Spring boot Kotlin JdbcTemplate Null

我正在尝试将我的应用程序从java转换为kotlin，目前正在使用java和kotlin的混合。我正在尝试首先将我的存储库类转换为Kotlin。这是使用SpringJDBC。我做错什么了吗

package com.meteor.coral.resources.useradministration.domain

import org.springframework.beans.factory.annotation.Autowired
import org.springframework.jdbc.core.JdbcTemplate
import org.springframework.jdbc.core.RowMapper
import org.springframework.stereotype.Repository
import java.sql.ResultSet
import java.sql.SQLException

@Repository
open class AppUserJdbcRepository {

    @Autowired
    private var jdbcTemplate: JdbcTemplate? = null

    fun findByFirstName(firstName: String): AppUser {
        print("hello")
        return jdbcTemplate!!.queryForObject("select firstname, lastname from m_appuser where firstname = ?", arrayOf<Any>(firstName), AppUserRowMapper())
    }



    internal inner class AppUserRowMapper : RowMapper<AppUser> {
        @Throws(SQLException::class)
        override fun mapRow(resultSet: ResultSet, i: Int): AppUser {
            val appUser = AppUser(resultSet.getString("firstname"),resultSet.getString("lastName") )
            return appUser
        }
    }
}

jdbctemplate始终为空

hello
java.lang.NullPointerException
    at com.meteor.coral.resources.useradministration.domain.AppUserJdbcRepository.findByFirstName(AppUserJdbcRepository.kt:18)
    at com.meteor.coral.resources.useradministration.AppUserJdbcRepositoryTest.testAppFetch(AppUserJdbcRepositoryTest.java:25)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    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.springframework.test.context.junit4.statements.RunBeforeTestExecutionCallbacks.evaluate(RunBeforeTestExecutionCallbacks.java:74)
    at org.springframework.test.context.junit4.statements.RunAfterTestExecutionCallbacks.evaluate(RunAfterTestExecutionCallbacks.java:84)
    at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
    at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
    at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:251)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:97)
    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.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
    at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
    at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:413)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:190)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
    at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
    at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:220)
    at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:53)

---

谢谢，

在kotlin中使用spring进行属性注入需要lateinit关键字：

@Autowired
private lateinit var jdbcTemplate: JdbcTemplate

通常，您希望进行构造函数注入，因为这允许您删除自动连线注释并将其设置为val：

class AppUserJdbcRepository(private val jdbcTemplate: JdbcTemplate){

---

为了完整性：您不应该（忽略罕见的情况）使用“！！”在kotlin中使用运算符，因为这基本上是回到Java的可空性方法。至少在我的经验中，用“？：throw MyCustomException（“jdbcTemplate在初始化期间为null”）”重新放置它更易于调试，我经常发现考虑它也会暴露出不必要的可空性。

在kotlin中使用spring的属性注入需要lateinit关键字：

@Autowired
private lateinit var jdbcTemplate: JdbcTemplate

通常，您希望进行构造函数注入，因为这允许您删除自动连线注释并将其设置为val：

class AppUserJdbcRepository(private val jdbcTemplate: JdbcTemplate){

为了完整性：您不应该（忽略罕见的情况）使用“！！”在kotlin中使用运算符，因为这基本上是回到Java的可空性方法。至少根据我的经验，用“？：throw MyCustomException（“jdbcTemplate在初始化过程中为null”）”重新放置它更易于调试，我经常发现考虑它也会暴露出不必要的可空性