时间戳

首页 > 解决方案 > ResultSet 异常 - 开始之前

java - ResultSet 异常 - 开始之前

问题描述

    public static User getUser (User user) throws Exception {
            String sql = "SELECT * FROM login WHERE userID = '" + user.getuserID() + "'";
            //is FROM Correct?
            PreparedStatement pStatement = conn.prepareStatement(sql);
            ResultSet Rset = pStatement.executeQuery(sql);
            Rset.beforeFirst();
            Rset.next();

            int userID = Rset.getInt("userID");
            String email = Rset.getString("email");
            User userReturn = new User (userID, email);
            return userReturn;
        }


Trace: java.sql.SQLException: Operation not allowed for a result set of type ResultSet.TYPE_FORWARD_ONLY.
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:129)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97)
    at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122)
    at com.mysql.cj.jdbc.result.ResultSetImpl.beforeFirst(ResultSetImpl.java:426)
    at DaoLayer.daoImplementation.getUser(daoImplementation.java:28)
    at DaoLayer.DaoTest.testGetUser(DaoTest.java:26)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
    at org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)
    at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
    at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
    at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:413)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:89)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:41)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:542)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:770)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:464)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:210)

标签： javajdbcsinglestore

解决方案

创建标准时ResultSet，您只能使用rs.next()方法来迭代结果行。所以rs.beforeFirst()是不允许的。而且在您的代码中也没有必要。创建ResultSet时，光标会自动放置在第一行之前。所以，只使用if(rs.next()) {...}. 当rs.next()第一次调用后返回 false 时，表示ResultSet为空。

推荐阅读