Spring JdbcTemplate 是JDBC核心包中的中心类。它简化了 JDBC 与 Spring 的使用，并有助于避免常见错误。在此页面上，我们将学习使用它的queryForObject 方法。
JdbcTemplate.queryForObject不同参数的方法。
1.
<T> T queryForObject(String sql, Class<T> requiredType) throws DataAccessException 执行给定的 SQL 并返回所需类型的对象。
2.
<T> T queryForObject(String sql, Class<T> requiredType, @Nullable Object... args) throws DataAccessException 查询给定的 SQL 以从 SQL 创建预准备语句和要绑定到查询的参数列表，需要一个结果对象。
3.
<T> T queryForObject(String sql, Object[] args, int[] argTypes, Class<T> requiredType) throws DataAccessException 查询给定的 SQL 以从 SQL 创建预准备语句和要绑定到查询的参数列表，需要一个结果对象。
4.
<T> T queryForObject(String sql, Object[] args, int[] argTypes, RowMapper<T> rowMapper) throws DataAccessException 查询给定的 SQL，用于从 SQL 创建预准备语句和要绑定到查询的参数列表，通过 RowMapper将单个结果行映射到结果对象。
5.
<T> T queryForObject(String sql, RowMapper<T> rowMapper) throws DataAccessException 执行给定静态 SQL 的查询，通过RowMapper将单个结果行映射到结果对象。
6.
<T> T queryForObject(String sql, RowMapper<T> rowMapper, @Nullable Object... args) throws DataAccessException 查询给定 SQL 以从 SQL 创建预准备语句和要绑定到查询的参数列表，通过RowMapper将单个结果行映射到结果对象。
参数：
sql是要执行的 SQL 查询。
requiredType 是结果对象应匹配的类型。
args 是要绑定到查询的参数。
argType是参数的 SQL 类型java.sql.Types。
rowMapper是一个回调，它将每行映射一个对象
返回：
结果对象，如果是 SQL NULL，则为 null。
抛出：
如果执行查询时遇到任何问题，则抛出DataAccessException。
使用Spring Boot的示例
PersonDAO.java
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package com.concretepage;
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import java.sql.ResultSet;
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import java.sql.SQLException;
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import org.springframework.beans.factory.annotation.Autowired;
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import org.springframework.jdbc.core.JdbcTemplate;
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import org.springframework.jdbc.core.RowMapper;
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import org.springframework.stereotype.Repository;
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@Repository
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public class PersonDAO {
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@Autowired
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private JdbcTemplate jdbcTemplate;
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// queryForObject(String sql, Class<T> requiredType)
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public int getPersonCount() {
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String sql = "select count(*) from person";
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return jdbcTemplate.queryForObject(sql, Integer.class);
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}
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// queryForObject(String sql, Class<T> requiredType, Object... args)
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public String getNameById(int id) {
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String sql = "select name from person where id = ?";
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return jdbcTemplate.queryForObject(sql, String.class, 1);
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}
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// queryForObject(String sql, Object[] args, int[] argTypes, Class<T> requiredType)
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public int getPersonCountByNameAndAge(String name, int age) {
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String sql = "select count(*) from person where name = ? and age = ?";
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Object[] args = {name, age};
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int[] argTypes = {java.sql.Types.CHAR, java.sql.Types.INTEGER};
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return jdbcTemplate.queryForObject(sql, args, argTypes, Integer.class);
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}
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// queryForObject(String sql, Object[] args, int[] argTypes, RowMapper<T> rowMapper)
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public Person getPersonsById(int id) {
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String sql = "select * from person where id = ?";
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Object[] args = {id};
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int[] argTypes = {java.sql.Types.INTEGER};
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return jdbcTemplate.queryForObject(sql, args, argTypes, new RowMapper<Person>() {
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@Override
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public Person mapRow(ResultSet rs, int rowNum) throws SQLException {
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Person p = new Person(rs.getString(2), rs.getInt(3));
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p.setId(rs.getInt(1));
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return p;
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}
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});
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}
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// queryForObject(String sql, RowMapper<T> rowMapper)
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public Person getAdmin() {
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String sql = "select * from person where id = 1";
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return jdbcTemplate.queryForObject(sql, new RowMapper<Person>() {
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@Override
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public Person mapRow(ResultSet rs, int rowNum) throws SQLException {
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Person p = new Person(rs.getString(2), rs.getInt(3));
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p.setId(rs.getInt(1));
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return p;
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}
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});
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}
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// queryForObject(String sql, RowMapper<T> rowMapper, Object... args)
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public int getPersonCount2(String name, int age) {
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String sql = "select count(*) from person where name = ? and age = ?";
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return jdbcTemplate.queryForObject(sql, new RowMapper<Integer>() {
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@Override
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public Integer mapRow(ResultSet rs, int rowNum) throws SQLException {
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return rs.getInt(1);
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}
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}, name, age);
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}
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}
Person.java
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package com.concretepage;
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public class Person {
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private int id;
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private String name;
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private int age;
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public Person(String name, int age) {
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this.name = name;
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this.age = age;
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}
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public int getId() {
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return id;
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}
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public void setId(int id) {
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this.id = id;
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}
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public String getName() {
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return name;
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}
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public int getAge() {
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return age;
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}
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}
application.properties
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spring.datasource.url=jdbc:mysql://localhost:3306/concretepage?autoReconnect=true&useSSL=false&useUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai
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spring.datasource.username=root
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spring.datasource.password=root
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spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
pom.xml
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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>com.concretepage</groupId>
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<artifactId>soap-ws</artifactId>
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<version>0.0.1-SNAPSHOT</version>
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<packaging>jar</packaging>
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<name>spring-demo</name>
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<description>Spring Demo Application</description>
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<parent>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-parent</artifactId>
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<version>2.7.4</version>
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<relativePath />
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</parent>
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<properties>
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<java.version>16</java.version>
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</properties>
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<dependencies>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter</artifactId>
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</dependency>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-jdbc</artifactId>
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</dependency>
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<dependency>
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<groupId>mysql</groupId>
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<artifactId>mysql-connector-java</artifactId>
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<version>8.0.30</version>
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</dependency>
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</dependencies>
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<build>
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<plugins>
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<plugin>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-maven-plugin</artifactId>
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</plugin>
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</plugins>
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</build>
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</project>
MyApplication.java
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package com.concretepage;
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import org.springframework.boot.SpringApplication;
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import org.springframework.boot.autoconfigure.SpringBootApplication;
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import org.springframework.context.ApplicationContext;
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@SpringBootApplication
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public class MyApplication {
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public static void main(String[] args) {
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ApplicationContext ctx = SpringApplication.run(MyApplication.class, args);
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PersonDAO personDAO = ctx.getBean(PersonDAO.class);
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System.out.println("Total Count: " + personDAO.getPersonCount());
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System.out.println(personDAO.getNameById(1));
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System.out.println("Count: " + personDAO.getPersonCountByNameAndAge("Mohan", 25));
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Person p = personDAO.getPersonsById(1);
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System.out.println(p.getId() + " - " + p.getName() + " - " + p.getAge());
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Person admin = personDAO.getAdmin();
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System.out.println(admin.getId() + " - " + admin.getName() + " - " + admin.getAge());
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System.out.println("Count: " + personDAO.getPersonCount2("Mohan", 25));
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}
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}
查找我们的演示中使用的 MySQL 表（人）屏幕截图。
输出。
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Total Count: 3
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Rakesh
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Count: 2
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1 - Rakesh - 30
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1 - Rakesh - 30
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Count: 2
参考
下载源代码
转载：https://blog.csdn.net/allway2/article/details/127604005
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