ajax中设置contentType: “application/json”的作用

最近在做项目交互的时候，刚开始向后台传递数据返回415，后来百度添加了 contentType："application/json" 之后返回400，然后把传输的数据格式改为json字符串就传输成功了，现在我们来看看 contentType：“application/json“的作用：

添加 contentType：“application/json“之后，向后台发送数据的格式必须为json字符串

$.ajax({
    type: "post",
    url:  "mobile/notice/addMessageInfo.jspx",
    contentType: "application/json",
    data:"{'name':'zhangsan','age':'15'}",
    dataType: "json",
    success: function(data) {
        console.log(data);
    },
    error: function(msg) {
        console.log(msg)
    }
})

不添加 contentType：“application/json“的时候可以向后台发送json对象形式

$.ajax({
    type: "post",
    url:  "mobile/notice/addMessageInfo.jspx",
    data:{name:'zhangsan',age:'15'},
    dataType: "json",
    success: function(data) {
        console.log(data);
    },
    error: function(msg) {
        console.log(msg)
    }
})

另外，当向后台传递复杂json的时候，同样需要添加 contentType：“application/json“，然后将数据转化为字符串

var data = {
    uploadarray: uploadarray,
    messageInfo: {
        messageTitle: messageTitle,
        messageContent: messageContent,
        publisher: publisher
    },
    userId: userId
}

$.ajax({  
    type: 'post',
    url: "mobile/notice/addMessageInfo.jspx",
    contentType: 'application/json',
    data: JSON.stringify(data),
    dataType: "json",
    success: function(data) {
        console.log(data);
    },
    error: function(msg) {
        console.log(msg)
    }
})