. ?*/??
  10. public?class?DataTypeBean??
  11. {??
  12. ????private?int?iInt;??
  13. ????private?String?sStr;??
  14. ????private?String[]?saStr;??
  15. ????List< Integer > ?oList;??
  16. ??
  17. ????//?default?constructor??
  18. ????public?DataTypeBean()??
  19. ????{??
  20. ????}??
  21. ??
  22. ????//?constructor?with?parameters??
  23. ????public?DataTypeBean(int?iInt,?String?sStr,?String[]?saStr,??
  24. ????????????List< Integer > ?oList)??
  25. ????{??
  26. ????????this.iInt ?=?iInt;??
  27. ????????this.saStr ?=?saStr;??
  28. ????????this.sStr ?=?sStr;??
  29. ????????this.oList ?=?oList;??
  30. ????}??
  31. ??
  32. ????//?method?with?parameter,?it?will?set?value?of?the?list?field??
  33. ????public?void?addDataToList(int?iStart,?int?iEnd)??
  34. ????{??
  35. ????????if?(iStart?< ? iEnd )??
  36. ????????{??
  37. ????????????oList ?=? new ?ArrayList < Integer > ();??
  38. ????????????while?(iStart?< =?iEnd)??
  39. ????????????{??
  40. ????????????????oList.add(iStart);??
  41. ????????????????iStart++;??
  42. ????????????}??
  43. ????????}??
  44. ????}??
  45. ??
  46. ????//?method?without?parameter??
  47. ????public?String?toString()??
  48. ????{??
  49. ????????StringBuffer?sbStr ?=? new ?StringBuffer();??
  50. ????????sbStr.append("Values?of?the?fields?of?DataTypeBean:?iInt ?=?");??
  51. ????????sbStr.append(this.iInt).append("?;?");??
  52. ????????for?(int?i ?=? 0 ;?i? < ? this.saStr.length ;?i++)??
  53. ????????{??
  54. ????????????sbStr.append("saStr").append("[").append(i).append("]").append(??
  55. ????????????????????"?=?").append(saStr[i]).append("?;?");??
  56. ????????}??
  57. ??
  58. ????????for?(int?j ?=? 0 ;?j? < ? this.oList.size ();?j++)??
  59. ????????{??
  60. ????????????sbStr.append("oList.get").append("(").append(j).append(")").append(??
  61. ????????????????????"?=?").append(oList.get(j)).append("?;?");??
  62. ????????}??
  63. ????????return?sbStr.toString();??
  64. ????}??
  65. ??
  66. ????//省略了set/get方法??
  67. }??

来看我们的反射的实现类MyReflect.java, 由于担心代码太长不好看,就全部在Main函数里面写了,方便看.

1. 首先我们看下使用默认构造函数创建类对象, 并通过访问Field对象来给类对象赋值, 最后通过toString方法打印字符串.

初始化我们要使用的参数, 这些参数将用于给类的Field赋值:

[html] view plain copy
  1. int? iInt ?=? 2012 ;??
  2. String?sStr ?=? "This?a?string!" ;??
  3. String[]?saStr ?=? new ?String[]?{?"First?item?of?the?string?array",??
  4. ????????"Second?item?of?the?string?array",??
  5. ????????"Third?item?of?the?string?array"?};??
  6. List< Integer > ? oList ?=? new ?ArrayList < Integer > ();??
  7. ??
  8. //?Initialize?the?oList??
  9. int?i ?=? 0 ;??
  10. while?(i?< ? 3 )??
  11. {??
  12. ????oList.add(i);??
  13. ????i++;??
  14. }??
获取 DataTypeBean的类,和我们将要用到的方法对象, 其中toString方法是不带参数的,addDataToList则是带参数的. 由此可以看出我们在使用反射方法的时候是需要知道参数个数和参数类型的: [html] view plain copy
  1. //?get?class??
  2. Class?oClass ?=?Class.forName("com.ross.reflect.bean.DataTypeBean");??
  3. //?get?the?toString?method,?a?method?without?parameters??
  4. Method?oToStringMethod ?=? oClass .getMethod("toString");??
  5. //?get?the?addDataToList?method,?a?method?with?parameters??
  6. Method?oAddDataToListMethod ?=? oClass .getMethod("addDataToList",??
  7. ????????int.class,?int.class);??
使用默认构造函数创建一个 DataTypeBean的对象: [html] view plain copy
  1. //?used?default?constructor?to?initialize?a?object??
  2. Object?oDefalutObject ?=? oClass .newInstance();??
使用反射方法访问Field来给对象赋值: [html] view plain copy
  1. //?access?fields?process,?getDeclaredFields?can?access?private?and??
  2. //?protected?fields??
  3. Field[]?oFields ?=? oClass .getDeclaredFields();??
  4. for?(int?j ?=? 0 ;?j? < ? oFields.length ;?j++)??
  5. {??
  6. ????//?to?access?the?private??
  7. ????oFields[j].setAccessible(true);??
  8. ??
  9. ????//?getSimpleName?method?can?get?the?type?of?the?field,?according?the??
  10. ????//?field?type?set?the?data?to?the?field??
  11. ????if?("int".equals(oFields[j].getType().getSimpleName()))??
  12. ????{??
  13. ????????oFields[j].setInt(oDefalutObject,?iInt);??
  14. ????}??
  15. ????else?if?("String[]".equals(oFields[j].getType().getSimpleName()))??
  16. ????{??
  17. ????????oFields[j].set(oDefalutObject,?saStr);??
  18. ????}??
  19. ????else?if?("String".equals(oFields[j].getType().getSimpleName()))??
  20. ????{??
  21. ????????oFields[j].set(oDefalutObject,?sStr);??
  22. ????}??
  23. ????else?if?("List".equals(oFields[j].getType().getSimpleName()))??
  24. ????{??
  25. ????????oFields[j].set(oDefalutObject,?oList);??
  26. ????}??
  27. }??
通过反射方法调用 DataTypeBean的toString方法将赋值后的 DataTypeBean打印出来: [html] view plain copy
  1. //?print?the?object??
  2. String?sBeanString ?=?(String)?oToStringMethod.invoke(oDefalutObject);??
  3. System.out??
  4. ????????.println("the?string?of?the?object?created?by?defaut?constructor:?"??
  5. ????????????????+?sBeanString);??
运行后,我们的控制台打印出如下信息: [html] view plain copy
  1. the?string?of?the?object?created?by?defaut?constructor:?Values?of?the?fields?of?DataTypeBean:? iInt ?=? 2012 ?;???
  2. saStr[0]?=?First?item?of?the?string?array?;?saStr[1]?=?Second?item?of?the?string?array?;?saStr[2]?=?Third?item???
  3. of?the?string?array?;?oList.get(0)?=?0?;?oList.get(1)?=?1?;?oList.get(2)?=?2?;???

2. 我们再看下使用自定义构造函数创建类对象, 并通过带参数的函数给其List域赋值, 最后通过toString方法打印字符串.

变更下我们要用的参数, 好在控制台上跟默认构造函数创建的对象的打印信息做区分:

[html] view plain copy
  1. //?initialize?the?parameters?for?customized?constructor,?the?oList?will??
  2. //?be?initialized?by?the?method?with?parameters??
  3. iInt ?=? 2013 ;??
  4. sStr ?=? "This?another?string!" ;??
  5. saStr ?=? new ?String[]?{?"1st?item?of?the?string?array",??
  6. ????????"2nd?item?of?the?string?array",?"3rd?item?of?the?string?array"?};??
  7. oList ?=? new ?ArrayList < Integer > ();??
使用自定义构造函数创建类对象: [html] view plain copy
  1. //?used?customized?constructor?to?initialize?a?object:?DataTypeBean(int??
  2. //?iInt,?String?sStr,?String[]?saStr,?List< Integer > ?oList)??
  3. Constructor?oCon ?=? oClass .getConstructor(int.class,?String.class,??
  4. ????????String[].class,?List.class);??
  5. Object?oCustomizedObject ?=? oCon .newInstance(iInt,?sStr,?saStr,?oList);??
使用带参数的函数给List 域赋值: [html] view plain copy
  1. //Use?the?method?with?parameters?initialize?the?List?Object??
  2. ?oAddDataToListMethod.invoke(oCustomizedObject,2013,2015);??
同样的,通过反射方法调用 DataTypeBean的toString方法将赋值后的 DataTypeBean打印出来:
[html] view plain copy
  1. //?print?the?object??
  2. ???????sBeanString ?=?(String)?oToStringMethod.invoke(oCustomizedObject);??
  3. ???????System.out??
  4. ???????????????.println("the?string?of?the?object?created?by?customized?constructor:?"??
  5. ???????????????????????+?sBeanString);??
运行后,我们的控制台打印如下信息: [html] view plain copy
  1. the?string?of?the?object?created?by?customized?constructor:?Values?of?the?fields?of?DataTypeBean:? iInt ?=? 2013 ?;???
  2. saStr[0]?=?1st?item?of?the?string?array?;?saStr[1]?=?2nd?item?of?the?string?array?;?saStr[2]?=?3rd?item?of?the??
  3. ?string?array?;?oList.get(0)?=?2013?;?oList.get(1)?=?2014?;?oList.get(2)?=?2015?;?oList.get(3)?=?2016?;???

为了方便参考,我将完整的MyReflect.java贴出来了:

?

[html] view plain copy
  1. package?com.ross.reflect;??
  2. import?java.lang.reflect.Constructor;??
  3. import?java.lang.reflect.Field;??
  4. import?java.lang.reflect.InvocationTargetException;??
  5. import?java.lang.reflect.Method;??
  6. import?java.util.ArrayList;??
  7. import?java.util.List;??
  8. /**??
  9. ?*?Author:?Jiangtao?He;?Email:?ross.jiangtao.he@gmail.com??
  10. ?*?Date:?2012-1-9??
  11. ?*?Since:?MyJavaExpert?v1.0??
  12. ?*?Description:?reflect?method?implementation?and?test??
  13. ?*/??
  14. public?class?MyReflect??
  15. {??
  16. ????/**??
  17. ?????*?Author:?Jiangtao?He;?Email:?ross.jiangtao.he@gmail.com??
  18. ?????*?Date:?2012-1-9???
  19. ?????*?Description:?Use?reflect?method?to?access?the?fields?and?methods?of?DataTypebean??
  20. ?????*/??
  21. ????public?static?void?main(String[]?args)?throws?ClassNotFoundException,??
  22. ????????????SecurityException,?NoSuchMethodException,?InstantiationException,??
  23. ????????????IllegalAccessException,?IllegalArgumentException,??
  24. ????????????InvocationTargetException??
  25. ????{??
  26. ????????int?iInt ?=? 2012 ;??
  27. ????????String?sStr ?=? "This?a?string!" ;??
  28. ????????String[]?saStr ?=? new ?String[]?{?"First?item?of?the?string?array",??
  29. ????????????????"Second?item?of?the?string?array",??
  30. ????????????????"Third?item?of?the?string?array"?};??
  31. ????????List< Integer > ? oList ?=? new ?ArrayList < Integer > ();??
  32. ??
  33. ????????//?Initialize?the?oList??
  34. ????????int?i ?=? 0 ;??
  35. ????????while?(i?< ? 3 )??
  36. ????????{??
  37. ????????????oList.add(i);??
  38. ????????????i++;??
  39. ????????}??
  40. ????????//?get?class??
  41. ????????Class?oClass ?=?Class.forName("com.ross.reflect.bean.DataTypeBean");??
  42. ????????//?get?the?toString?method,?a?method?without?parameters??
  43. ????????Method?oToStringMethod ?=? oClass .getMethod("toString");??
  44. ????????//?get?the?addDataToList?method,?a?method?with?parameters??
  45. ????????Method?oAddDataToListMethod ?=? oClass .getMethod("addDataToList",??
  46. ????????????????int.class,?int.class);??
  47. ??
  48. ????????//?used?default?constructor?to?initialize?a?object??
  49. ????????Object?oDefalutObject ?=? oClass .newInstance();??
  50. ??
  51. ????????//?access?fields?process,?getDeclaredFields?can?access?private?and??
  52. ????????//?protected?fields??
  53. ????????Field[]?oFields ?=? oClass .getDeclaredFields();??
  54. ????????for?(int?j ?=? 0 ;?j? < ? oFields.length ;?j++)??
  55. ????????{??
  56. ????????????//?to?access?the?private??
  57. ????????????oFields[j].setAccessible(true);??
  58. ??
  59. ????????????//?getSimpleName?method?can?get?the?type?of?the?field,?according?the??
  60. ????????????//?field?type?set?the?data?to?the?field??
  61. ????????????if?("int".equals(oFields[j].getType().getSimpleName()))??
  62. ????????????{??
  63. ????????????????oFields[j].setInt(oDefalutObject,?iInt);??
  64. ????????????}??
  65. ????????????else?if?("String[]".equals(oFields[j].getType().getSimpleName()))??
  66. ????????????{??
  67. ????????????????oFields[j].set(oDefalutObject,?saStr);??
  68. ????????????}??
  69. ????????????else?if?("String".equals(oFields[j].getType().getSimpleName()))??
  70. ????????????{??
  71. ????????????????oFields[j].set(oDefalutObject,?sStr);??
  72. ????????????}??
  73. ????????????else?if?("List".equals(oFields[j].getType().getSimpleName()))??
  74. ????????????{??
  75. ????????????????oFields[j].set(oDefalutObject,?oList);??
  76. ????????????}??
  77. ????????}??
  78. ??
  79. ????????//?print?the?object??
  80. ????????String?sBeanString ?=?(String)?oToStringMethod.invoke(oDefalutObject);??
  81. ????????System.out??
  82. ????????????????.println("the?string?of?the?object?created?by?defaut?constructor:?"??
  83. ????????????????????????+?sBeanString);??
  84. ??
  85. ????????//?initialize?the?parameters?for?customized?constructor,?the?oList?will??
  86. ????????//?be?initialized?by?the?method?with?parameters??
  87. ????????iInt ?=? 2013 ;??
  88. ????????sStr ?=? "This?another?string!" ;??
  89. ????????saStr ?=? new ?String[]?{?"1st?item?of?the?string?array",??
  90. ????????????????"2nd?item?of?the?string?array",?"3rd?item?of?the?string?array"?};??
  91. ????????oList ?=? new ?ArrayList < Integer > ();??
  92. ??
  93. ????????//?used?customized?constructor?to?initialize?a?object:?DataTypeBean(int??
  94. ????????//?iInt,?String?sStr,?String[]?saStr,?List< Integer > ?oList)??
  95. ????????Constructor?oCon ?=? oClass .getConstructor(int.class,?String.class,??
  96. ????????????????String[].class,?List.class);??
  97. ????????Object?oCustomizedObject ?=? oCon .newInstance(iInt,?sStr,?saStr,?oList);??
  98. ????????//Use?the?method?with?parameters?initialize?the?List?Object??
  99. ????????oAddDataToListMethod.invoke(oCustomizedObject,2013,2015);??
  100. ??????????
  101. ????????//?print?the?object??
  102. ????????sBeanString ?=?(String)?oToStringMethod.invoke(oCustomizedObject);??
  103. ????????System.out??
  104. ????????????????.println("the?string?of?the?object?created?by?customized?constructor:?"??
  105. ????????????????????????+?sBeanString);??
  106. ????}??
  107. }??
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