如何使用struts2上传画布图像

Question

＆＃13;

＆＃13;

canvas = document.getElementById('can');
     ctx = canvas.getContext("2d");
     w = canvas.width;
     h = canvas.height;
 
     canvas.addEventListener("mousemove", function (e) {
         findxy('move', e)
     }, false);
     canvas.addEventListener("mousedown", function (e) {
         findxy('down', e)
     }, false);
     canvas.addEventListener("mouseup", function (e) {
         findxy('up', e)
     }, false);
     canvas.addEventListener("mouseout", function (e) {
         findxy('out', e)
     }, false); 
     
      var canvas, ctx, flag = false,
        prevX = 0,
        currX = 0,
        prevY = 0,
        currY = 0,
        dot_flag = false;

    var x = "black",
        y = 2;
    function init() {
        canvas = document.getElementById('can');
        ctx = canvas.getContext("2d");
        w = canvas.width;
        h = canvas.height;
    
        canvas.addEventListener("mousemove", function (e) {
            findxy('move', e)
        }, false);
        canvas.addEventListener("mousedown", function (e) {
            findxy('down', e)
        }, false);
        canvas.addEventListener("mouseup", function (e) {
            findxy('up', e)
        }, false);
        canvas.addEventListener("mouseout", function (e) {
            findxy('out', e)
        }, false);
    }
    
    function color(obj) {
        switch (obj.id) {
            case "green":
                x = "green";
                break;
            case "blue":
                x = "blue";
                break;
            case "red":
                x = "red";
                break;
            case "yellow":
                x = "yellow";
                break;
            case "orange":
                x = "orange";
                break;
            case "black":
                x = "black";
                break;
            case "white":
                x = "white";
                break;
        }
        if (x == "white") y = 14;
        else y = 2;
    
    }
    
    function draw() {
        ctx.beginPath();
        ctx.moveTo(prevX, prevY);
        ctx.lineTo(currX, currY);
        ctx.strokeStyle = x;
        ctx.lineWidth = y;
        ctx.stroke();
        ctx.closePath();
    }
    
    function erase() {
        var m = confirm("Want to clear");
        if (m) {
            ctx.clearRect(0, 0, w, h);
            document.getElementById("canvasimg").style.display = "none";
        }
    }
    
    function save() {
        document.getElementById("canvasimg").style.border = "2px solid";
        var dataURL = canvas.toDataURL();
        document.getElementById("canvasimg").src = dataURL;
        document.getElementById("canvasimg").style.display = "inline";
    }
    
    function findxy(res, e) {
        if (res == 'down') {
            prevX = currX;
            prevY = currY;
            currX = e.clientX - canvas.offsetLeft;
            currY = e.clientY - canvas.offsetTop;
    
            flag = true;
            dot_flag = true;
            if (dot_flag) {
                ctx.beginPath();
                ctx.fillStyle = x;
                ctx.fillRect(currX, currY, 2, 2);
                ctx.closePath();
                dot_flag = false;
            }
        }
        if (res == 'up' || res == "out") {
            flag = false;
        }
        if (res == 'move') {
            if (flag) {
                prevX = currX;
                prevY = currY;
                currX = e.clientX - canvas.offsetLeft;
                currY = e.clientY - canvas.offsetTop;
                draw();
            }
        }
    }

＆＃13;

<canvas id="can" width="600" height="300"
				style=" border: 2px solid darkgrey;border-radius: 10px;margin: 2px 2px 2px 2px;"></canvas>
				<img id="canvasimg" name="canvasimg" style="position:absolute;top:10%;left:52%;" style="display:none"/>
				<input type="file" id="userImage" name="userImage" />

＆＃13;

＆＃13;

＆＃13;

伙计我是编程新手，我真的不知道如何将div中显示的照片保存到服务器。我正在使用java应用程序，我试图在div上显示图像，然后将其保存在服务器上。据我所知，由于客户端和服务器的兼容性，无法在jsp或servlet中声明javascript变量。我试图通过ajax传递dataURL，但由于base64长字符串，它没有显示在服务器上。我想我们不能将这么长的字符串传递给jsp或servlet页面。有没有其他方法可以传递字符串或将图像保存到服务器？