• Executor
• ParameterHandler
• ResultSetHandler

• StatementHandler

  8.1 拦截器接口介绍

  public interface Interceptor {
    Object intercept(Invocation var1) throws Throwable;
    Object plugin(Object target);
    void setProperties(Properties var1);
  }

  setProperties用来传递插件的参数，可以通过参数来改变插件的行为
  参数值传递：

    <plugins>
        <plugin interceptor="com.ql.simple.plugin.***INterceptor">
            <property name="prop1" value="value1"/>
            <property name="prop2" value="value2"/>
        </plugin>
    </plugins>

  plugin方法参数target就要拦截器要拦截的对象，该方法会在创建被拦截的接口实现类时被调用，只需要调用MyBatis提供的Plugin类的wrap静态方法就可以通过java的动态代理拦截目标对象

  @Overrride
  public Object plugin(Object target){
    return Plugin.wrap(target, this);
  }

  wrap方法会自动判断拦截器的前面和被拦截器对象的接口是否匹配，只有匹配的情况下才会使用动态代理拦截目标对象，因此上面不用做额外的逻辑判断

intercept是MyBatis运行时要执行的拦截方法：

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        Object target = invocation.getTarget();
        Method method = invocation.getMethod();
        Object[] args = invocation.getArgs();
        Object result = invocation.proceed();
        return result;
    }

invocation.proceed();执行被拦截对象真正的方法

8.2 拦截器签名介绍

• @Intercepts
• @Signature

用来配置拦截器要拦截的接口的方法

@Intercepts({
        @Signature(
                type = ResultSetHandler.class,
                method = "handleResultSets",
                args = {Statement.class})      
})
public class DemoInterceptor implements Interceptor {

8.2.1 Executor接口

• update
• query
• queryCursor
• flushStatements
• commit
• rollback
• getTransaction
• close

• isClosed

  8.2.2 ParameterHandler

  8.3 下划线键值转小写驼峰形式插件

  @Intercepts(@Signature(type = ResultSetHandler.class, method = "handleResultSets", args = {Statement.class}))
  @SuppressWarnings({"unchecked", "rawtypes"})
  public class CameHumpInterceptor implements Interceptor {
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        // 先执行得到结果，再对结果进行处理
        List<Object> list = (List<Object>) invocation.proceed();
        for (Object o : list) {
            // 如果结果是Map类型，就对Map的key进行转换
            if (o instanceof Map) {
                processMap((Map) o);
            }else {
                break;
            }
        }
        return list;
    }
    private void processMap(Map<String, Object> map) {
        Set<String> keySet = new HashSet<>(map.keySet());
        for (String key : keySet) {
            // 将以大写开头的字符串转换为小写，如果包含下划线也会处理为驼峰
            // 此处只通过这两个简单的表示来判断是否进行转换
            if ((key.charAt(0) >= 'A' && key.indexOf(0) <= 'Z') || key.indexOf("_") >= 0){
                Object value = map.get(key);
                map.remove(key);
                map.put(underlineToCamelhump(key), value);
            }
        }
    }
    public static String underlineToCamelhump(String inputString){
        StringBuffer sb = new StringBuffer();
        boolean nextUpperCase = false;
        for (int i = 0; i < inputString.length(); i++) {
            char c = inputString.charAt(i);
            if (c == '_'){
                if (sb.length() > 0) {
                    nextUpperCase = true;
                }
            }else {
                if (nextUpperCase) {
                    sb.append(Character.toUpperCase(c));
                    nextUpperCase = false;
                }else {
                    sb.append(Character.toLowerCase(c));
                }
            }
        }
        return sb.toString();
    }
    @Override
    public Object plugin(Object o) {
        return Plugin.wrap(o, this);
    }
    @Override
    public void setProperties(Properties properties) {
    }
  }

  8.4 分页插件