可以做录音兼职的网站,个人网站可以做音乐吗,焦作河南网站建设,网站流量30gjax-rs jax-ws有时#xff0c;有必要通过JPA检索大型数据集#xff08;例如#xff0c;超过1,000,000条记录#xff09;#xff0c;并将它们填充到java.util.List的单个实例中是有风险的#xff08;内存障碍#xff09;。 因此#xff0c;这是一个快速的解决方案#… jax-rs jax-ws 有时有必要通过JPA检索大型数据集例如超过1,000,000条记录并将它们填充到java.util.List的单个实例中是有风险的内存障碍。 因此这是一个快速的解决方案它可以解决JAX-RS REST资源端点如何仍能通过“页面”对JPA实体进行流式处理或序列化而在不破坏内存约束的情况下及时提供响应。 示例数据库表和JPA实体 数据库表 为了演示如何实现大数据输出这是我们可以使用的示例MySQL数据库表。 create database large_data_test_db;
use large_data_test_db;create table generated_uuids (record_no bigint not null auto_increment,uuid varchar(100) not null,datetime_generated datetime not null,primary key(record_no),unique(uuid)
);JPA实体 接下来定义代表上述表结构的JPA实体类。 GeneratedUuidEntity.java的代码 package com.developerscrappad;import java.io.Serializable;
import java.util.Date;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;Entity
Table( name generated_uuids )
NamedQueries( {NamedQuery( name GeneratedUuidEntity.listAll, query SELECT u FROM GeneratedUuidEntity u ),NamedQuery( name GeneratedUuidEntity.queryRecordsSize, query SELECT count(u) FROM GeneratedUuidEntity u )
} )
public class GeneratedUuidEntity implements Serializable {private static final long serialVersionUID 12312312234234123L;IdGeneratedValue( strategy GenerationType.IDENTITY )Column( name record_no )private Long recordNo;Column( name uuid )private String uuid;Column( name datetime_generated )Temporal( TemporalType.TIMESTAMP )private Date datetimeGenerated;public GeneratedUuidEntity() {}public GeneratedUuidEntity( Long recordNo ) {this.recordNo recordNo;}public GeneratedUuidEntity( Long recordNo, String uuid, Date datetimeGenerated ) {this.recordNo recordNo;this.uuid uuid;this.datetimeGenerated datetimeGenerated;}public Long getRecordNo() {return recordNo;}public void setRecordNo( Long recordNo ) {this.recordNo recordNo;}public String getUuid() {return uuid;}public void setUuid( String uuid ) {this.uuid uuid;}public Date getDatetimeGenerated() {return datetimeGenerated;}public void setDatetimeGenerated( Date datetimeGenerated ) {this.datetimeGenerated datetimeGenerated;}Overridepublic int hashCode() {int hash 0;hash ( recordNo ! null ? recordNo.hashCode() : 0 );return hash;}Overridepublic boolean equals( Object object ) {// TODO: Warning - this method wont work in the case the id fields are not setif ( !( object instanceof GeneratedUuidEntity ) ) {return false;}GeneratedUuidEntity other ( GeneratedUuidEntity ) object;if ( ( this.recordNo null other.recordNo ! null ) || ( this.recordNo ! null !this.recordNo.equals( other.recordNo ) ) ) {return false;}return true;}Overridepublic String toString() {return com.developerscrappad.GeneratedUuidEntity[ recordNo recordNo ];}
} 在GeneratedUuidEntity中定义了两个命名查询。 GeneratedUuidEntity.queryRecordsSize用于查询表的总记录数而GeneratedUuidEntity.listAll用于检索表中的所有记录。 实施JAX-RS REST资源Java EE方式 让我们有一个名称为JPAStreamingRESTResource的JAX-RS REST资源类其中有一个可用的JPA EntityManager持久性名称 JPAStreamingPU 要注入并通过受保护的方法getEntityManager获得 。 Path( generated-uuids )
Stateless( name JPAStreamingRESTResource, mappedName ejb/JPAStreamingRESTResource )
public class JPAStreamingRESTResource {PersistenceContext( unitName JPAStreamingPU )private EntityManager entityManager;protected EntityManager getEntityManager() {return entityManager;}/*** Say NO to response caching*/protected Response.ResponseBuilder getNoCacheResponseBuilder( Response.Status status ) {CacheControl cc new CacheControl();cc.setNoCache( true );cc.setMaxAge( -1 );cc.setMustRevalidate( true );return Response.status( status ).cacheControl( cc );}
} 此外我们有一个名为getNoCacheResponseBuilder的方法该方法将获得一个非缓存的javax.ws.rs.core.Response.ResponseBuilder 这样以后就不会再得到奇怪的缓存结果了。 JPA调用方法 接下来让我们在资源类中定义两个方法即 queryGeneratedUuidRecordsSize –检索表中的记录总数 private int queryGeneratedUuidRecordsSize() {return getEntityManager().createNamedQuery( GeneratedUuidEntity.queryRecordsSize, Long.class ).getSingleResult().intValue();
} listAllGeneratedUuidEntities –从表中检索所有数据但具有某些限制条件例如记录的开始位置recordPosition和每次往返数据库的最大记录数recordsPerRoundTrip。 目的是“分页”结果以使结果列表不会过分膨胀。 我们稍后会看到它的作用。 private ListGeneratedUuidEntity listAllGeneratedUuidEntities( int recordPosition, int recordsPerRoundTrip ) {return getEntityManager().createNamedQuery( GeneratedUuidEntity.listAll ).setFirstResult( recordPosition ).setMaxResults( recordsPerRoundTrip ).getResultList();
}让流开始 现在让我们实现资源端点方法至少从理论上讲该方法可以在不损害大小的情况下检索数据。 此方法将返回JSON响应其数据格式为 {result: [{record_no: 1,uuid: 34d99089-3e36-4f00-ab93-846b61771eb3,datetime_generated: 2015-06-28 21:02:23},…]
}GETPath( list-all )Produces( application/json )TransactionAttribute( TransactionAttributeType.NEVER )public Response streamGeneratedUuids() {// Define the format of timestamp outputSimpleDateFormat df new SimpleDateFormat( yyyy-MM-dd HH:mm:ss );return getNoCacheResponseBuilder( Response.Status.OK ).entity( new StreamingOutput() {// Instruct how StreamingOutputs write method is to stream the dataOverridepublic void write( OutputStream os ) throws IOException, WebApplicationException {int recordsPerRoundTrip 100; // Number of records for every round trip to the databaseint recordPosition 0; // Initial record position indexint recordSize queryGeneratedUuidRecordsSize(); // Total records found for the query// Start streaming the datatry ( PrintWriter writer new PrintWriter( new BufferedWriter( new OutputStreamWriter( os ) ) ) ) {writer.print( {\result\: [ );while ( recordSize 0 ) {// Get the paged data set from the DBListGeneratedUuidEntity generatedUuidEntities listAllGeneratedUuidEntities( recordPosition, recordsPerRoundTrip );for ( GeneratedUuidEntity generatedUuidEntity : generatedUuidEntities ) {if ( recordPosition 0 ) {writer.print( , );}// Stream the data in Json object formatwriter.print( Json.createObjectBuilder().add( record_no, generatedUuidEntity.getRecordNo() ).add( uuid, generatedUuidEntity.getUuid() ).add( datetime_generated, df.format( generatedUuidEntity.getDatetimeGenerated() ) ).build().toString() );// Increase the recordPosition for every record streamedrecordPosition;}// update the recordSize (remaining no. of records)recordSize - recordsPerRoundTrip;}// Done!writer.print( ]} );}}} ).build();} 电源线说明 实际上这很简单。 诀窍是通过重写write方法来定义匿名类StreamingOutput的表达式该方法首先通过queryGeneratedUuidRecordsSize查询总记录大小然后通过listAllGeneratedUuidEntities逐页检索记录。 此方法将多次访问数据库具体取决于定义的recordsPerRoundTrip值。 JPAStreamingRESTResource.java的完整源代码 package com.developerscrappad;import java.io.BufferedWriter;
import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.text.SimpleDateFormat;
import java.util.List;
import javax.ejb.Stateless;
import javax.ejb.TransactionAttribute;
import javax.ejb.TransactionAttributeType;
import javax.json.Json;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.CacheControl;
import javax.ws.rs.core.Response;
import javax.ws.rs.core.StreamingOutput;Path( generated-uuids )
Stateless( name JPAStreamingRESTResource, mappedName ejb/JPAStreamingRESTResource )
public class JPAStreamingRESTResource {PersistenceContext( unitName JPAStreamingPU )private EntityManager entityManager;private ListGeneratedUuidEntity listAllGeneratedUuidEntities( int recordPosition, int recordsPerRoundTrip ) {return getEntityManager().createNamedQuery( GeneratedUuidEntity.listAll ).setFirstResult( recordPosition ).setMaxResults( recordsPerRoundTrip ).getResultList();}private int queryGeneratedUuidRecordsSize() {return getEntityManager().createNamedQuery( GeneratedUuidEntity.queryRecordsSize, Long.class ).getSingleResult().intValue();}protected EntityManager getEntityManager() {return entityManager;}/*** Say NO to response caching*/protected Response.ResponseBuilder getNoCacheResponseBuilder( Response.Status status ) {CacheControl cc new CacheControl();cc.setNoCache( true );cc.setMaxAge( -1 );cc.setMustRevalidate( true );return Response.status( status ).cacheControl( cc );}GETPath( list-all )Produces( application/json )TransactionAttribute( TransactionAttributeType.NEVER )public Response streamGeneratedUuids() {// Define the format of timestamp outputSimpleDateFormat df new SimpleDateFormat( yyyy-MM-dd HH:mm:ss );return getNoCacheResponseBuilder( Response.Status.OK ).entity( new StreamingOutput() {// Instruct how StreamingOutputs write method is to stream the dataOverridepublic void write( OutputStream os ) throws IOException, WebApplicationException {int recordsPerRoundTrip 100; // Number of records for every round trip to the databaseint recordPosition 0; // Initial record position indexint recordSize queryGeneratedUuidRecordsSize(); // Total records found for the query// Start streaming the datatry ( PrintWriter writer new PrintWriter( new BufferedWriter( new OutputStreamWriter( os ) ) ) ) {writer.print( {\result\: [ );while ( recordSize 0 ) {// Get the paged data set from the DBListGeneratedUuidEntity generatedUuidEntities listAllGeneratedUuidEntities( recordPosition, recordsPerRoundTrip );for ( GeneratedUuidEntity generatedUuidEntity : generatedUuidEntities ) {if ( recordPosition 0 ) {writer.print( , );}// Stream the data in Json object formatwriter.print( Json.createObjectBuilder().add( record_no, generatedUuidEntity.getRecordNo() ).add( uuid, generatedUuidEntity.getUuid() ).add( datetime_generated, df.format( generatedUuidEntity.getDatetimeGenerated() ) ).build().toString() );// Increase the recordPosition for every record streamedrecordPosition;}// update the recordSize (remaining no. of records)recordSize - recordsPerRoundTrip;}// Done!writer.print( ]} );}}} ).build();}
}小心 请记住要调整应用程序服务器的响应连接超时值以防止REST或Http Client抛出java.io.IOException过早的EOF异常。 测试它 要测试它是否有效只需在表中加载567条记录即可。 然后让单元测试调用端点URL并使用以下单元测试代码将检索到的JSON数据保存到文件中使用Apache HttpClient JPAStreamingUnitTest.java的代码 package com.developerscrappad;import java.io.File;
import java.io.FileInputStream;
import static org.junit.Assert.*;import java.nio.file.FileSystems;
import java.nio.file.Files;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.UUID;
import javax.json.Json;
import javax.json.JsonArray;
import javax.json.JsonObject;
import javax.json.JsonReader;
import org.apache.http.HttpEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;public class JPAStreamingUnitTest {private static final String dbDriverClassname com.mysql.jdbc.Driver;private static final String dbUrl jdbc:mysql://localhost:3306/large_data_test_db;private static final String username username;private static final String password password;private static final int numberOfRecords 567;private static final String jsonResultOutputFilename testing123.json;BeforeClasspublic static void setUpClass() {try {Class.forName( dbDriverClassname );try ( Connection conn DriverManager.getConnection( dbUrl, username, password ) ) {String insertSQL insert into generated_uuids (uuid, datetime_generated) values (?, now());try ( PreparedStatement stmt conn.prepareStatement( insertSQL ) ) {for ( int i 0; i numberOfRecords; i ) {System.out.println( Inserting row: i );stmt.setString( 1, UUID.randomUUID().toString() );stmt.executeUpdate();}}}} catch ( final Exception ex ) {ex.printStackTrace();fail( ex.getMessage() );}}AfterClasspublic static void tearDownClass() {try {Class.forName( dbDriverClassname );try ( Connection conn DriverManager.getConnection( dbUrl, username, password ) ) {String truncateSQL truncate generated_uuids;conn.createStatement().executeUpdate( truncateSQL );}new File( System.getProperty( java.io.tmpdir ), jsonResultOutputFilename ).delete();} catch ( final Exception ex ) {ex.printStackTrace();fail( ex.getMessage() );}}Testpublic void testJPAStreaming() {String url http://localhost:8080/JPAStreaming/rest-api/generated-uuids/list-all/;try {CloseableHttpClient httpclient HttpClients.createDefault();HttpGet httpGet new HttpGet( url );try ( CloseableHttpResponse response1 httpclient.execute( httpGet ) ) {System.out.println( response1.getStatusLine() );HttpEntity entity1 response1.getEntity();Files.copy( entity1.getContent(), FileSystems.getDefault().getPath( System.getProperty( java.io.tmpdir ), jsonResultOutputFilename ) );}// Validatetry ( JsonReader jsonReader Json.createReader( new FileInputStream( new File( System.getProperty( java.io.tmpdir ), jsonResultOutputFilename ) ) ) ) {JsonObject jsonObj jsonReader.readObject();assertTrue( jsonObj.containsKey( result ) );JsonArray jsonArray jsonObj.getJsonArray( result );assertEquals( numberOfRecords, jsonArray.size() );SimpleDateFormat validationDF new SimpleDateFormat( yyyy-MM-dd HH:mm:ss );for ( int i 0; i jsonArray.size(); i ) {JsonObject generatedUuidJsonObj jsonArray.getJsonObject( i );int recordNumber generatedUuidJsonObj.getInt( record_no );assertTrue( recordNumber 0 );try {UUID.fromString( generatedUuidJsonObj.getString( uuid ) );} catch ( IllegalArgumentException ex ) {fail( Invalid UUID format at record number: recordNumber );}try {validationDF.parse( generatedUuidJsonObj.getString( datetime_generated ) );} catch ( final NullPointerException | ParseException ex ) {fail( datetime_generated field must not be null and must be of format yyyy-MM-dd HH:mm:ss );}}}} catch ( final Exception ex ) {ex.printStackTrace();fail( ex.getMessage() );}}
} 我们完成了。 感谢您的阅读希望对您有所帮助。 翻译自: https://www.javacodegeeks.com/2015/07/how-to-streamserialize-jpa-result-as-jax-rs-response-for-large-data.htmljax-rs jax-ws
