如何解决从HibernateTemplate的find(String query)方法中抛出的这个NullPointerException。

Question

如何解决此NullPointerException？有一点背景知识，我正在开发一个基于Spring的项目，并在DAO层使用Hibernate Temlate来完成所有与数据库相关的操作。

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。

```
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(StringQuery(方法被弃用，但我已经在项目的其他dao类中广泛使用了它，它运行得很顺利。

这个异常导致我的代码崩溃的可能原因是什么？

Answer 1

1. 您不应该捕获NullPointerException
2. 代码中的第28行是什么
3. 你试过调试线路了吗？如果是ht.find行，那么唯一有意义的是你的Hibernate模板为null并且没有正确设置

Answer 2

您的错误在类"UomDaoImplTest"中。这与Hibernate模板无关。你能公布你的测试课吗。