servlet 中处理 json 请求，并访问 service 类，返回处理结果

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前言：jar 包中的 servlet 必须可以处理前端发出的 ajax 请求，接收参数，并返回结果。

github地址：yuleGH github

这里有个约定，url 地址是 .json 结尾的，如果是 .json 结尾的则当成 ajax 访问，如果不是，则当成查找普通文件处理。

处理 json 请求的异常处理方式：

if (path.endsWith(".json")){
try{
//处理ajax请求
dealJsonService(request, response, path);
} catch (Exception e){
logger.error("访问querydb ajax报错！", e);
response.setStatus(500);
response.getWriter().write("服务器端未知错误：" + e.getMessage());
}
}

处理 json 请求的核心处理方法（通过反射设定参数并调用业务方法，然后返回 json 结果）：

/**
* 处理ajax的json请求
* @param request
* @param response
* @param path
* @throws IOException
* @throws NoSuchMethodException
* @throws InvocationTargetException
* @throws IllegalAccessException
* @throws InstantiationException
*/
private void dealJsonService(HttpServletRequest request, HttpServletResponse response, String path) throws IOException, NoSuchMethodException, InvocationTargetException, IllegalAccessException, InstantiationException {
String methodName = path.substring(1, path.indexOf(".json")); final Method[] methods = DbComponentTopService.class.getMethods();
boolean flag = false;
for(Method method : methods){
if(method.getName().equals(methodName)){
flag = true;
Object objResult = getObjResultByMethod(request, response, method);
if(objResult != null){
Gson gson = new Gson();
response.getWriter().print(gson.toJson(objResult));
}
break;
}
} if(!flag){
logger.error("404-找不到地址：{}", path);
response.setStatus(404);
response.getWriter().write("404-找不到地址：" + path);
}
}

执行获取结果的方法（绑定参数，利用自定义注解和反射）：

/**
* 执行方法，获取结果值
* @param request
* @param response
* @param method
* @return
* @throws InvocationTargetException
* @throws IllegalAccessException
* @throws NoSuchMethodException
*/
private Object getObjResultByMethod(HttpServletRequest request, HttpServletResponse response, Method method) throws InvocationTargetException, IllegalAccessException, NoSuchMethodException {
Object objResult = null; String methodName = method.getName();
DbComponentTopService dbComponentTopService = SpringContextHolder.getBean(DbComponentTopService.class);
//方法的参数类型
final Class<?>[] parameterTypes = method.getParameterTypes();
//存放方法的参数值
final Object[] parameterValues = new Object[parameterTypes.length];
int i = 0; if(CommonUtil.isNullOrBlock(parameterTypes)){
Method myMethod = DbComponentTopService.class.getMethod(methodName);
objResult = myMethod.invoke(dbComponentTopService);
}else{
//获取方法的参数注解
final Annotation[][] parameterAnnotations = method.getParameterAnnotations();
for (Annotation[] annotation1 : parameterAnnotations) {
for (Annotation annotation : annotation1) {
if (annotation instanceof MyParam) {
MyParam customAnnotation = (MyParam) annotation;
Class curParameterType = parameterTypes[i]; if("httpServletRequest".equals(customAnnotation.value())){
parameterValues[i++] = request;
}else if ("httpServletResponse".equals(customAnnotation.value())){
parameterValues[i++] = response;
}else if ("java.lang.Integer".equals(curParameterType.getName())){
parameterValues[i++] = Integer.parseInt(request.getParameter(customAnnotation.value()));
}else{
parameterValues[i++] = request.getParameter(customAnnotation.value());
}
}
}
} Method myMethod = DbComponentTopService.class.getMethod(methodName, parameterTypes);
objResult = myMethod.invoke(dbComponentTopService, parameterValues);
} return objResult;
}