servlet如何接收Json数据？如何向客户端发送Json数据？

HttpSession session = request.getSession();
request.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
ICarbrandBiz icarbranb=new CarbrandBizImpl();
Debug.p("***************ajax 读取 ********************");
Debug.p("获取数据");
String entityname=request.getParameter("entityname");
String str=request.getParameter("properties");
Debug.p("entityname:"+entityname+"\n"+"properties:"+str);
String[] properties=str.split("\\*");
Debug.p("构建SQL原型");
String hql=" from "+entityname;
String hql2=null;
for (int i = 0; i < properties.length; i++) {
if(i==0){
hql2="select "+properties[i];
}else {
hql2+=","+properties[i];
}
}
Debug.p("SQl："+hql2+hql);
List<Object[]> list=HibernateUtil.selectsql(hql2+hql, null);
if(list==null||list.size()==0){
Debug.p("{\"err\":\"0\"}");
out.write("{\"err\":\"0\"}");
out.flush();
out.close();
return;
}
Debug.p("数据转换");
if(list.get(0).length>0){
Debug.p("json转换");
String data="\"err\":\"1\",\"data\":[";
int a=0;
for (Object[] i : list) {
String za="";
for (int j = 0; j < i.length; j++) {
if(j==0){
za+="\""+j+"\":\""+i[j]+"\"";
}else {
za+=",\""+j+"\":\""+i[j]+"\"";
}
}
if(a==0){
data+="{"+za+"}";
a++;
}else {
data+=",{"+za+"}";
}
}
Debug.p("输出数据：{"+data+"]}");
out.write("{"+data+"]}");
}
out.flush();
out.close();
return;