首先说下这个问题很坑,append的Js的object类型无效,我们后台用的是java
上错不成功的代码

let url = 'http://192.168.1.120:8090/app/release';
        let params = {parentId: "0", text: this.state.textContent, postType: , profitType: }
        let formdata = new FormData();
        formdata.append('file', {uri: this.state.envURL[].uri, type: 'image/jpg', name: 'image.jpg'});
        formdata.append('appUserPost', String(params));
        fetch(url, {
            method: 'post',
            headers: {
                'Content-Type': 'multipart/form-data; boundary=6ff46e0b6b5148d984f148b6542e5a5d',
            body: formdata
        }).then(response => {
            console.log("image uploaded")
        }).catch(err => {
            console.log(err)

正确的是拆分object
成功的代码

let url = 'http://192.168.0.89:8080/app/release';
        var appUserPost = { 'appUserPost': params, type: 'application/octet-stream' }
        var file = { uri: this.state.envURL, type: 'multipart/form-data', name: 'image.png' }
        let formdata = new FormData();
        formdata.append('file', file); // you can append anyone.
        formdata.append('parentId', "0")
        formdata.append('text', "asdfasd")
        formdata.append('postType', )
        formdata.append('profitType', )
        console.log("formdata", JSON.stringify(formdata))
        fetch(url, {
            method: 'POST',
            headers: {
                'Accept': 'application/json',
                // 'Content-Type': 'multipart/form-data',
            processData: false,
            contentType: false,
            body: formdata
        }).then(function (response) {
            console.log(response)
        }).catch(err => {
            console.log(err)
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原文链接：https://blog.csdn.net/u011135887/article/details/78600621