Java Maven Servlet API用于从数据库读取数据

Question

我正在尝试为学校项目制作一个简单的Web应用程序。我正在使用Java Maven，使用NetBeans中的servlet作为后端并使用vuejs脚本作为前端来编写API，服务器为GlassFish 4.1.1。问题是我没有从数据库中得到任何东西！

我有一个MySQL类：

public class MySQL implements Closeable {
    static{
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
        } catch (ClassNotFoundException ex) {
            Logger.getLogger(MySQL.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
    ThreadLocal<Connection> conn=new ThreadLocal<>();
    String url;
    String user;
    String pass;

    public MySQL(String server, String schema, String user, String pass) {
        this.url = String.format("jdbc:mysql://%s/%s",server,schema);
        //conn = DriverManager.getConnection(url, user, pass);
        this.user=user;
        this.pass=pass;
    }

    private Connection getConnection() throws SQLException {
        try{
            Class.forName("com.mysql.jdbc.Driver");
        }catch (ClassNotFoundException ex){
            Logger.getLogger(MySQL.class.getName()).log(Level.SEVERE, url);
        }
        Connection c=conn.get();
        if(c==null){
            c=DriverManager.getConnection(url, user, pass);
            conn.set(c);
                    }
        return c;
    }

    public ResultSet query(String sql, Object ... params) throws SQLException{
        PreparedStatement s=getConnection().prepareStatement(sql,ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_UPDATABLE);
         for(int i=0; i<params.length; i++) {
           s.setObject(i+1, params[i]);
        }
        return s.executeQuery();
    }

    public List<Integer> execute(String sql, Object ... params) throws SQLException {
        PreparedStatement s=getConnection().prepareStatement(sql, Statement.RETURN_GENERATED_KEYS);
        for(int i=0; i<params.length; i++) {
           s.setObject(i+1, params[i]);
        }
        s.execute();
        ResultSet r=s.getGeneratedKeys();
        List<Integer> keys=new ArrayList<>();
        while(r.next()) {
            keys.add(r.getInt(1));
        };
        r.close();
        s.close();
        return keys;
    }  

    public void close() {
        try {
           getConnection().close();
        } catch (SQLException ex) {          
        }
    }
}

我有一个在每个servlet中使用的Util类：

public class Util {

 public static void copy(InputStream in, OutputStream out) throws IOException {
        byte buffer[] = new byte[32 * 1024];
        while (true) {
            int t = in.read(buffer);
            if (t <= 0) {
                break;
            }
            out.write(buffer, 0, t);
        }
    }

    public static void writeResult(HttpServletResponse response, String message) throws IOException {
        response.setContentType("application/json");
        JSONObject res = new JSONObject();
        res.put("result", message);
        try (PrintWriter out = response.getWriter()) {
            out.print(res.toString());
        }
    }

    public static String getContent(HttpServletRequest request) throws IOException {
        BufferedReader r=request.getReader();
        StringBuilder sb=new StringBuilder();
        char[] buf=new char[2048];
        int cnt;
        do {
            cnt=r.read(buf);
            sb.append(buf,0,cnt);
        } while(cnt==buf.length);
        return sb.toString();
    }

    public static JSONObject getJSON(HttpServletRequest request) throws IOException {
        return new JSONObject(getContent(request));
    }
}

我的servlet，用于从数据库读取数据：

@WebServlet(name = "Centri", urlPatterns = {"/centri/api"})
public class Centri extends HttpServlet {

    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws SQLException, ServletException, IOException {
        response.setContentType("application/json");
        JSONArray jsa = new JSONArray();

        String id = request.getParameter("cnt_id");
        String ime = request.getParameter("cnt_ime");
        String planina = request.getParameter("cnt_planina");
        String duzStaza = request.getParameter("cnt_duzStaza");

        try (ResultSet rs = Main.db.query("SELECT * FROM centri")) {
            while (rs.next()) {
                JSONObject obj = Util.getJSON(request);
                obj.put("id", rs.getInt("cnt_id"));
                obj.put("ime", rs.getString("cnt_ime"));
                obj.put("planina", rs.getString("cnt_planina"));
                obj.put("duzStaza", rs.getString("cnt_duzStaza"));
                jsa.put(obj);
            }
              Util.getContent(request);
                     }
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        try {
            processRequest(request, response);
        } catch (SQLException ex) {
            Logger.getLogger(Centri.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        try {
            processRequest(request, response);
        } catch (SQLException ex) {
            Logger.getLogger(Centri.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    @Override
    public String getServletInfo() {
        return "Short description";
    }// </editor-fold>
}

我的前vue js：

const Centri = {
    data() {
        return{
            centri: []
        }
    },
    methods: {
        getCentri() {
            axios.get("http://localhost:8080/ItaProjekatTest/centri", null, data => this.centri = data)
        }
    },
    mounted() {
        this.getCentri()
    },
    template: ` <div class="cent">

                    <table>
                        <tr><th>ID</th></tr><tr><th>Ime</th></tr><tr><th>Planina</th></tr><tr><th>Duzina Staza</th></tr>
                        <tr v-for="centar in centri">

                         <td>{{centar.id}}</td>
                        <td>{{centar.ime}}</td>
                        <td>{{centar.planina}}</td>
                        <td>{{centar.duzStaza}}</td>

                        </tr>
                </table>

            </div>`
}

POM XML：

<dependencies>
        <dependency>
            <groupId>javax</groupId>
            <artifactId>javaee-web-api</artifactId>
            <version>7.0</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
        <dependency>
            <groupId>org.json</groupId>
            <artifactId>json</artifactId>
            <version>20180813</version>
        </dependency>

我从控制台日志中得到的错误是：

  

错误：请求失败，状态码为404 3 axios.min.js：8：6410

很抱歉，如果这些时间太长，但是我是初学者，需要答案。