本文导引：

　　通过反射机制

1 package reflection; 2  3 @AnnotationUserTable("datebaseExample") 4 public class User { 5     @AnnotationUserField(uName="name",type="varchar",length=10) 6     private String name; 7     @AnnotationUserField(uName="age",type="int",length=3) 8     private int age; 9     @AnnotationUserField(uName="sex",type="char",length=2)10     private String sex;11     12     public User() {13         super();14     }15     16     public User(String name, int age, String sex) {17         super();18         this.name = name;19         this.age = age;20         this.sex = sex;21     }22     23     public String getName() {24         return name;25     }26     public void setName() {27         this.name = "test";28     }29     public int getAge() {30         return age;31     }32     public String getSex() {33         return sex;34     }35     public void setSex(String sex) {36         this.sex = sex;37     }38 }

1 package reflection; 2  3 import java.lang.annotation.ElementType; 4 import java.lang.annotation.Retention; 5 import java.lang.annotation.RetentionPolicy; 6 import java.lang.annotation.Target; 7  8 @Target(value={ElementType.TYPE}) 9 @Retention(RetentionPolicy.RUNTIME) 10 public @interface AnnotationUserTable {11     String value();12 }

1 package reflection; 2  3 import java.lang.annotation.ElementType; 4 import java.lang.annotation.Retention; 5 import java.lang.annotation.RetentionPolicy; 6 import java.lang.annotation.Target; 7  8 @Target(value={ElementType.FIELD}) 9 @Retention(RetentionPolicy.RUNTIME)10 public @interface AnnotationUserField {11     String uName();12     String type();13     int length();    14 }

1 package reflection; 2  3 import java.lang.reflect.Constructor; 4 import java.lang.reflect.Field; 5 import java.lang.reflect.Method; 6  7 public class Demo01 { 8     static Class
       c = null; 9     public static void main(String[] args) {10             try {11                 c = Class.forName("reflection.User");12             } catch (ClassNotFoundException e) {13                 e.printStackTrace();14             }15         test();//获取类的属性、方法等信息16         17     }18     static void test(){19         try {20             // 获取类的名称21             System.out.println("获取类的名称");22             System.out.println("getName():" + c.getName());// 获得包名+类名23             System.out.println("getSimpleName():" + c.getSimpleName());// 获得类名24             System.out.println("getCanonicalName():" + c.getCanonicalName());// 获得类名25             System.out.println("*******************************");26             // 获取属性信息27             System.out.println("获取属性信息");28             Field[] fields = c.getDeclaredFields();29             // Field[] fields = c.getFields(); 只能获取public修饰的属性信息30             for (Field f : fields) {31                 String fName = f.getName();32                 System.out.println(c.getDeclaredField(fName));33             }34             System.out.println("*******************************");35             // 获取方法信息36             System.out.println("获取方法信息");37             Method[] methods = c.getDeclaredMethods();38             for (Method m : methods) {39                 // String mName = m.getName();40                 System.out.println(m.getName() + "-->" + m);41             }42             System.out.println("通过名称单独获取对应的getName方法:" + c.getDeclaredMethod("getName"));43             System.out.println("通过名称单独获取对应的setSex方法:" + c.getDeclaredMethod("setSex", String.class));// 方法有参，必须传递参数类型44             System.out.println("*******************************");45             // 获取构造器信息46             System.out.println("获取构造器信息");47             Constructor
      [] constructor = c.getConstructors();48             for (Constructor
       cons : constructor) {49                 System.out.println(cons);50             }51         } catch (NoSuchFieldException | SecurityException e) {52             e.printStackTrace();53         } catch (NoSuchMethodException e) {54             e.printStackTrace();55         }56     }57 }

output：

获取类的名称getName():reflection.UsergetSimpleName():UsergetCanonicalName():reflection.User*******************************获取属性信息private java.lang.String reflection.User.nameprivate int reflection.User.ageprivate java.lang.String reflection.User.sex*******************************获取方法信息getName-->public java.lang.String reflection.User.getName()setName-->public void reflection.User.setName()setSex-->public void reflection.User.setSex(java.lang.String)getSex-->public java.lang.String reflection.User.getSex()getAge-->public int reflection.User.getAge()通过名称单独获取对应的getName方法:public java.lang.String reflection.User.getName()通过名称单独获取对应的setSex方法:public void reflection.User.setSex(java.lang.String)*******************************获取构造器信息public reflection.User()public reflection.User(java.lang.String,int,java.lang.String)

 

下面的例子，是通过反射机制获取类的注解信息。

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1 package reflection; 2  3 import java.lang.reflect.Field; 4 /** 5  * 获取类的属性、方法等信息 6  * 1.获取元素对象（如属性）（注意：读取类的注解，看似要少一步） 7  * 2.获取该元素对象的指定类型的注解对象 8  * 3.读取注解对象相应的值 9  */10 public class Test02 {11     static Class
      c = null;12     public static void main(String[] args) {13             try {14                 c = Class.forName("reflection.User");15             } catch (ClassNotFoundException e) {16                 e.printStackTrace();17             }18         test();19     }20 21     static void test(){22         try {23             // 获取类的指定注解24             System.out.println("***********类的指定注解**************");25             AnnotationUserTable table = (AnnotationUserTable)c.getAnnotation(AnnotationUserTable.class);26             System.out.println(table.value());27             28             // 获取属性的指定注解29             System.out.println("***********属性的指定注解*************");30             Field field = c.getDeclaredField("name");31             AnnotationUserField annoField = (AnnotationUserField)field.getAnnotation(AnnotationUserField.class);32             System.out.println(annoField.uName()+"\t"+annoField.type()+"\t"+annoField.length());33             34             // 根据获得的表名、字段的信息，拼写出DDL语句，然后通过JDBC连接数据库查询35         } catch (NoSuchFieldException e) {36             e.printStackTrace();37         } catch (SecurityException e) {38             e.printStackTrace();39         }40     }41 }

output:

***********类的指定注解**************datebaseExample***********属性的指定注解*************name    varchar    10

 

下面的例子，是通过反射机制获取泛型信息

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1 package reflection; 2  3 import java.lang.reflect.Method; 4 import java.lang.reflect.Type; 5 import java.util.List; 6 import java.util.Map; 7  8 /** 9  * 通过反射机制获取泛型10  * @author Administrator11  *12  */13 public class Test03 {    14     public static void main(String[] args) {15         Class
       c = Test03.class;16         try {17             System.out.println("*******获取参数值的类型**********");18             Method m1 = c.getDeclaredMethod("method01", Map.class,List.class);19             Type[] types = m1.getGenericParameterTypes();20             for(Type t:types){21                 System.out.println(t.getTypeName());22                 System.out.println(t.toString());                23             }24             System.out.println("*******获取返回值的类型**********");25             Method m2 = c.getDeclaredMethod("method02");26             Type ret = m2.getGenericReturnType();27             System.out.println(ret.getTypeName());28             System.out.println(ret.toString());29         } catch (NoSuchMethodException | SecurityException e) {30             e.printStackTrace();31         }32     }33     34     public void method01(Map
      
        args1,List
       
         args2){35         36     }37     public Map
        
          method02(){38         return null;39     }40 }
        
       
      

output:

java.util.Map
      
       java.util.Map
       
        java.util.Map
        
         java.util.Map
         
          java.util.List
          
           java.util.List