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The MyBatis SQL mapper framework makes it easier to use a relational database with object-oriented applications. MyBatis couples objects with stored procedures or SQL statements using a XML descriptor or annotations. Simplicity is the biggest advantage of the MyBatis data mapper over object relational mapping tools.

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package org.apache.ibatis.binding;

import java.io.Serializable;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

import org.apache.ibatis.session.SqlSession;

public class MapperProxy implements InvocationHandler, Serializable {

  private static final long serialVersionUID = -6424540398559729838L;
  private SqlSession sqlSession;

  private  MapperProxy(SqlSession sqlSession) {
    this.sqlSession = sqlSession;
  }

  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    if (method.getDeclaringClass() == Object.class) {
      return method.invoke(this, args);
    }
    final Class declaringInterface = findDeclaringInterface(proxy, method);
    final MapperMethod mapperMethod = new MapperMethod(declaringInterface, method, sqlSession);
    final Object result = mapperMethod.execute(args);
    if (result == null && method.getReturnType().isPrimitive() && !method.getReturnType().equals(Void.TYPE)) {
      throw new BindingException("Mapper method '" + method.getName() + "' (" + method.getDeclaringClass() + ") attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");
    }
    return result;
  }

  private Class findDeclaringInterface(Object proxy, Method method) {
    Class declaringInterface = null;
    for (Class iface : proxy.getClass().getInterfaces()) {
      try {
        Method m = iface.getMethod(method.getName(), method.getParameterTypes());
        if (declaringInterface != null) {
          throw new BindingException("Ambiguous method mapping.  Two mapper interfaces contain the identical method signature for " + method);
        } else if (m != null) {
          declaringInterface = iface;
        }
      } catch (Exception e) {
        // Intentionally ignore.
        // This is using exceptions for flow control,
        // but it's definitely faster.
      }
    }
    if (declaringInterface == null) {
      throw new BindingException("Could not find interface with the given method " + method);
    }
    return declaringInterface;
  }

  @SuppressWarnings("unchecked")
  public static  T newMapperProxy(Class mapperInterface, SqlSession sqlSession) {
    ClassLoader classLoader = mapperInterface.getClassLoader();
    Class[] interfaces = new Class[]{mapperInterface};
    MapperProxy proxy = new MapperProxy(sqlSession);
    return (T) Proxy.newProxyInstance(classLoader, interfaces, proxy);
  }

}