java - 如何解决 HibernateTemplate 的 find(String query) 方法抛出的 NullPointerException

Question

如何解决这个 NullPointerException ？一点背景知识，我正在开发一个基于 Spring 的项目，并在 DAO 层使用 HibernateTemlate 来完成所有数据库相关操作。

这是我从抛出 NullPointerException 的测试类中提取的代码片段。

   try {
                   List<Object[]> list = (List<Object[]>) ht.find("select uomId,uomModel from in.nit.model.Uom");
                   System.out.println(list);
               }catch(NullPointerException e) {
                   e.printStackTrace();
               }

这是控制台上异常的堆栈跟踪。

```
java.lang.NullPointerException
    at in.nit.dao.impl.UomDaoImplTest.test(UomDaoImplTest.java:28)
    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:567)
    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)
```

Here is my model class

```
@Entity
@Table(name="uomtab")
public class Uom {

    @Id @GeneratedValue @Column(name="umid") private Integer uomId;
    @Column(name="utype") private String uomType;
    @Column(name="umodel") private String uomModel;
    @Column(name="udesc") private String uomDesc;

    public Uom() {
        super();
    }

    public Uom(Integer uomId) {
        this.uomId = uomId;
    }

    public Integer getUomId() {
        return uomId;
    }
    public void setUomId(Integer uomId) {
        this.uomId = uomId;
    }
    public String getUomType() {
        return uomType;
    }
    public void setUomType(String uomType) {
        this.uomType = uomType;
    }
    public String getUomModel() {
        return uomModel;
    }
    public void setUomModel(String uomModel) {
        this.uomModel = uomModel;
    }
    public String getUomDesc() {
        return uomDesc;
    }
    public void setUomDesc(String uomDesc) {
        this.uomDesc = uomDesc;
    }
    @Override
    public String toString() {
        return "Uom [uomId=" + uomId + ", uomType=" + uomType + ", uomModel=" + uomModel + ", 
      uomDesc=" + uomDesc + "]";
    }
}

```

此外，尽管 find(String Query) 方法已被弃用，但我在项目的其他 dao 类中广泛使用了它，它工作顺利且良好。

此异常导致我的代码崩溃的可能原因是什么？

Answer 1

1. 你不应该捕获 NullPointerException
2. 代码中的第 28 行是什么？
3. 您尝试过调试线路吗？如果是 ht.find 行，唯一有意义的是您的 HibernateTemplate 为 null 并且尚未正确设置。